Article 445


445.1 Scope. This article contains installation and other requirements for generators.

  1. Location. Generators shall be of a type suitable for the locations in which they are installed. They shall also meet the requirements for motors in 430.14.
    Informational Note: See NFPA 37, Standard for the Installation andUse of Stationary Combustion Engines and Gas Turbines, for informa‐ tion on the location of generator exhaust.
  1. Marking. Each generator shall be provided with a nameplate giving the manufacturer’s name, the rated frequency, the number of phases if ac, the rating in kilowatts or kilovolt-amperes, the power factor, the normal volts and amperes corresponding to the rating, the rated ambient temperature, and the rated temperature rise.Nameplates or manufacturer’s instructions shall provide the following information for all stationary generators and portable generators rated more than 15 kW:
    1. Subtransient, transient, synchronous, and zero sequencereactances
    2. Power rating category
    3. Insulation system class
    4. Indication if the generator is protected against overload by inherent design, an overcurrent protective relay, circuit breaker, or fuse
    5. Maximum short-circuit current for inverter-based genera‐ tors, in lieu of the synchronous, subtransient, and transi‐ ent reactances
    Marking shall be provided by the manufacturer to indicate whether or not the generator neutral is bonded to its frame. Where the bonding is modified in the field, additional marking shall be required to indicate whether the neutral is bonded to the frame.
  2. Overcurrent Protection.
    1. Constant-Voltage Generators. Constant-voltage genera‐ tors, except ac generator exciters, shall be protected from over‐ load by inherent design, circuit breakers, fuses, protective relays, or other identified overcurrent protective means suita‐ ble for the conditions of use.
    2. Two-Wire Generators. Two-wire, dc generators shall be permitted to have overcurrent protection in one conductor only if the overcurrent device is actuated by the entire current generated other than the current in the shunt field. The over‐ current device shall not open the shunt field.
    3. 65 Volts or Less. Generators operating at 65 volts or less and driven by individual motors shall be considered as protec‐ ted by the overcurrent device protecting the motor if these devices will operate when the generators are delivering not more than 150 percent of their full-load rated current.
    4. Balancer Sets. Two-wire, dc generators used in conjunc‐ tion with balancer sets to obtain neutral points for 3-wire systems shall be equipped with overcurrent devices that discon‐ nect the 3-wire system in case of excessive unbalancing of voltages or currents.
    5. Three-Wire, Direct-Current Generators. Three-wire, dc generators, whether compound or shunt wound, shall be equipped with overcurrent devices, one in each armature lead, and connected so as to be actuated by the entire current from the armature. Such overcurrent devices shall consist either of a double-pole, double-coil circuit breaker or of a 4-pole circuit breaker connected in the main and equalizer leads and tripped by two overcurrent devices, one in each armature lead. Such protective devices shall be interlocked so that no one pole can be opened without simultaneously disconnecting both leads of the armature from the system.
    Exception to (A) through (E): Where deemed by the authority having jurisdiction that a generator is vital to the operation of an electrical system and the generator should operate to failure to prevent a greaterhazard to persons, the overload sensing device(s) shall be permitted to be connected to an annunciator or alarm supervised by authorized person‐ nel instead of interrupting the generator circuit.
  3. Ampacity of Conductors.
    1. General. The ampacity of the conductors from the gener‐ ator output terminals to the first distribution device(s) contain‐ ing overcurrent protection shall not be less than 115 percent of the nameplate current rating of the generator. It shall be permitted to size the neutral conductors in accordance with220.61. Conductors that must carry ground-fault currents shall not be smaller than required by 250.30(A). Neutral conductors of dc generators that must carry ground-fault currents shall not be smaller than the minimum required size of the largest conductor.Exception: Where the design and operation of the generator prevent overloading, the ampacity of the conductors shall not be less than 100 percent of the nameplate current rating of the generator.imageN
    2. Overcurrent Protection Provided. Where the generator set is equipped with a listed overcurrent protective device or a combination of a current transformer and overcurrent relay, conductors shall be permitted to be tapped from the load side of the protected terminals in accordance with 240.21(B).
    Tapped conductors shall not be permitted for portable generators rated 15 kW or less where field wiring connection terminals are not accessible.
  4. Protection of Live Parts. Live parts of generators oper‐ ated at more than 50 volts ac or 60 volts dc to ground shall not be exposed to accidental contact where accessible to unquali‐ fied persons.
  5. Guards for Attendants. Where necessary for the safety of attendants, the requirements of 430.233 shall apply.
  6. Bushings. Where field-installed wiring passes through an opening in an enclosure, a conduit box, or a barrier, a bush‐ ing shall be used to protect the conductors from the edges of an opening having sharp edges. The bushing shall have smooth, well-rounded surfaces where it may be in contact with the conductors. If used where oils, grease, or other contami‐ nants may be present, the bushing shall be made of a material not deleteriously affected.
  7. Generator Terminal Housings. Generator terminal housings shall comply with 430.12. Where a horsepower rating is required to determine the required minimum size of the generator terminal housing, the full-load current of the genera‐ tor shall be compared with comparable motors in Table

