Art. 430, Part VII provides the requirements for motor controllers. The requirements for motor control circuits are in Part VI. What’s the difference? Part VI is about the supply power to motor controllers. The intention of Part VII is to require suitable controllers for all motors [430.81]. Controllers for smaller motors have special requirements:
A controller must be capable of:
Additional requirements apply to autotransformers [430.82(B)] and rheostats [430.82(C)]. A controller doesn’t need to open all conductors to a motor [430.84] unless it also serves as a disconnecting means [Exception]. The requirements for controller ratings are a bit confusing. Begin with the general rule: The horsepower rating of the controller can’t be lower than the horsepower rating of the motor [430.83(A)(1)]. Then look through the special cases to see if you are working with one of those:
Each motor must be provided with its own controller [430.87], but there are four exceptions. Adjustable speed motors can’t be started under a weakened field unless the motor in question is designed for such starting [430.88]. Speed limiting is required for three types of motors or machines, for example series motors, and there are two exceptions [430.89]. If you use a combination fuseholder and switch as a controller, the fuseholder must accommodate the size of fuse specified in Art. 430, Part III for motor overload protection.
I. General This article covers requirements for motors, motor branch circuit and feeder conductors and their protection, motor overload protection, motor control circuits, motor controllers, and motor control centers. There are general and specific requirements. Figure 430.1 in the NEC® describes where in Article 430 different parts of the circuits are covered as well as other articles. This article does not cover air-conditioning and refrigeration equipment, which is covered in Article 440 and motor control centers which is covered in 110.26(F).
There are numerous other articles with which motor and controllers must comply for special cases. These are noted in Table 430.5.
Generally, the conductor size is determined by using the allowable ampacity tables as noted in Section 310.15(B) or calculated as noted in Section 310.15(C). Use Section 400.5 to determine flexible cord conductor size. (A) General Motor Applications. Tables 430.147 through 430.150 are used to determine ampere rating for sizes of wire, switches, circuit protection, and the like (not the nameplate ratings). If the motor has a marking in amperes but not horsepower, it is assumed that the horsepower ratings correspond to those in Tables 430.247 through 250. Motors with speeds less than 1200RPM and high-torque motors can have higher full load currents. Multispeed motors have full load currents that vary with speed. In these cases, use the nameplate current ratings. There are three exceptions. Separate motor overload protection is based on the nameplate reading. (B) Torque Motors. The rated current to be used for these motors is the locked-rotor current. This nameplate value is used to determine the size of the branch circuit conductors as noted in Sections 430.22 and 430.24, the rating of the overload protection, and the rating of the motor overload protection and the rating of the branch circuit short circuit and ground fault protection. (C) Alternating Current Adjustable Voltage Motors. For these types of motors use the maximum operating current marked on the motor. If there is no marking, then use 150% of the values in Tables 430.149 and 430.150.
Table 430.10(B) indicates the minimum wire bending space at the terminals of enclosed motors.
Tables 430.10(B), 430.12(B), 430.12(C)(1), and 430.12(C)(2) give various dimension and space requirements. There is also information on connections.
If this is to be determined for compliance with Sections 430.24, 430.53(B), and 430.53(C), use the rated full-load current from Tables 430.147, 430.148, 430.149, and 430.150.
II. Motor Circuit Conductors The rules of this part apply to circuits supplying motors at 600 V or less. Generally size conductors at 125% of the motor full-load rated current as noted in Section 430.6(A)(1) for the supply to a single motor rated for continuous duty. There is an exception to this rule. It is for direct-current motors that operate from a single-phase power supply which is rectified. There are regulations for multispeed motors and wye-start delta-run motors and part winding motors. When the junction box is allowed to be separated from the motor, a special exception is made for wire size on motors of 1 hp or less. There are provisions for other than continuous-duty motors.
The secondary leads for a continuous-duty wound-rotor motor must be rated at least 125% of the full-load secondary current. If the motor is not continuous, Table 430.22(E) must be used. Table 430.23(C) is used when the secondary resistor is separate from the controller.
In this case the conductors are rated at 125% of the full load current of the largest motor (the same as a single motor) plus the full-load current of all additional motors plus the ampere rating of the other loads which are calculated in accordance with Article 430.6(A) and other sections of the NEC®. There are three exceptions: continuous-duty, motor-operated fixed space heating, and interlocked motors.
The conductors for these loads are based, as a minimum, on the circuit ampacity marked on the equipment in accordance with Section 430.7(D). If the equipment is not factory wired, and the nameplates visible as per Section 430.7(D)(2), the conductors are calculated in accordance with Section 430.24.
If all motors will not operate simultaneously for any number of reasons, the authority having jurisdiction can allow the use of a demand factor.
Feeder tap conductors must be sized at least according to Part II of this section and either be enclosed and 3.0 m (10 ft.) or less in length or be one-third or more of the rating of the feeder, 7.5 m (25 ft.) or less in length, and protected or have an ampacity not less than the feeder conductors. There is an exception for feeder taps over 7.5 m (25 ft.) in high bay manufacturing buildings. There are additional rules.
III. Motor and Branch-Circuit Overload Protection The overload protection is usually the thermal overloads in the controller or starter. It should not be confused with the short-circuit protection, which is the fuse or circuit breaker in the panelboard. Diagram 430.1 in the Code should be referred to, as well as Annex D, Example No. D8.
There are four methods acceptable: (A) More than 1 Horsepower
(B) One Horsepower or Less, Automatically Started. Here again there are four acceptable methods; the first three are similar to the first three for motors rated more than 1 hp. These include separate devices (ratings are indicated), thermal protectors, and cases where no additional protection other than branch-circuit protection is required (where protection is integral with the motor). A fourth case is that where the impedance of the motor protects against overheating when the motor does not start. (C) Selection of Overload Relay. In the event the ratings chosen as listed in Section 430.32(a)(1) and (c)(1) will not allow the motor to start, this section gives larger permissible ratings. (D) One Horsepower or Less, Nonautomatically Started. If not permanently installed then if it is within sight of the controller location, the ground-fault protection and branch-circuit short-circuit protection is sufficient. The sizings noted in Part IV are to be used. It can be on a 120-V circuit rated 20 A or less. If not within sight of the controller or permanently installed, it must comply with Section 430.32(B). If permanently installed comply with 430.32(B). (E) Wound Rotor Secondaries. These can be protected by the motor-overload device.
You can omit the separate overload protection for these types of motors and use only the branch-circuit, short-circuit and ground- fault protective device.
There are cases where the overload protection can be shunted during starting.
When used as overload protection, put one in each ungrounded conductor and also the grounded conductor if the supply is three-phase, three-wire ac with one phase grounded.
Table 430.37 gives the requirements.
The number of conductors to be opened must prevent current to the motor for devices other than fuses or thermal protection.
This is permitted if it is in accordance with Table 430.37 and operator in the running position and also in the starting position for an ac motor. If the device used for motor overload protection cannot clear short circuits, they must be protected by either fuses or circuit breakers or a motor short-circuit protector sized as noted in Section 430.52. There is one exception to the sizing rulegroup installations and where an overload relay is used.
This section indicates what overload protection must be used when motors are connected to general-purpose branch circuits. It must also comply with Article 210. (A) Not over 1 Horsepower. Can be connected without overload protection if the rules of Section 430.32(B) and (D) and Section 430.53(A)(1) and (A)(2) are followed. (B) Over 1 Horsepower. Each motor must have overload protection as noted in Section 430.32. (C) Cord- and Plug-Connected. If no overload protection is provided, as in (a) above, the ratings of the plug and receptacle cannot be larger than 15 A 125 V or 10 A 250 V. If protection is required as in (b) above, the overload device must be part of the motor or appliance. (D) Time Delay. Time delay must be provided in the branch-circuit and ground-fault devices to let the motor start.
If an orderly shutdown is necessary to protect people rather than a quick opening of the circuit, the overload device can be connected to an alarm rather than open the circuit under the provisions of this section. IV. Motor Branch-Circuit, Short-Circuit, and Ground-Fault Protection
The device must carry the starting current. Table 430.152 lists the maximum settings of the protective devices. If the values in the tables are not a standard-size device, the rating can be increased to the next highest rating. If the rating in the table will not permit the motor to start, the rating can be increased as follows:
Also listed in this section are the rules for when instantaneous trip circuit breakers and motor short-circuit protectors can be used; rules for multispeed motors; multispeed motor; power electronic devices; rules for torque motors; and rules for phase converters. Where a maximum rating is indicated by the manufacturer, it cannot be exceeded. The reader is referred to this section of the Code for complete information.
This section indicates under what conditions two or more motors or combined loads are permitted on one branch circuit. (A) If none of the motors is greater than 1 hp, the circuit is protected at 20 A at 120 V or not more than 15 A at 600 V, the full-load current of each motor is not more than 6 A, individual overload protection meets the requirements of Section 430.32, and the rating marked on any controller for branch-circuit short circuit and ground-fault protection is not exceeded, more than one motor or combination loads are permitted on one branch circuit. (B) When the branch-circuit short-circuit and ground-fault protective devices rating is not larger than required for the smallest motor and all motors have individual overload protection and the combination load will operate under these conditions, more than one motor or combination loads are permitted. (C) Group installations of more than one motor or combination loads are permitted on one branch circuit if the overload devices and motor controllers are in a listed factory assembly, and motor short circuit and ground-fault protection are in the assembly or noted on the assembly; or if the controllers, overload devices, branch circuit, short circuit, and ground-fault devices are field-installed separately with manufacturer's instructions for use with each other and the following conditions are met:
(D) In a group installation as described in (c) above, if the conductors to any single motor are not larger than the branch-circuit conductors or are not less than one-third the rating of the branch-circuit conductors in accordance with Section 430.22, and not farther than 7.5 m (25 ft.) from the controller and physically protected, then installation will not require individual branch-circuit short-circuit and ground-fault protection.
The branch-circuit short-circuit and ground-fault device rating must not be larger than the rating marked on the equipment and comply with Section 430.7(D).
As long as the rating is not larger than that required for overload protection in Section 430.32, the branch-circuit short-circuit and ground-fault protection and overload protection can be in one device.
V. Motor Feeder Short-Circuit and Ground-Fault Protection
The rating must be that of the largest branch-circuit protective device plus the full-load currents of all other motors. If larger feeders have been installed for future expansion, the rating can be that of the feeder. Reference is made to Sections 430.52 and 440.22(A). There are two exceptions and additional requirements.
When combined loads are installed in one feeder, the rating can be sufficient to carry the lighting and appliance load plus that permitted by Section 430.52 for a single motor and Section 430.62 for more than one motor and 440.22 for a single hermetic refrigerant motor-compressor. There is an excpetion for a motor control center. VI. Motor Control Circuits This part applies to particular conditions and contains modifications of general requirements of motor control circuits.
If the circuit is tapped from the load side of a branch-circuit protective device, it must have protection as specified in Section 430.72. If not, it must be protected as specified in Section 725.23. There are two exceptions to this rule. There are also requirements for a control circuit transformer and additional requirements for conductor protection.
Motor control circuits must have a disconnecting means. One device can disconnect both the motor and control circuits from power, or separate ones can be used. If a transformer is used to reduce the voltage for the control circuit and it is located in the controller enclosure, the disconnecting means must be in the supply side of the transformer. There are a number of exceptions. VII. Motor Controllers The intention of this part is to require suitable controllers for all motors. When the motor is stationary and of not more than 1/8 hp, the branch-circuit protective device can be used if the motor is normally left running and cannot be damaged by not starting or by overloads. The plug and receptacle can be the controller if the motor is portable and not more than 1/3 hp.
Generally, it must have a horsepower rating at least equal to that of the motor. There are a number of additional rules.
Unless it serves as a disconnecting device, it does not have to open all conductors.
This is permitted if it also simultaneously opens all other conductors.
Each motor must normally have its own controller. There are exceptions to this rule if the motors are rated at not more than 600 V and the single controller is rated at not less than the sum of all motors it will control. Under these conditions it is allowed if more than one motor is used in one device or one overcurrent device is used for a group of motors [Section 430.53(A)] or the motors are in one room in sight of the controller.
VIII. Motor Control Centers A motor control center is an assembly of enclosed sections which principally contain motor control units and have a common power bus.
They must have overcurrent protection, either an overcurrent device upstream or a main device in the motor control center. It must be in accordance with Parts A, B and I of Article 240 and sized in accordance with the common power bus.
All sections must be bonded with an equipment grounding conductor or grounding bus in accordance with Table 250.95. All equipment grounding conductors must terminate here. In the case of a single section a grounding termination point must be provided.
(A) Support and Arrangement. They must be protected from damage and held firmly. Only the conductors connected or used for control are allowed in a section. (B) Phase Arrangement. Three phase buses are arranged A, B, C, left to right, top to bottom, or front to back when standing in the front. (C) Minimum Wire Bending Space. As noted in Article 373. (D) Spacings. As noted in Table 430.97. (E) Barriers. Used in service-entrance motor control centers. IX. Disconnecting Means
It must be provided for and in sight from the controller location. An exception is made for motors over 600 V if it can be locked out and a warning sign is posted. Also, one disconnect can be used for a group of controllers for a multimotor device. A disconnecting means must also be located within sight of the motor location except in accordance with Section 430.102(a). There are some additional exceptions.
If all conductors are opened simultaneously, one pole can be in a grounded conductor.
The disconnecting device must be noted in (A) below unless permitted in (B) through (G) meeting the specified conditions. (A) General. It must be a horsepower-rated motor circuit switch. It can also be a molded case circuit breaker, molded case switch, an instantaneous trip circuit breaker which is part of a combination motor controller, a self-protected combination controller, or a manual motor controller if it is marked as such, if it is installed between the motor and the final motor branch circuit and ground-fault protective device, all of the items being listed. There are additional requirements for a manual motor controller. System isolation equipment must be listed for disconnection purposes and must be installed on the load side of the overcurrent protection and its disconnecting means. The disconnecting means must be one of those noted in 430.109(A)(1) through (A)(3). (B) Stationary Motors of 1/8 Horsepower or Less. The branch circuit overcurrent device can be used. (C) Stationary Motors of 2 Horsepower or Less. Stationary motors 2 hp or less and 300 V or less can have a general-use switch rated twice that of the motor. On ac circuits a general-use snap switch listed for ac use only can be used if the motor is not more than 80% of the rating of the switch. A listed manual motor controller can also be used if it is marked as being suitable as a motor disconnect and it is horsepower rated not less than the rating of the motor. (D) Autotransformer-Type Controlled Motors. Motors over 2 hp up to 100 hp can use a general-use switch for motors with autotransformer controllers if the motor drives a generator with overload protection; the controller can interrupt locked rotor current, has no voltage release, and has running overload protection not larger than 125% of full-load current; separate fused or inverse time circuit breakers are provided and rated not more than 150% of full load current. (E) Isolating Switches. Stationary motors more than 40 hp dc or 100 hp ac can have a general use or isolating switch if marked "Do Not Operate Under Load." (F) Cord- and Plug-Connected Motors. A horsepower rated attachment plug and receptacle rated at least the rating of the motor can be used. This is not required for cord and plug appliances (Section 422.32), room air conditioners (Section 440.63) or a portable motor 1/3 hp or less. (G) Torque Motors. A general-use switch can be used for a torque motor.
(A) The disconnecting means must have a rating of at least 115% of the full-load current rating of the motor. There is an exception. (B) It must have a rating of at least 115% of the nameplate current for torque motors. (C) For combination loads of motors or motors and other types of loads, the ratings of the disconnect must not be less than 115% of the total of the full-load current of all the loads. The Code makes reference to the method of determining the combined load.
A switch or circuit breaker can be used as the disconnect and controller if it complies with Section 430.83: if it opens all ungrounded conductors to the motor, has an overcurrent protective device which opens all ungrounded conductors to the switch, and is either an air-break switch, an inverse time circuit breaker, or an oil switch.
Generally, a motor must have its own disconnecting means. There is an exception.
Generally, each source must have a disconnect. There are two exceptions. X. Adjustable-Speed Drive Systems
XI. Over 600 Volts, Nominal
XII. Protection of Live PartsAll Voltages
If operating at 50 V or more, the exposed live parts must be guarded against accidental contact by enclosure or location. This can be done in a special room or enclosure, on a balcony or by installation at least 2.5 m (8 ft.) above the floor. There is an exception.
If the only guards are by location, as noted in Section 430.132, then insulating mats or platforms are required. XIII. GroundingAll Voltages
The frames must be grounded if in a wet location and not isolated, supplied by wire in a metal enclosure, in a hazardous location, or if motor operates over 150 V to ground.
XIV. Tables Page 2
I. General This section states the scope.
Many additional articles are listed, such as 422, 424, 430, 460, and 470, and some not in Chapter 4.
The rating on the nameplate is to be used for a hermetic refrigerant motor compressor. There are two exceptions. Conductors are to be chosen from Tables 310.16 through 310.19 or in accordance with Section 310.15. Requirements are noted for multimotor equipment.
A refrigerating system or air-conditioning system can be considered in accordance with Section 430.87, Exception, and Section 430.112, Exception. II. Disconnecting Means
For hermetic refrigerant motor-compressor it must be at least 115% of the larger of the rated load or branch-circuit election circuit. There is an exception. If the rated load or locked rotor current comes out to be 100 hp or larger, use the provisions of Section 430.109(E). Information is given concerning equivalent horsepower and locked rotor current. Additional information is given concerning combination loads, horsepower rating, full load equivalent, small motor compressors and disconnecting means.
The separable connector or plug and receptacle can be used as the disconnecting means. It must be within sight and readily accessible to the equipment. There are two exceptions. III. Branch-Circuit Short-Circuit and Ground-Fault Protection
(A) Rating or Setting for Individual Motor-Compressor. It must allow the motor to start. The NEC® therefore permits a rating or setting of up to 175% of the larger of the motor load or branch-circuit selection current. This can be increased to 225% if necessary. A 15-A rating is the least that can be required for branch-circuit, short-circuit and ground-fault protection. (B) Rating or Setting for Equipment. It must also allow the equipment to start. If only one hermetic refrigerant motor compressor is used, conform to Section 422(A). If more than one hermetic refrigerant motor compressor is used, conform to Section 430.53 and the following:
(C) If a maximum rating is indicated by the manufacturer, it should not be exceeded. IV. Branch-Circuit Conductors
The rating cannot be less than 125% of the largest of the motor compressor rated load or branch-circuit selection current. There is additional information concerning wye-start, delta-run motor compressor.
The ampacity must be the sum of the larger of the rated load or branch-circuit selection currents of all the motor-compressor loads plus full-load currents of the other motors plus 25% of the largest motor. There are two exceptions to this: one is for room air conditioners as per Part VII and the other is for interlocked motors. The capacity must be adequate for all other loads, plus the motor-compressor load as specified in Sections 430.32 and 440.33. An exception is also made for interlocked circuitry.
It cannot be less than that marked on the equipment as per Section 440.4(B). V. Controller for Motor-Compressors Generally, use the nameplate ratings. If more than one load is served, use the combined load rating [refer to Section 440.12(B)]. There are additional requirements. VI. Motor Compressor and Branch-Circuit Overload Protection
(A) Protection of Motor-Compressor. The following methods can be used: (1) an overload relay that will trip at not more than 140% of motor full-load current; (2) a thermal protector integral with the motor compressor; (3) a fuse or inverse time circuit breaker responsive to motor current and rated not more than 125% of motor current; and (4) a protective system furnished with the unit or specified for the unit. (B) Protection of Motor-Compressor Control Apparatus and Branch-Circuit Conductors. It can be the same device protecting the motor-compressor in accordance with Section 440.52(A). There is an exception.
VII. Provisions for Room Air Conditioners
The branch circuit can have a load of only 80% of its rating for a cord- and plug-connected air-conditioning unit, if no other loads are on the circuit. If other loads are on the circuit, then the load of the cord- and plug-connected air-conditioning unit cannot be more than 50% of the rating of the branch circuit.
The attachment plug can be used for a single-phase unit at 250 Volts or less if the manual control on the unit is readily accessible and within 1.8 m (6 ft.) of the floor or if a manual disconnecting means is readily accessible within sight of the unit. The length of the cord cannot be larger than 3 m (10 ft.) for 120 V or 1.8 m (6 ft.) for 208 to 240 V.