430.247 through Table 430.250. The higher horsepower rating of Table 430.247 and Table 430.250 shall be used whenever the generator selection is between two ratings.

Exception: This section shall not apply to generators rated over 600 volts.

445.18 Disconnecting Means and Shutdown of Prime Mover.



  1. Disconnecting Means. Generators other than cord-and-plug-connected portable shall have one or more disconnecting means. Each disconnecting means shall simultaneously open all associated ungrounded conductors. Each disconnecting means shall be lockable in the open position in accordance with 110.25.
  2. Shutdown of Prime Mover. Generators shall have provi‐ sions to shut down the prime mover. The means of shutdown shall comply with all of the following:
    1. Be equipped with provisions to disable all prime mover start control circuits to render the prime mover incapable of starting
    2. Initiate a shutdown mechanism that requires a mechani‐ cal reset
    The provisions to shut down the prime mover shall be permitted to satisfy the requirements of 445.18(A) where it is capable of being locked in the open position in accordance with 110.25.Generators with greater than 15 kW rating shall be provided with an additional requirement to shut down the prime mover. This additional shutdown means shall be located outside the equipment room or generator enclosure and shall also meet the requirements of 445.18(B)(1) and (B)(2).
  3. Generators Installed in Parallel. Where a generator is installed in parallel with other generators, the provisions of 445.18(A) shall be capable of isolating the generator output terminals from the paralleling equipment. The disconnecting means shall not be required to be located at the generator.

445.20 Ground-Fault Circuit-Interrupter Protection for Recep‐ tacles on 15-kW or Smaller Portable Generators. Receptacle outlets that are a part of a 15-kW or smaller portable generator shall have listed ground-fault circuit-interrupter protection (GFCI) for personnel integral to the generator or receptacle as indicated in either (A) or (B):



  1. Unbonded (Floating Neutral) Generators. Unbonded generators with both 125-volt and 125/250-volt receptacle outlets shall have listed GFCI protection for personnel integral to the generator or receptacle on all 125-volt, 15- and 20-ampere receptacle outlets.Exception: GFCI protection shall not be required where the 125-volt receptacle outlets(s) is interlocked such that it is not available for use when any 125/250-volt receptacle(s) is in use.imageN
  2. Bonded Neutral Generators. Bonded generators shall be provided with GFCI protection on all 125-volt, 15- and 20-ampere receptacle outlets.

Informational Note: Refer to 590.6(A)(3) for GFCI require‐ ments for 15-kW or smaller portable generators used for tempo‐ rary electric power and lighting.

Exception to (A) and (B): If the generator was manufactured or rema‐ nufactured prior to January 1, 2015, listed cord sets or devices incorpo‐ rating listed GFCI protection for personnel identified for portable use shall be permitted.