The following article titles are listed for reference: Article 445Generators; Article 450Transformers and Transformer Vaults (Including Secondary Ties); Article 455Phase Converters; Article 460Capacitors; Article 470Resistors and Reactors; Article 480Storage Batteries; Article 490Equipment, over 600 Volts, Nominal. Page 3
Articles 500 through 504 describe the electrical and electronic equipment and wiring requirements in hazardous (classified) locations where a fire or explosion hazard can exist because of flammable gases or vapors, flammable liquids, combustible dust, or ignitible fibers or flyings. There are fine print notes.
All applicable sections of this Code apply unless they are modified by Articles 500 through 504. (A) Documentation. All areas that are classified must have the proper documentation. This documentation must be available. Note: Space does not permit a complete description of this chapter. This is true of the entire NEC® but is again stated here. Only the highlights are noted. The reader should refer to the NEC® for complete descriptions. (B) Reference Standards
(A) Classifications of Locations. The classifications are made by the properties of the items in the room under the listings in this chapter. (B) Class I Locations. Areas where flammable gases or vapors are in the air in quantities that can cause explosive or ignitible mixtures are classified as Class I. They are further broken down into two divisions: (1) Class I, Division 1. This is where ignitible concentrations of gases or vapors can exist normally; where they may exist because of maintenance or leakage; or where they might exist because of breakdowns or faulty operations. (2) Class I, Division 2. This is where volatile flammable liquids or flammable gases are used but are normally in closed containers or systems and can escape only as a result of a breakdown or rupture; where ignitible concentration of gases or vapors normally cannot occur because of mechanical ventilation; where an area is next to a Class I, Division 1, location and some leakage between areas occurs. (C) Class II Locations. These are hazardous because of combustible dust. They are also broken down into two divisions. (1) Class II, Division 1. This is where combustible dust is in the air and can ignite under normal conditions due to its concentration, or where a breakdown of equipment can cause these concentrations and an ignitible source, or Group E combustible dust may be present in hazardous quantities. (2) Class II, Division 2. This is where combustible dust is in quantities in the air to have explosive or ignitible mixtures due to abnormal operations; or the combustible dust is not in high enough quantities to interfere with the normal operations of electrical equipment or other apparatus but it could be suspended in the air if there were infrequent malfunctions of the equipment; or where the accumulations of the combustible dust in the vicinity of electrical equipment could become ignitible or interfere with the safe dissipation of heat from the electrical equipment as a result of abnormal operation of this equipment. (D) Class III Locations. Areas that have ignitible fibers or flyings in a concentration not likely to cause ignition are classified as Class III. They are also further broken down into two divisions. (1) Class III, Division 1. Areas where the fibers or flyings are handled, manufactured, or used. (2) Class III, Division 2. Areas where the fibers or flyings are stored or handled other than in the process of manufacture. This section indicates the groupings of various air mixtures. Requirements are given for approval for class and properties, marking, and temperature.
This paragraph describes various protection techniques which are acceptable for electrical and electronic equipment in hazardous (classified) locations. This paragraph describes the equipment construction and installation. 500.9 Specific Occupancies These are covered in Articles 510 through 517 and include garages, aircraft hangars, gasoline dispensing and service stations, bulk storage plants, spray application, dipping and coating processes, and health care facilities. Page 4
I. General
This article refers to those areas classified as Class I in Section 500.5. II. Wiring (A) Class I, Division 1. Only threaded rigid metal conduit, threaded steel intermediate conduit, or Type MI cable can be used. Boxes and fittings must be approved for Class I, Division 1. At least five threads must be engaged. MI cable has to be installed to prevent stress at the terminations. There is one exception. There are also requirements for industrial establishments with the use of MC-HC and ITC-HC cable. (B) Class I, Division 2. Methods permitted are threaded rigid metal conduit; threaded steel intermediate metal conduit; enclosed gasketed busways; enclosed gasketed wire-ways; Type MI, MC, MV, or TC cable with approved terminations; Type PLTC cable; type ITC cable as permitted in 727.4 and all methods permitted in 501.10(A). Explosion-proof boxes or fittings are not required. Additional requirements and exceptions are noted.
Seals must be provided and approved items must be used. (A) Conduit Seals, Class I, Division 1
(B) Conduit Seals, Class I, Division 2
(C) Class I, Divisions 1 and 2. These are general rules.
(D) Cable Seals, Class I, Division 1 (E) Cable Seals, Class I, Division 2 (F) Drainage. In certain cases drainage of accumulated liquid is permitted and even required. Special requirements must be followed.
If the conductors come in contact with condensed vapors or liquids, the insulation must be identified for this use or have protection provided by a lead sheath or another approved sheath.
There can be no uninsulated exposed parts such as conductors, buses, etc., that operate at more than 30 volts. This limit is reduced to 15 volts in wet locations. The protection must be in accordance with 500.7(E), 500.7(F), or 500.7(G).
Wiring and equipment must be grounded in accordance with Article 250. Bonding jumpers with proper fitting or other approved means of bonding must be used. Locknut bushings and double locknut types of contacts are not acceptable. The means of bonding applies to all raceways, fittings, boxes, enclosures, etc., between Class I locations and the grounding point for service equipment or separately derived systems. If flexible conduit is used it must have internal or external bonding jumpers in parallel with each conduit. It must also comply with the requirements of Section 250.120 where flexible metal or liquidtight flexible metal conduit is used. There are exceptions.
III. Equipment
(A) Class I, Division 1
(B) Class I, Division 2. In these locations they must be in accordance with Sections 450.21 through 450.27.
(A) Class I, Division 1. They must be in Class I, Division 1 enclosures. (B) Class I, Division 2
(A) Class I, Division 1. Must be in an enclosure and the entire assembly must be identified for Class I locations. (B) Class I, Division 2
Transformers, impedance coils, and resistors are covered by this section. (A) Class I, Division 1. In this location they must have enclosures identified for Class I, Division 1. (B) Class I, Division 2. In this location switching mechanisms must be in accordance with Section 501.6(B). General-purpose enclosures can be used for coils and windings. Resistors must have enclosures identified for Class I locations. If the resistor is fixed and the maximum operating temperature is not more than 80% of the ignition temperature of the gas or vapor, a general-purpose enclosure can be used.
(A) Class I, Division 1. In this location they must be either identified for Class I, Division 1 locations or be totally enclosed with a positive pressure ventilation (the arrangement being that the device cannot start until the ventilation has started and 10 volumes of air have been purged from the enclosure) or be totally enclosed filled with inert gas. There is also a requirement for the type submerged in a liquid. (B) Class I, Division 2. In this location you can have open or nonexplosion-proof enclosed motors if they do not have brushes, switching mechanisms, or arc-producing devices. If they do have brushes, switching mechanisms, or arc-producing devices, the motor or generator must be identified for Class I, Division 1, locations or the devices must be in Class I, Division 1 identified enclosures as per Section 501.105(B). A requirement is noted for the surface temperature of space heaters used to prevent condensation. There are other specific requirements.
(A) Class I, Division 1. The entire fixture assembly must be identified for a Class I, Division 1 location and be protected against physical damage. Pendant luminaires (fixtures) must be wired and hung through rigid metal conduit or threaded steel intermediate conduit. Stems longer than 300 mm (12 in.) must have additional lateral bracing not more than 300 mm (12 in.) from the end of the stem or a flexible fitting approved for a Class I, Division 1 location. All boxes, fittings, etc., must be identified for Class I, Division 1 locations. (B) Class I, Division 2. Portable lighting equipment must comply with Class I, Division 1 requirements. There is an exception when it is mounted on a moveable stand and connected by flexible cord. Fixed lighting must be protected against physical damage. If there is danger of falling sparks or hot metal igniting vapors or gases, proper enclosures must be provided. If the operating temperature will exceed 80% of the ignition temperature of the gases or vapors, they must comply with Section 501.130(A)(1) or be of the type that has been tested to determine the temperature range or operating temperature marked. Pendant luminaires (fixtures) have the same rules as Class I, Division 1 locations. Switches must be in accordance with Section 501.6(B)(1). Starting equipment for electric-discharge lamps must be in accordance with Section 501.7(B) unless it is part of a "thermally protected fluorescent lamp ballast" and the lighting fixture has been identified for this location.
These are permitted only to connect the portable equipment to the fixed part of the system. They can also be used under certain conditions where a greater degree of movement is needed. As such, they must be identified for extra hard usage, contain a grounding conductor, be connected to the supply conductors or terminals in an approved way, ensure that there is no tension applied, and be provided with seals where necessary. Exceptions are made in Sections 501.10(B) and 501.105(B)(6). There is additional information concerning electrical submersible pumps and electric mixers.
Must be of the grounding type and approved for Class I locations except as provided in Section 501.105(B)(6).
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I. General
This article refers to areas classified as Class II. Explosion-proof equipment cannot be required and used unless identified for Class II locations. II. Wiring (A) Class II, Division 1. Only threaded rigid metal conduit, threaded steel intermediate metal conduit, Type MI cable can be used. Boxes and fittings can have no openings and have threaded bosses so that no dust can come in. If used where the dust is combustible electrically conductive, they must be approved for Class II locations. If a flexible connection must be used, it has to be either a dust-tight flexible connector, liquidtight flexible metal conduit, liquidtight non-metallic conduit, certain types of interlocked armor type MC cable with certain requirements, or a flexible cord for extra-hard usage and bushed fittings. The flexible cord must comply with section 502.140. There is an exception for certain industrial establishments. (B) Class II, Division 2. Methods permitted are rigid metal conduit, intermediate metal conduit, electrical metal tubing, dust-tight wireways, or Type MI or MC cable that have listed termination fittings or Type PLTC, MC, ITC, or TC cable, all under certain conditions. There is an exception. Also, wireways, fittings, and boxes must be dust tight. The requirements for flexible connections are noted in 502.10(A)(2). There are additional requirements.
If a raceway connects two enclosures, one being dust-ignition-proof, the other not, provision must be made to prevent dust from getting into the dust-ignition-proof enclosures. This can be done with seals, a minimum of 3.05 m (10 ft.) of horizontal raceway, or a minimum of 1.5 m (5 ft.) of vertical raceway or a raceway extending only horizontally and downward from the dust-ignition proof enclosure and complying with the above requirements for horizontal or vertical raceways. If the dust-ignition-proof enclosure is connected to one in an unclassified area, a seal is not required.
There can be no uninsulated exposed parts such as conductors, buses, etc., that operate at more than 30 volts. This limit is reduced to 15 volts in wet locations. The protection must be in accordance with 500.7(E), 500.7(F), or 500.7(G).
Ground, in accordance with Article 250 and the requirements of 502.30(A) and (B), all wiring and equipment. (A) Bonding jumpers with proper fittings or other approved means must be used. Locknut bushings and double lock-nut contacts alone are not to be depended on. The means of bonding applies to all raceways, fittings, boxes, enclosures, etc., between Class II locations and the grounding point for service equipment or separately derived systems. There is an exception. (B) If flexible conduit is used, it must have internal or external bonding jumpers in parallel with each conduit. It must also comply with the requirements of Section 250.102. There is an exception.
III. Equipment
(A) Class II, Division 1
(B) Class II, Division 2
(A) Class II, Division 1. Their enclosures must be dust-ignition-proof. If the dust is a hazardous metal (magnesium, etc.), the enclosure must be identified for this specific type of location. If disconnecting and isolating switches are not installed where there is electrically conductive dust, are not to interrupt current, and have no fuses, the enclosure only has to be tight so as to keep the entrance of dust to a minimum and have no openings, as well as have close-fitting or telescoping covers. (B) Class II, Division 2. The enclosures only have to be dust-tight.
(A) Class II, Division 1. The enclosures must be dust-ignition-proof identified for a Class II location. If they are installed in a location with hazardous metal dust (magnesium, etc.), the enclosure must be identified for this specific type of location. (B) Class II, Division 2. In these locations, the switching mechanisms must have a dust-tight enclosure. If they are in the same location as the switching mechanism, they must have tight metal enclosures with no openings. Resistors must have identified Class II enclosures unless their temperature is not higher than 248°F and they are either nonadjustable or part of an automatic timing system. In that case the enclosures have only to be tight with no openings. There are other requirements.
(A) Class II, Division 1. They must be either totally enclosed pipe-ventilated and meet the temperature restrictions of Section 502.5 or be identified for locations classified as Class II, Division 1. (B) Class II, Division 2. They must be either totally enclosed pipe-ventilated, totally enclosed fan-cooled, totally enclosed waterair-cooled, totally enclosed nonventilated or dust-ignition-proof with full load external temperature in accordance with Section 500.8(C)(2). There are exceptions for these types of motors if the authority having jurisdiction feels that the machines are easily cleaned and maintained and there will not be a large accumulation of dust.
The piping must (1) be metal at least 0.53 mm (0.021 in.) thick or of noncombustible material of equal substance, (2) be screened at the outside ends, (3) lead to the outside of the building and have clean air available, and (4) be protected against corrosion and physical damage. In addition, it must comply with: (A) Class II, Division 1. The pipes must be entirely dust-tight. They must also be either riveted and soldered, bolted and soldered, welded, or be dust-tight by another effective means. (B) Class II, Division 2. The pipes must be tight enough to prevent the entrance of dust in appreciable quantities.
(A) Class II, Division 1. The luminaires (fixtures) must be identified for Class II locations and additionally for hazardous metal dust if so located. They must be protected against physical damage. Pendant fixtures must be suspended using threaded rigid metal conduit, threaded steel intermediate metal conduit, or approved chains or other means. If the stem is longer than 300 mm (12 in.), it must be braced within 300 mm (12 in.) from the lower end or have a flexible fitting not more than 300 mm (12 in.) from the upper end. If conduit is not used for the wiring, the cord must be listed for hard usage and proper seals must be used. All boxes, fittings, etc., must be identified for Class II locations. (B) Class II, Division 2. Portable lighting equipment must be identified for Class II locations. A fixed luminaire (lighting fixture) must only minimize the collection of dust and prevent the escape of sparks. It must also have maximum wattage permitted for temperatures in accordance with Section 500.8(C)(2). Luminaires (fixtures) in these locations must also be protected against physical damage. Requirements for pendant fixtures in Division 2 are basically the same as for Division 1. One difference is that seals are not required. The requirements of Section 502.120(B) apply here for starters and control equipment for electric-discharge lamps.
(A) Class II, Division 1. Must be identified for Class II locations. If hazardous dust is present, it must also be identified for that location. (B) Class II, Division 2. Heaters must be identified for Class II locations. There is one exception. Motors must be in accordance with Section 502.125(B). Dust-tight enclosures are required for circuit breakers, switches, and fuses. Section 502.120(B) is applied to transformers, impedance coils, and resistors.
(A) Class II, Division 1. Must be identified for Class II locations and have a grounding conductor connection. (B) Class II, Division 2. Must also have a grounding conductor connection. They cannot permit the supply circuit to open with exposed live parts.
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I. General
Maximum surface temperatures for equipment permitted under operating conditions are 165°C (329°F) for normal operation or 120°C (248°F) if the equipment can be overloaded. II. Wiring (A) Class III, Division 1. Use only rigid metal conduit, rigid nonmetallic conduit, intermediate metal conduit, electrical metallic tubing, dust-tight wireways or Type MI or MC cables with listed fittings. Fittings and boxes must be dust tight. Refer to this section for the requirements for flexible connections and nonincendive field wiring. (B) Class III, Division 2. Same requirements as Division 1. An exception is made for storage areas with no machinery, where open wire on insulators can be used complying with Article 398, specifically Section 398.15(C).
There can be no uninsulated exposed parts such as conductors, buses, etc., that operate at more than 30 volts. This limit is reduced to 15 volts in wet locations. The protection must be in accordance with 500.7(E), 500.7(F), or 500.7(G). There is an exception as provided in 503.155.
As per Article 250. Also, the same requirements hold true for bonding and grounding as in Sections 501.16, and 502.16. There are exceptions. Rules for equipment grounding conductors are noted. III. Equipment
Must be in accordance with Section 502.100(B).
These devices must have dust-tight metal enclosures.
Must be in dust-tight enclosures complying with temperature limitations in Section 503.5.
Must be totally enclosed pipe ventilated, totally enclosed non-ventilated, or totally enclosed fan cooled. There is an exception where the authority having jurisdiction will permit it.
Must be metal at least 533 mm (0.021 in.) thick or equal noncombustible material, have physical damage protection, go directly outside to clean air, and be screened. The pipes must be tight enough to prevent "appreciable quantities" of fibers or flyings from getting in and sparks getting out.
Protect against physical damage. Prevent entrance of fibers or flyings or escape of sparks. Pendant stems must be threaded rigid metal conduit, threaded intermediate metal conduit, or threaded metal tubing. Chains with approved fittings can be used for suspending fixtures. The same rules apply for bracing stems over 3.5 mm (12 in.) long as Class II. Portable lamps must have handles, guards, and the lampholders have no switches, exposed parts, or receptacles.
Heaters: identified for Class III locations. Motors: Section 503.125. Switches, circuit breakers, motor controllers, and fuses: 503.115.
They must be listed for extra-hard usage, have a grounding conductor, be connected in an approved manner, be supported so as to prevent tension on the connections, and have provisions to prevent fibers or flyings from entering the boxes or fittings.
They must be of the grounding type, and designed to prevent the escape of sparks or molten particles and minimize the entry of fibers or flyings. An exception is provided where permitted by the authority having jurisdiction.
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Article 505 Class I, Zone 0, 1, and 2 Locations If this article is used, the equipment selection, wiring methods, and area classification must be under the supervision of a qualified registered professional engineer.
Article 506 Zone 20, 21, and 22 Locations for Flammable Dusts, Fibers, and Flyings
Article 510 Hazardous (Classified) LocationsSpecific Articles 511 through 517 cover specific locations that might be hazardous. The following article titles are listed for reference: Article 511Commercial Garages, Repair and Storage; Article 513Aircraft Hangars; Article 514Motor Fuel Dispensing Facilities; Article 515Bulk Storage Plants; Article 516Spray Application, Dipping, and Coating Processes. Article 517 Health Care Facilities I. General FPN: Rules that are followed by a reference in brackets contain text that has been extracted from NFPA-2002, Standard for Health Care Facilities. Only editorial changes were made to the extracted text to make it consistent with the NEC. Electrical construction and installation criteria for health care facilities that provide service to human beings are covered in this article. Performance, maintenance, and testing criteria are covered in NFPA 99 and other appropriate health care documents. Veterinary facilities are not covered. The reader is referred to NFPA 99. Parts II and III are intended to be applied to both single-function buildings and to applicable portions of multifunction buildings. The example used is a doctor's examining room in a residential custodial care facility having to comply with Section 517.10. Many definitions are listed in this section that are not covered in Article 100. These are specific to health care facilities. The reader should refer to these in the Code. II. Wiring Design and Protection Generally, this part applies to all health care facilities. Part II does not apply to business offices, corridors, waiting rooms, and similar areas in clinics, medical and dental offices, and outpatient clinics, and if wired in accordance with Chapters 1, 2, 3, and 4 of the Code, patient sleeping areas in nursing homes and limited care facilities.
It is important that the system installed maintain low potential differences between exposed conductive surfaces which are likely to become energized and the patient could contact. All the requirements of Chapters 1 through 4 must be followed unless they are changed in this article.
(A) Wiring Methods. Branch circuits serving patient care areas must have a ground path for fault current by being installed in a metal raceway or cable having a metallic armor or sheath assembly which qualifies as an equipment grounding return path. This is in addition to all other requirements of this section. (B) Insulated Equipment Grounding Conductor. If operated over 100 V, the grounding terminal of all receptacles and noncurrent-carrying areas of fixed equipment that a person can contact and may become energized must be grounded using an insulated copper conductor. It must be sized according to Table 250.122 and be installed in a metal raceway or as a part of listed cables that have metallic armor or sheath assembly with the branch-circuit conductors supplying the equipment or receptacle. There are two exceptions.
The equipment grounding busses of all panelboards serving the same patient vicinity must be bonded together. This is to be done using a continuous insulated copper conductor 10 AWG or larger. If two or more panelboards serve the same patient vicinity and are served from different transfer switches in the emergency system, then the equipment grounding terminal buses have to be bonded together with an insulated continuous copper conductor. The conductor cannot be smaller than 10 AWG.
(A) Applicability. Hospitals and other buildings that have or provide essential utilities or services for critical care areas or use life support equipment must comply with 517.17. (B) Feeders. If ground-fault protection is used at the service disconnect as per Section 230.95 or 215.10, an additional step is needed at the next level of feeder away from the service. There are three areas listed where the additional level of ground- fault protection cannot be installed. (C) Selectivity. The system must be fully selective. Six-cycle separation between the levels is required. (D) Testing
(A) Patient Bed Location. Each patient bed location must have at least two branch circuits, at least one of them must originate from the normal system and one from the emergency system. All branch circuits on the normal system must come from the same panel-board. There are three exceptions to this. (B) Patient Bed Location Receptacles. Each location must have at least four receptacles, either single, duplex, or a combination. They must all be hospital grade and grounded with an insulated copper conductor in accordance with Table 250.122. There are two exceptions to this. (C) Pediatric Locations. The receptacles must be listed tamper resistant or have a listed tamper resistant cover.
(A) Patient Bed Location Branch Circuits. Each patient bed location must have at least two branch circuits, at least one from the normal system and one from the emergency system. One circuit on the emergency system that supplies no other bed location must be available at each bed location. All branch circuits from the normal system must come from one panelboard. The emergency receptacles must be identified and have the panelboard and circuit number of its supply noted. There are two exceptions. (B) Patient Bed Location Receptacles. Each location must have at least six receptacles, either single, duplex, or a combination of both. At least one must be connected to the normal system or an emergency system supplied by a different transfer switch than the other receptacles in that location. They must all be hospital grade and grounded with an insulated copper conductor to the reference grounding point. (C) Patient Vicinity Grounding and Bonding (Optional). A patient equipment grounding point is allowed in the patient vicinity. It can have grounding and bonding jacks listed for that purpose. All the grounding terminals on the receptacles must be connected to the patient equipment grounding point if supplied with an equipment bonding jumper no smaller than 10 AWG. This jumper can be looped or run centrically. (D) Panelboard Grounding. Grounding of panelboards and switchboards must be accomplished if a grounded distribution system is used and metal feeder raceway or Type MC or MI cable is used. There are three acceptable means noted for use at each termination or junction point in the system. (E) Additional Protective Techniques in Critical Care Areas (Optional). Isolated power systems are permitted. (F) Isolated Power System Grounding (G) Special-Purpose Receptacle Grounding (A) In a wet location two methods can be used to protect personnel. Either a ground-fault circuit interrupter can be used if power interruption is acceptable or an isolated power supply can be used. There is an exception. (B) Isolated power supplies must conform to Section 517.160.
Not required for receptacles in critical care areas that have the toilet and basin in the patient room. III. Essential Electrical System This system is needed to provide light and power for systems essential to life safety and orderly cessation of procedures during a power failure of the normal electrical supply. The types of structures and services are listed in the Code. The reader is also referred to NFPA 99-2002 for further information as to the need for an essential electrical system.
(A) Applicability (B) General. The system is comprised of two separate systems, the emergency system and the equipment system. The emergency systems has a life safety branch and a critical branch. The equipment system supplies power to major equipment. The number of transfer switches depends on many design considerations. One switch can be used for a system with a maximum demand of 150 kVA (120 kw). Loads not noted in Article 517 must have their own transfer switch and must not transfer if it overloads the generator and must automatically shed if the generating equipment becomes overloaded. Continguous facilities can be served by the hospital power and alternate power sources. [NFPA99, 13.3.4.3] (C) Wiring Requirements. The life safety and critical branch must be kept separate from all other wiring and equipment except for four conditions. The wiring of the emergency system must be mechanically protected. There are five methods accepted. When isolated power systems are used in anesthetizing locations or special environments, each must be supplied by a separate circuit. (D) Capacity of Systems. The system must be able to supply the entire load. There is now a statement on demand calculations. (E) Receptacle Identification. Must be distinctively marked. [NFPA99, 4.4.2.2.4.2(B)] This is divided into two required branches, the life safety and the critical. This system must be automatically restored to power within 10 seconds of the loss of the normal supply. [NFPA99, 4.4.2.2.2.1, 4.4.3.1]
The Code lists all the items that are required to be on the life safety branch. They are basically illumination of means of egress, exit signs, alarm and alerting systems, communication systems, generator set location, elevators, and automatic doors. The reader is referred to the Code for the exact list. No function other than those listed can be connected to the life safety branch. The Code lists all the items that are required to be on the critical branch. They are basically task illumination and selected receptacles for the isolated power system, anesthetizing locations, patient care areas, additional specialized areas, nurse call systems, blood, bone and tissue bank, telephone equipment room and closets, special areas, and special circuits. The critical branch can be divided into two or more branches. The reader is referred to the Code for the exact list.
This section describes what equipment must be placed on the equipment system. It also describes how the system is energized (i.e., automatic, delayed automatic, and manually). The reader is referred to the Code for the exact requirements. (A) Two Independent Sources of Power. There must be a normal source of power and an alternate source of power for use when the normal source is interrupted. [NFPA99, 4.4.1.1.4] (B) Alternate Source of Power. This must be located on the premises and be a generator driven by a prime mover, another generator when the normal source is a generator, or an outside utility company when the normal source is a generator. (C) Location of Essential Electrical System Components
(A) Applicability (B) Inpatient Hospital Care Facilities. If the facility provides inpatient hospital care, it must comply with the requirements of Part III, 517.30 through 517.35. (C) Facilities Contiguous with Hospitals. These can have their systems supplied by the hospital. The reader is again referred to NFPA 99-2002 for performance, maintenance, and testing requirements.
(A) General. The systems for nursing homes and limited care facilities must have two separate branches, the life safety branch and the critical branch. [NFPA99, FPN ANNEX A 4.5.2.2.1] (B) Transfer Switches. The number of transfer switches depends on design. One transfer switch is permitted if the load is not more than 150 kVA. [NFPA99, 4.5.2.2.1] (C) Capacity of System. The system must be capable of supplying the entire load, that is required on the essential electrical system. (D) Separation from Other Circuits. The life safety branch must be kept separate from all other wiring and equipment. There are three exceptions. (E) Receptacle Identification. The receptacles or cover plates must have a distinctive color or marking.
The life safety branch must be automatically restored to power after 10 seconds of loss of the normal source of supply. This branch is referred to as the emergency system in NFPA 99-2002. The life safety branch basically supplies power for illumination of means of egress, exit signs, alarm and alerting systems, communication systems, dining and recreation areas, generator set location, and elevators. Refer to the Code for complete requirements. No function other than those listed can be connected to the life safety branch. For elevators [NFPA99, 4.4.2.2.2.2(6) and 4.5.2.2.2(7)]
This section describes what must be connected to the critical branch and how it is to be energized from the essential electrical system (i.e., automatic, delayed automatic, or manual). (A) Two Independent Sources of Power. There must be a normal source of power and an alternate source of power for use when the normal source is interrupted. [NFPA99, 4.4.1.1.4] (B) Alternate Source of Power. This must be located on the premises and be a generator driven by a prime mover. There is an exception to this when the normal source is a generator. In that case the alternate source can be either another generator or an outside utility company. There is also an exception where battery units may be used in nursing homes or limited-care facilities meeting the requirements of Section 517.40(A), Exception. [NFPA99, 17.3.4.1, 18.3.4.1.1] (C) Location of Essential Electrical System Components
(A) Essential Electrical Distribution. A battery or generator system must be used for the essential electrical distribution system. [NFPA 99-2002] (B) Electrical Life Support Equipment. An essential electrical distribution system described in 517.30 through 517.35 must be used if electrical life support equipment is required. [NFPA 99: 14.3.4.2.1] (C) Critical Care Areas. An essential electrical distribution system as described in 527.30 through 517.35 must be used where critical care areas are located. [NFPA99, 14.3.4.2.2] (D) Power Systems. Battery systems must follow the requirements of Article 700 and generator systems must follow the requirements of 517.30 through 517.35. IV. Inhalation Anesthetizing Locations The reader is again referred to NFPA 99-2002.
These are classified as hazardous (classified) or other-than-hazardous (classified).
V. X-Ray Installations
VI. Communications, Signaling Systems, Data Systems, Fire Alarm Systems, and Systems Less than 120 Volts, Nominal
VII. Isolated Power Systems
(A) Installations (B) Line Isolation Monitor The following article titles are listed for reference: Article 518Assembly Occupancies; Article 520Theaters, Audience Areas of Motion Picture and Television Studios, Performance Areas, and Similar Locations; Article 525Carnivals, Circuses, Fairs, and Similar Events; Article 530Motion Picture and Television Studios and Similar Locations; Article 540Motion Picture Projection Rooms; Article 545Manufactured Buildings; Article 547Agricultural Buildings; Article 550Mobile Homes, Manufactured Homes, and Mobile Home Parks; Article 551Recreational Vehicles and Recreational Vehicle Parks; Article 552Park Trailers; Article 553Floating Buildings; Article 555Marinas and Boatyards; 590Temporary Installations.
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This article covers all types of wiring, equipment, grounding power supply, and equipment interconnect, in information technology equipment rooms. The reader can refer to this article as well as NFPA 75-1999 Standard for the Protection of Electronic Computer/Data Processing Equipment (whose rules this room must comply with) for further information.
Article 645 will apply if all the following are met: (1) Disconnecting means are provided that are in accordance with Section 645.10; (2) a separate HVAC system is provided for the room, or another system in another area is used if fire/smoke dampers which operate from smoke detectors and operate from a disconnecting means required by Section 645.10 are provided in the ducts at the point of entry into the room; (3) the information technology equipment is listed; (4) the room is occupied only by the personnel needed to operate and maintain the equipment; (5) fire-resistant-rated walls and floors and ceilings with protected openings are used to separate the area from other areas.
(A) The ampacity of the branch-circuit conductors supplying units must be at least 125% of the total connected load. (B) The data processing system can be connected to branch circuits using flexible cords and attachment plug caps not exceeding 4.5 m (15 ft.), or cord set assemblies. If a cord set assembly is used on the floor, it must be protected from physical damage. (C) Separate units can be interconnected with cables and cable assemblies. They must be listed for this use and protected from physical damage. (D) There are a number of rules for circuits, cables, and devices under a raised floor. Cables and receptacles are allowed to be installed under a raised floor. The area under the floor has to be accessible and the floor must be of proper construction. Branch-circuit conductors must be installed in rigid or intermediate metal conduit, rigid nonmetallic conduit, electrical metallic tubing, electrical nonmetallic tubing, metal wireway, surface metal raceway with a metal cover, nonmetallic surface raceway, nonmetallic wireway, flexible metal conduit, liquidtight flexible metal or nonmetallic conduit, Type MI cable, Type MC cable, or Type AC cable and installed in accordance with Section 300.11. The openings in the raised floor for cables have protection against abrasion to the cables and a means to minimize the debris that will fall onto the floor. The ventilation system underfloor must have smoke detection that will shut off the circulation of air when a fire or products of combustion are detected. Cables other than those listed above must be listed as type DP cable with adequate fire-resistance to be used under a raised floor. There are conditions where this is not required. Abandoned cables are permitted to remain if installed within a metal raceway (E) All cables and accessories that are part of or used for the equipment have to be properly secured in place.
All cables that go outside the room have to comply with the NEC®. Utilize Section 300.21 for rules applying to all penetrations of the fire-resistant separation of the room.
Disconnecting means must be provided for all system equipment, HVAC equipment and fire/smoke dampers. This can be one central one or separate ones for different types of equipment. The disconnects have to be grouped together, identified, and be accessible at the principal exit. The exception is for those installations under Article 685.
These are commonly referred to as UPS. These systems have to comply with Section 645.10. The disconnecting means must disconnect the battery from its load. There are two exceptions. All exposed noncurrent-carrying metallic parts of an information technology system has to be grounded as noted in Article 250 or be double insulated. If the derived power system is in listed equipment and supplies power to systems through cable assemblies or receptacles which are part of the equipment, it is not considered a separately derived system as per Section 250.20(D). If signal reference structures are installed, they have to be bonded to the equipment grounding system of the computer equipment. Each piece of system equipment supplied by a branch circuit must have a manufacturer's nameplate. The nameplate must show the maximum rated load in amperes, voltage, and frequency.
Multiple panelboards are permitted in a single cabinet provided there are no more than 42 overcurrent devices in each panelboard and the power distribution unit is listed for information technology application. The following article titles are listed for reference: Article 647Sensitive Electronic Equipment; Article 650Pipe Organs; Article 660X-Ray Equipment; Article 665Induction and Dielectric Heating Equipment; Article 668Electrolytic Cells; Article 669Electroplating; Article 670Industrial Machinery; Article 675Electrically Driven or Controlled Irrigation Machines; Article 680Swimming Pools, Fountains, and Similar Installations; Article 682Natural and Artificially Made Bodies of Water; Article 685Integrated Electrical Systems; Article 690Solar Photovoltaic Systems; Article 692Fuel Cell Systems; Article 695Fire Pumps. Page 9
A. General This article lays out the electrical safety requirements for the installation, operation, and maintenance of emergency systems. Emergency systems include all items necessary to deliver electricity to the load. Emergency systems are defined as those which are legally required by any governmental agency or specific code that has jurisdiction. They supply, distribute, and control electricity for power and illumination which is essential for safety to human life. The code goes into detail with specific types of occupancies and equipment. The reader is referred to other articles in this code or to other NFPA documents for additional information as follows:
These additional documents and articles may place other restrictions on the design of the emergency system for the specific application of the document or article.
All applicable articles of the NEC® apply unless they are modified by this Article. All equipment must be approved for this use.
(A) Conduct or Witness Test. The system must be tested at installation and periodically thereafter. The test must be conducted and witnessed by the authority having jurisdiction. (B) Tested Periodically. To assure proper maintenance and operation the system must be tested on a schedule accepted by the authority having jurisdiction. (C) Battery System Maintenance. Batteries, whether for systems or in conjunction with engines, must be maintained periodically. (D) Written Record. A written record must be kept of all tests and maintenance. (E) Testing under Load. Provisions must be made to test the system under the maximum anticipated load. (A) Capacity and Rating. The system must be able to supply the entire load operating together. It must also be able to withstand the maximum available fault current. (B) Selective Load Pickup, Load Shedding, and Peak Load Shaving. This permits the system to be used for various levels of loads and peak shaving provided that it can supply the emergency circuits, the legally required standby circuits, and the optional standby circuits when required. The transfer equipment must be automatic. Interconnection of the normal and emergency sources must be prevented. Bypass means for isolation of the transfer switch are permitted. Automatic transfer switches must be electrically operated and mechanically held. Transfer equipment can supply only emergency loads. Audible and visual signal must be installed where practical to indicate the derangement of the emergency source, that the battery is carrying the load, the battery charger is not functioning, and there is a ground fault in solidly grounded wye systems of more than 150 V to ground and circuit protective devices rated more than 1000 A. There is additional information concerning the ground-fault devices. II. Circuit Wiring
(A) Identification. All items in the system must be readily identified as part of the system. (B) Wiring. The wiring of the system must be separate from the wiring of the normal system and cannot be in the same raceway, boxes, cabinets, cables, etc. There are four exceptions. (C) Wiring Design and Location. The circuits must be designed and located to reduce to a minimum the hazards due to flooding, vandalism, icing, fires, and other adverse conditions. (D) Fire Protection. Additional requirements are noted. III. Sources of Power
The current must be available for use within 10 seconds after the loss of normal power. The supply source can be any of the following: storage batteries, generator set, separate service, uninterruptible power supply, fuel cell system, and unit equipment. Each one is covered in the code in detail as to specific requirements. Again it must be noted that some of these may not be permitted for specific occupancies as noted in other documents (i.e., health care facilities). The equipment must be designed and located so that hazards from flooding, vandalism, icing, and fires are minimized. There are requirements for buildings with certain sizes and equipment. There are also additional requirements for storage batteries, generator set, uninterruptible power supplies, fuel cell system, separate service, and unit equipment. IV. Emergency System Circuits for Lighting and Power
Only those appliances and lamps needed for emergency use can be connected to the emergency lighting circuits.
V. ControlEmergency Lighting Circuits
VI. Overcurrent Protection
This is not required for the alternate source. Ground fault indication is required in accordance with Section 700.7(D). Page 10
A. General This article lays out the electrical safety requirements for the installation, operation, and maintenance of legally required standby power systems. This includes all equipment necessary to deliver power to the load. The reader is referred to NFPA 99-2002 (ANSI) Standard for Health Care Facilities for additional information, NFPA 110-2002 (ANSI) Emergency and Standby Power Systems for performance information, and to ANSI/IEEE 446-1995 Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications for further information. These are systems that have this classification set by any governmental agency having jurisdiction. They are intended to supply power automatically to selected loads other than emergency system loads if the normal source fails. They differ from emergency systems in that they are not required for direct safety to life. They do supply power where the interruption might create a hazard or hamper rescue or firefighting operations. Some examples are given in the code to help the reader.
Applicable articles of the Code apply unless otherwise modified in this Article. Items must be approved for this use.
(A) Conduct or Witness Test. When the installation is complete the authority having jurisdiction must either conduct or witness a test. (B) Tested Periodically. To assure proper maintenance and operation the system must be tested on a schedule accepted by the authority having jurisdiction. (C) Battery Systems Maintenance. Periodic maintenance is required if the batteries are used for control, starting, or ignition of a prime mover. (D) Written Record. A written record must be kept of all tests and maintenance. (E) Testing under Load. Provisions must be made for testing under load.
The system must be able to supply the entire load operating together. It must also be able to withstand the available fault current. The transfer equipment must be automatic, identified for standby use, and approved by the authority having jurisdiction. Interconnection of the normal and emergency sources must be prevented. Bypass means for isolation of the transfer switch is permitted. Automatic transfer switches have to be electrically operated and mechanically held. Audible and visual signals must be provided to indicate the derangement of the standby source, that the standby source is carrying the load, and that the battery charger is not functioning. The type and location of the system must be indicated on a sign at the service entrance. There is an exception for certain unit equipment. If the system is grounded to a remote grounding electrode a sign must be placed at the grounding location identifying all emergency and normal sources connected there. II. Circuit Wiring
The wiring for this system can occupy the raceways, cables, boxes, cabinets, etc. as the general wiring. III. Sources of Power
The current must be available for use within 60 seconds of the loss of the normal power. The supply system can be any one of the following: storage battery, generator set, uninterruptible power supply, separate service, connection ahead of the service disconnecting means, fuel cell system, and unit equipment. Each is covered in the code in detail as to specific requirements. Again it must be noted that some of these may not be permitted for specific occupancies as noted in other documents (i.e., health care facilities). VI. Overcurrent Protection
This is not required for the alternate source. The system must be selectively coordinated with the supply side overcurrent protection devices. Page 11
I. General This article applies only to the installation and operation of optional standby systems. These systems protect business or property where life safety is not dependent on the system. Power can be supplied either automatically or manually.
Unless modified by this article, all provisions of the Code apply. All equipment must be approved for this use.
The system must be able to supply the entire load operating together. It must also be able to withstand the available fault current. The user can select the load which is connected to the system. Transfer equipment must be suitable for its use and designed and installed to prevent the inadvertent interconnection of the normal and alternate sources of power. If it is located on the load side of branch-circuit protection, it can have supplementary overcurrent protection with an interrupting rating that can handle the generator available fault current. There is an exception for temporary connection of a portable generator. Audible and visual signals must be provided to indicate the derangement of the standby source and that the standby source is carrying the load. The type and location of the system must be indicated on a sign at the service entrance. There is an exception for certain unit equipment. If the system is grounded to a remote grounding electrode a sign must be placed at the grounding location identifying all optional standby power and normal sources connected there. II. Circuit Wiring
The wiring for this system can occupy the raceways, cables, boxes, etc., as the general wiring. III. Grounding
(A) Separately Derived System. Must be grounded to a grounding electrode in accordance with 250.30. (B) Nonseparately Derived System. It must be bonded to the system grounding electrode. IV. Sources of Power
The following article titles are listed for reference: Article 705Interconnected Electric Power Production Sources; Article 720Circuits and Equipment Operating at Less Than 50 Volts; Article 725Class 1, Class 2, and Class 3 Remote-Control, Signaling, and Power-Limited Circuits; Article 727Instrumentation Tray Cable, Type ITC; Article 760Fire Alarm Systems; Article 770Optical Fiber Cables and Raceways; Article 780Closed-Loop and Programmed Power Distribution. Page 12
FPN No. 1: Table 1 is based on common conditions of proper cabling and alignment of conductors where the length of the pull and the number of bends are within reasonable limits. It should be recognized that, for certain conditions, a larger size conduit or a lesser conduit fill should be considered.
FPN No. 2: When pulling three conductors or cables into a raceway, if the ratio of the raceway (inside diameter) to the conductor or cable (outside diameter) is between 2.8 and 3.2, jamming can occur. While jamming can occur when pulling four or more conductors or cables into a raceway, the probability is very low.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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(1) See Appendix C for the maximum number of conductors and fixture wires, all of the same size (total cross-sectional area including insulation) permitted in trade sizes of the applicable conduit or tubing. (2) Table 1 applies only to complete conduit or tubing systems and is not intended to apply to sections of conduit or tubing used to protect exposed wiring from physical damage. (3) Equipment grounding or bonding conductors, where installed, shall be included when calculating conduit or tubing fill. The actual dimensions of the equipment grounding or bonding conductor (insulated or bare) shall be used in the calculation. (4) Where conduit or tubing nipples having a maximum length not to exceed 600 mm (24 inches) are installed between boxes, cabinets, and similar enclosures, the nipples shall be permitted to be filled to 60 percent of their total cross-sectional area, and Section 310.15(B)(2)(a) need not apply to this condition. (5) For conductors not included in Chapter 9, such as multi-conductor cables, the actual dimensions shall be used. (6) For combinations of conductors of different sizes, use Tables 5 and 5A for dimensions of conductors and Table 4 for the applicable conduit or tubing dimensions. Table 4. Dimensions and Percent Area of Conduit and Tubing (Areas of Conduit or Tubing for the Combinations of Wires Permitted in Table 1, Chapter 9)  [View Full Width] [View Full Width] [View Full Width] [View Full Width] [View Full Width]
[View Full Width]
[View Full Width] [View Full Width] [View Full Width] [View Full Width] [View Full Width] [View Full Width] (7) When calculating the maximum number of conductors permitted in a conduit or tubing, all of the same size (total cross-sectional area including insulation), the next higher whole number shall be used to determine the maximum number of conductors permitted when the calculation results in a decimal of 0.8 or larger. (8) Where bare conductors are permitted by other sections of this Code, the dimensions for bare conductors in Table 8 shall be permitted. (9) A multiconductor cable of two or more conductors shall be treated as a single conductor for calculating percentage conduit fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.
Table 5A. Compact Aluminum Building Wire Nominal Dimensions[*] and Areas [View Full Width]
Table 8. Conductor Properties [View Full Width] Table 9. Alternating-Current Resistance and Reactance for 600-Volt Cables, 3-Phase, 60 Hz, 75°C (167°F)Three Single Conductors in Conduit [View Full Width] Page 14
For listing purposes, Tables 11(A) and 11(B) provide the required power source limitations for Class 2 and Class 3 power sources. Table 11(A) applies for alternating-current sources, and Table 11(B) applies for direct-current sources. The power for Class 2 and Class 3 circuits shall be either (1) inherently limited requiring no overcurrent protection, or (2) not inherently limited requiring a combination of power source and overcurrent protection. Power sources designed for interconnnection shall be listed for the purpose. As part of the listing, the Class 2 or Class 3 power source shall be durably marked where plainly visible to indicate the class of supply and its electrical rating. A Class 2 power source not suitable for wet location use shall be so marked. Exception: limited power circuits used by listed information technology equipment. Overcurrent devices, where required, shall be located at the point where the conductor to be protected receives its supply and shall not be interchangeable with devices of higher ratings. The overcurrent device shall be permitted as an integral part of the power source.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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Note 1. Vmax, Imax, and VAmax are determined with the current limiting impedance in the circuit (not bypassed) as follows: Vmax: Maximum output voltage regardless of load with rated input applied. Imax: Maximum output current under any noncapacitive load, including short circuit, and with overcurrent protection bypassed if used. Where a transformer limits the output current, Imax limits apply after one minute of operation. Where a current-limiting impedance, listed for the purpose, or as part of a listed product, is used in combination with a nonpower-limited transformer or a stored energy source, e.g., storage battery, to limit the output current, Imax limits apply after five seconds. VAmax: Maximum volt-ampere output after one minute of operation regardless of load and overcurrent protection bypassed if used. Note 2. For nonsinusoidal ac, Vmax shall be not greater than 42.4 volts peak. Where wet contact (immersion not included) is likely to occur, Class 3 wiring methods shall be used or Vmax shall be not greater than 15 volts for sinusoidal ac and 21.2 volts peak for nonsinusoidal ac. Note 3. If the power source is a transformer, (VA)max is 350 or less when Vmax is 15 or less. Note 4. For dc interrupted at a rate of 10 to 200 Hz, Vmax shall not be greater than 24.8 volts peak. Where wet contact (immersion not included) is likely to occur, Class 3 wiring methods shall be used or Vmax shall not be greater than 30 volts for continuous dc; 12.4 volts peak for dc that is interrupted at a rate of 10 to 200 Hz.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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For listing purposes, Tables 12(A) and 12(B) provide the required power source limitations for power-limited fire alarm sources. Table 12(A) applies for alternating current sources, and Table 12(B) applies for direct current sources. The power for power-limited fire alarm circuits shall be either (1) inherently limited requiring no overcurrent protection, or (2) not inherently limited requiring the power to be limited by a combination of power source and overcurrent protection. As part of the listing, the PLFA power source shall be durably marked where plainly visible to indicate that it is a power-limited fire alarm power source. The overcurrent device, where required, shall be located at the point where the conductor to be protected receives its supply and shall not be interchangeable with devices of higher ratings. The overcurrent device shall be permitted as an integral part of the power source.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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Note 1: Vmax, Imax, and VAmax are determined as follows: Vmax: Maximum output voltage regardless of load with rated input applied. Imax: Maximum output current under any noncapacitive load, including short circuit, and with overcurrent protection bypassed if used. When a transformer limits the output current, Imax limits apply after one minute of operation. Where a current-limiting impedance, listed for the purpose, is used in combination with a nonpower-limited transformer or a stored energy source, e.g., storage battery, to limit the output current, Imax limits apply after five seconds. Table 11(A). Class 2 and Class 3 Alternating-Current Power Source Limitations [View Full Width]
Table 11(B). Class 2 and Class 3 Direct Current Power Source Limitations [View Full Width]
Table 12(A). Table PLFA Alternating-Current Power Source Limitations [View Full Width] Table 12(B). PLFA Direct-Current Power Source Limitations [View Full Width] VAmax: Maximum volt-ampere output after one minute of operation regardless of load and overcurrent protection bypassed if used. Current limiting impedance shall not be bypassed when determining Imax and VAmax. Note 2. If the power source is a transformer, (VA)max is 350 or less when Vmax is 15 or less.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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This Annex is not part of the requirements of the NFPA document but is listed for informational purposes. Reprinted with permission from NFPA 70-2005, the National Electrical Code®, Copyright © 2004, National Fire Protection Association, Quincy, MA 02269. This reprinted material is not the referenced subject which is represented only by the standard in its entirety.
Table C1. Maximum Number of Conductors or Fixture Wires in Electrical Metallic Tubing (EMT) (Based on Table 1, Chapter 9) [View Full Width]
Table C1(A). Maximum Number of Compact Conductors in Electrical Metallic Tubing (EMT) (Based on Table 1, Chapter 9) [View Full Width]
Table C3. Maximum Number of Conductors or Fixture Wires in Flexible Metal Conduit (FMC) (Based on Table 1, Chapter 9) [View Full Width]
Table C3(A). Maximum Number of Compact Conductors in Flexible Metal Conduit (FMC) (Based on Table 1, Chapter 9) [View Full Width] Table C4. Maximum Number of Conductors or Fixture Wires in Intermediate Metal Conduit (IMC) (Based on Table 1, Chapter 9) [View Full Width]
Table C4(A). Maximum Number of Compact Conductors in Intermediate Metal Conduit (IMC) (Based on Table 1, Chapter 9) [View Full Width]
Table C7. Maximum Number of Conductors or Fixture Wires in Liquidtight Flexible Metal Conduit (LFMC) (Based on Table 1, Chapter 9) [View Full Width]
Table C7(A). Maximum Number of Compact Conductors in Liquidtight Flexible Metal Conduit (LFMC) (Based on Table 1, Chapter 9) [View Full Width] Table C8. Maximum Number of Conductors or Fixture Wires in Rigid Metal Conduit (RMC) (Based on Table 1, Chapter 9) [View Full Width]
Table C8(A). Maximum Number of Compact Conductors in Rigid Metal Conduit (RMC) (Based on Table 1, Chapter 9) [View Full Width] Table C9. Maximum Number of Conductors or Fixture Wires in Rigid PVC Conduit, Schedule 80 (Based on Table 1, Chapter 9) [View Full Width]
Table C9(A). Maximum Number of Compact Conductors in Rigid PVC Conduit, Schedule 80 (Based on Table 1, Chapter 9) [View Full Width] Table C10. Maximum Number of Conductors or Fixture Wires in Rigid PVC Conduit, Schedule 40 and HDPE Conduit (Based on Table 1, Chapter 9) [View Full Width]
Table C10(A). Maximum Number of Compact Conductors in Rigid PVC Conduit, Schedule 40 and HDPE Conduit (Based on Table 1, Chapter 9) [View Full Width] Table C11. Maximum Number of Conductors or Fixture Wires in Type A, Rigid PVC Conduit (Based on Table 1, Chapter 9) [View Full Width]
Table C11(A). Maximum Number of Compact Conductors in Type A, Rigid PVC Conduit (Based on Table 1, Chapter 9) [View Full Width]
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This annex is not part of the requirements of the NFPA document but is included for informational purposes. Selection of Conductors. In the following examples, the results are generally expressed in amperes (A). To select conductor sizes, refer to the 0 through 2000 Volt (V) ampacity tables of Article 310 and the rules of 310.15 that pertain to these tables. Voltage. For uniform application of Articles 210, 215, and 220, a nominal voltage of 120, 120/240, 240, and 208Y/120 volts shall be used in calculating the ampere load on the conductor. Fractions of an Ampere. Except where the calculations result in a major fraction of an ampere (0.5 or larger), such fractions are permitted to be dropped. Power Factor. Calculations in the following examples are based, for convenience, on the assumption that all loads have the same power factor (PF). Ranges. For the calculation of the range loads in these examples, Column C of Table 220.55 has been used. For optional methods, see Columns A and B of Table 220.55. Except where the calculations result in a major fraction of a kilowatt (0.5 or larger), such fractions are permitted to be dropped. SI Units. For metric conversions, 0.093 m2 = 1 ft2 and 0.3048 m = 1 ft.
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Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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The dwelling has a floor area of 1500 square feet exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. Appliances are a 12-kW range and a 5.5-kW, 240-volt dryer. Assume range and dryer kW ratings equivalent to kVA ratings in accordance with Sections 220.54 and 220.55. Calculated Load [See 220.40] General lighting load: 1500 sq. ft. at 3 volt-amperes per sq. ft. = 4500 volt-amperes. Minimum Number of Branch Circuits Required [See Sec-tion 210.11(A)] General lighting load: 4500 volt-amperes ÷ 120 V = 37.5 A. This requires three 15-A, 2-wire or two 20-A, 2-wire circuits. Small appliance load: two 2-wire, 20-A circuits [see 210.11(C)(1)]. Laundry load: one 2-wire 20-A circuit [see 210.11(C)(2)]. Bathroom branch circuit: One 2-wire, 20-A circuit (no additional calculation is required for this circuit) [see 210.11(C)(3)]. Minimum Size Feeder Required [See 220.40]
Net calculated load for 120/240-volt 3-wire single-phase service or feeder Sections 230.42(B) and 230.79 require service conductors and disconnecting means rated not less than 100 amperes. Calculation for Neutral for Feeder and Service
Calculated Load for Neutral
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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Assume same conditions as Example No. D1(a), plus addition of one 6-ampere, 230-volt room air-conditioning unit and one 12-ampere, 115-volt room air-conditioning unit,* one 8-ampere, 115-volt rated waste disposer, and one 10-ampere, 120-volt rated dishwasher. See Article 430 for general motors and Article 440, Part VII, for air-conditioning equipment. Motors have nameplate ratings of 115 V and 230 V for use on 120-V and 240-V nominal voltage systems. From Example No. D1(a), feeder current is 78 amperes (3-wire 240 volts).
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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The dwelling has a floor area of 1500 square feet exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has a 12-kW range, a 2.5-kW water heater, a 1.2-kW dishwasher, 9 kW of electric space heating installed in five rooms, a 5-kW clothes dryer, and a 6-ampere, 230-volt room air-conditioning unit. Assume range, water heater, dishwasher, space heating, and clothes dryer kW ratings equivalent to kVA. Air conditioner kVA calculation is 6A x 230V ÷ 1000 = 1.38 kVA This 1.38 kVA [Item 1 from 220.82(C)] is less than 40% of 9 kVA of separately controlled electric heat [Item 6 from 220.82(C)], so the 1.38 kVA need not be included in the service calculation.
Application of Demand Factor [See 220.82(B)]
Calculated load for service size Therefore, the minimum service size would be 100 amperes in accordance with 230.42 and 230.79.
Calculated Load for Neutral
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Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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The dwelling has a floor area of 1500 square feet exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has two 20-ampere small appliance circuits, one 20-ampere laundry circuit, two 4-kW wall-mounted ovens, one 5.1-kW counter-mounted cooking unit, a 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW combination clothes washer and dryer, six 7-ampere, 230-volt room air-conditioning units, and a 1.5-kW permanently installed bathroom space heater. Assume wall-mounted ovens, counter-mounted cooking unit, water heater, dishwasher, and combination clothes washer and dryer kW ratings equivalent to kVA. Air Conditioning kVA Calculation Load Included at 100% Air conditioning: Included below [See Item 1 in 220.82(C)] Space heater: Omit [See Item 5 in 220.82(C)]
Calculated Load for Service Feeder Neutral Load (per 220.61) Assume that the two 4-kVA wall-mounted ovens are supplied by one branch circuit, the 5.1-kVA counter-mounted cooking unit by a separate circuit.
Two 4-kVA ovens plus one 5.1-kVA cooking unit = 13.1 kVA. Table 220.55 permits 55% demand factor or
Calculated Load for Neutral
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Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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Dwelling has a floor area of 2000 sq. ft. exclusive of an unfinished cellar not adaptable for future use, unfinished attic, and open porches. It has a 12-kW range, 4.5-kW water heater, a 1.2-kW dishwasher, a 5-kW clothes dryer, a 2 ½-ton (24-ampere) heat pump with 15-kW of back-up heat. Heat Pump kVA Calculation This 5.76 kVA is less than 15 kVA of the backup heat; therefore, the heat pump load need not be included in the service calculation. [See 220.82(C).]
Calculated Load for Service Therefore, this dwelling unit may be served by a 150-ampere service.
Article 90 Introduction General Wiring and Protection Wiring Methods and Materials Equipment for General Use Special Occupancies Special Equipment
Special Conditions Tables Annex C. Conduit and Tubing Fill Tables for Conductors and Fixture Wires of the Same Size Annex D. Examples
Annex E. Types of Construction
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A store 50 ft. by 60 ft., or 3000 sq. ft., has 30 ft. of show window. There are a total of 80 duplex receptacles. The service is 120/240-volt, single-phase 3-wire service. Actual connected lighting load, 8500 volt-amperes.
Minimum Number of Branch Circuits Required General Lighting: Branch circuits need only be installed to supply the actual connected load [see 221.11(B)].
The lighting load would be permitted to be served by 2-wire or 3-wire, 15- or 20-ampere circuits with combined capacity equal to 44 amperes or greater for 3-wire circuits or 88 amperes or greater for 2-wire circuits. The feeder capacity as well as the number of branch-circuit positions available for lighting circuits in the panelboard must reflect the full calculated load of 9000 VA x 1.25 = 11,250 volt-amperes. Show Window
The show window lighting is permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 31 amperes or greater for 3-wire circuits or 62 amperes or greater for 2-wire circuits. Receptacles required by 210.62 are assumed to be included in the receptacle load above if these receptacles do not supply the show window lighting load. Receptacles
The receptacle load would be permitted to be served by 2-wire or 3-wire circuits with a capacity equal to 60 amperes or greater for 3-wire circuits or 120 amperes or greater for 2-wire circuits. Minimum Size Feeder (or Service) Overcurrent Protection [See 215.3 or Section 230.90]
The next higher standard size is 150 amperes (See 240.6). Minimum Size Feeder (or Service Conductors) Required [See 215.2, 230.42(A)] For 120/240-volt, 3-wire system: 32,450 volt-amperes ÷ 240 volts = 135 amperes.
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An industrial multi-building facility has its service at the rear of its main building, and then provides 480Y/277-volt feeders to additional buildings behind the main building in order to segregate certain processes. The facility supplies its remote buildings through a partially enclosed access corridor that extends from the main switchboard rearward along a path that provides convenient access to services within 15 m (50 ft) of each additional building supplied. Two building feeders share a common raceway for approximately 45 m (150 ft) and run in the access corridor along with process steam and control and communications cabling. The steam raises the ambient temperature around the power raceway to as much as 35°C. At a tee fitting, the individual building feeders then run to each of the two buildings involved. The feeder neutrals are not connected to the equipment grounding conductors in the remote buildings. All distribution equipment terminations are listed as being suitable for 75°C connections.
By using 430.24, the motor loads and the noncontinuous loads can be combined for the remaining calculation.
The overcurrent protective device must accommodate 125% of the continuous load, plus the noncontinuous load:
Where the overcurrent protective device and its assembly are listed for operation at 100 percent of its rating, a 125 ampere overcurrent protective device would be permitted. However, overcurrent protective device assemblies listed for 100 percent of their rating are typically not available at the 125-ampere rating. (See 215.3 Exception.) Ungrounded Feeder Conductors The conductors must independently meet requirements for (1) terminations, and (2) conditions of use throughout the raceway run. Minimum size conductor at the overcurrent device termination [see 110.14(C) and 215.2(A)(1), using 75°C ampacity column in Table 310.16]: 1/0 AWG. Minimum size conductors in the raceway based on actual load [see Article 100, Ampacity, and 310.15(B)(2)(a) and correction factors to Table 310.16]: 99,000 VA / 0.7 / 0.96 = 147,000 VA (70% = 310.15(B)(2)(a)) & (0.96 = Correction factors to Table 310.16) Conversion to amperes: 147,000 VA / (480V x images/ent/U221A.GIF border=0>3) = 177A Note that the neutral conductors are counted as current-carrying conductors [see 310.15(B)(4)(c)] in the example because the discharge lighting has substantial nonlinear content. This requires a 2/0 AWG conductor based on the 90°C column of Table 310.16. Therefore, the worst case is given by the raceway conditions, and 2/0 AWG conductors must be used. If the utility corridor was at normal temperatures [(30°C (86°F)], and if the lighting at each building were supplied from the local separately derived system (thus requiring no neutrals in the supply feeders) the raceway result (99,000 VA / 0.8 = 124,000 VA; 124,000 VA / (480V x images/ent/U221A.GIF border=0>3) = 149 A, or a 1 AWG conductor @ 90°C) could not be used because the termination result (1/0 AWG based on the 75°C column of Table 310.16) would become the worst case, requiring the larger conductor. In every case, the overcurrent protective device shall provide overcurrent protection for the feeder conductors in accordance with their ampacity as provided by this Code (see 240.4). A 90°C 2/0 AWG conductor has a Table 310.16 ampacity of 195 amperes. Adjusting for the conditions of use (35°C ambient temperature, 8 current-carrying conductors in the common raceway), 195 amperes x 0.96 x 0.7 = 131 A The 150-ampere circuit breaker protects the 2/0 AWG feeder conductors, because 240.4(B) permits the use of the next higher standard size overcurrent protective device. Note that the feeder layout precludes the application of 310.15(A)(2) Exception. Feeder Neutral Conductor (see 220.61) Because 210.11(B) does not apply to these buildings, the load cannot be assumed to be evenly distributed across phases. Therefore the maximum imbalance must be assumed to be the full lighting load in this case, or 11,600 VA. (11,600 VA / 277V = 42 amperes.) The ability of the neutral to return fault current [see 250.32(B)(2)(2)] is not a factor in this calculation. Although the neutral runs between the main switchboard and the building panelboard, likely terminating on a busbar at both locations, the busbar connections are part of listed devices and are not "separately installed pressure devices." Therefore 110.14(C)(2) does not apply, and the normal termination temperature limits apply. In addition, the listing requirement to gain exemption from the additional sizing allowance under continuous loading (see 215.3 Exception) covers not just the overcurrent protective device, but its entire assembly as well. Therefore, since the lighting load is continuous, the minimum conductor size is based on 1.25 x (11,600 VA/277V) = 52 amperes, to be evaluated under the 75°C column of Table 310.16. The minimum size of the neutral is 6 AWG. This size is also the minimum size required by 215.2(A)(1), because the minimum size equipment grounding conductor for a 150-ampere circuit, as covered in Table 250.122, is 6 AWG. |
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