11.2 Generators, Storage Batteries and Energy Storage Systems

Article 445 — Generators

445.10 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. Generators installed in hazardous (classified) locations as described in Articles 500 through 503, or in other locations that are attributable to hazardous (classified) conditions of operation and maintenance, shall comply with the applicable provisions of those articles.

445.11 Marking. Each generator shall be provided with a nameplate giving the manufacturer's name, rated frequency, number of phases if AC, rating in kilowatts or kilovolt-amperes, normal volts and amperes corresponding to the rating, rated revolutions per minute, insulation system class and rated ambient temperature or rated temperature rise, time rating, power factor, subtransient and transient impedances, and, for stationary generators, whether the neutral is bonded to the generator frame. Generators arranged to operate in parallel shall be marked accordingly. A generator with a factory-installed overcurrent device shall be marked with the maximum load current for which the device is set.

445.12 Overcurrent Protection. Constant-voltage generators, except AC generator exciters, shall be protected from overload by inherent design, circuit breakers, fuses, protective relays, or other identified overcurrent protective means suitable for the conditions of use.

445.13(A) Ampacity of Conductors. The ampacity of the conductors from the generator terminals to the first distribution device containing 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 with 220.61. Conductors that must carry ground-fault currents shall not be smaller than required by 250.30.

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.

445.13(B) 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).

445.18 Disconnecting Means and Shutdown of Prime Mover.

• (A) Disconnecting Means. Generators, other than cord-and-plug-connected portable generators, 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.
• (B) Shutdown of Prime Mover. Generators shall have provisions 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; and (2) initiate a shutdown mechanism that requires a mechanical 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.
• (C) Generators with Greater Than 15 kW Rating. For generators with greater than 15 kW rating, a remote emergency stop switch shall be provided to shut down the prime mover. The remote emergency stop switch shall be located outside the equipment room or generator enclosure and shall also meet the requirements of 445.18(B)(1).
• (D) Emergency Shutdown of Prime Mover in Other Than One- and Two-Family Dwellings. Where a generator is installed in a parallel configuration with other generators or other power production sources, in other than one- and two-family dwellings, the disconnecting means shall be provided with a means to disable all prime mover start control circuits.

445.19 Generators Supplying Multiple Loads. A single generator supplying more than one load, or multiple generators operating in parallel, shall be permitted to supply the following: (1) an emergency system; (2) a legally required standby system; (3) an optional standby system; (4) a parallel power production system; or (5) an interconnected electric power production source. Where the generator or generators supply more than one class of load, other articles of the Code shall apply.

445.20 Ground-Fault Circuit-Interrupter Protection for Receptacles on 15-Kilowatt or Smaller Portable Generators. All 125-volt, single-phase, 15- and 20-ampere receptacle outlets that are a part of a 15-kilowatt or smaller portable generator shall have ground-fault circuit-interrupter protection for personnel integral to the generator or receptacle, in accordance with the conditions of the section. Listed cord sets or devices incorporating listed GFCI protection identified for portable use shall be permitted.

445.11 requires stationary generators to be marked as to whether the neutral is bonded to the generator frame. That marking answers the separately-derived-system question from section 9.6: a generator whose neutral is bonded at the frame and whose transfer switch does not switch the neutral will create a parallel neutral path unless the bond is removed.

Interconnection and Transfer Equipment

702.5 Capacity and Rating (Optional Standby Systems). Optional standby system equipment shall be suitable for the maximum available fault current at its terminals. The calculated load shall be in accordance with Article 220 or by another approved method.

702.6 Transfer Equipment. Transfer equipment shall be required for all standby systems subject to the provisions of Article 702 and for which an electric utility supply is either the normal or standby source. Transfer equipment shall be suitable for the intended use, designed and installed so as to prevent the inadvertent interconnection of all sources of supply in any operation of the transfer equipment, and shall be listed and marked for emergency, legally required, or optional standby use as applicable.

702.7 Signals and 702.12 Outdoor Generator Sets complete the general requirements. 702.12(A) provides that where an outdoor housed generator set is equipped with a readily accessible disconnecting means located within sight of the building or structure supplied, an additional disconnecting means shall not be required where ungrounded conductors serve or pass through the building or structure.

Article 480 — Stationary Standby Batteries

480.4 Battery and Cell Terminations. (A) Corrosion prevention — antioxidant material shall be permitted to be used on battery terminals. (B) Intercell and intertier conductors and connections shall be sized to carry the maximum anticipated current.

480.5 Wiring and Equipment Supplied from Batteries. Wiring and equipment supplied from storage batteries shall be subject to the requirements of the Code applying to wiring and equipment operating at the same voltage.

480.6 Overcurrent Protection for Prime Movers. Overcurrent protection shall not be required for conductors from a battery with a voltage of 60 volts DC or less if the battery provides power for starting, ignition, or control of prime movers.

480.7 Disconnecting Means.

• (A) Disconnecting Means. A disconnecting means shall be provided for all ungrounded conductors derived from a stationary battery system over 60 volts DC. A disconnecting means shall be readily accessible and located within sight of the battery system.
• (B) Remote Actuation. Where a disconnecting means located remote from the battery system is provided, a means shall be provided at the battery system to remotely actuate the disconnecting means.
• (C) Notification. The disconnecting means shall be legibly marked in the field with nominal battery voltage, available fault current derived from the stationary battery system, an arc-flash label applied in accordance with acceptable industry practice, and the date the calculation was performed.
• (D) Emergency Shutdown. In one- and two-family dwellings, a disconnecting means or its remote control for a stationary battery system exceeding 60 volts shall be located at a readily accessible location outside the building for emergency shutdown.

480.9 Battery Support Systems. (A) Racks shall be substantial and treated to be resistant to deteriorating action by the electrolyte. (B) Trays shall be treated to be resistant to deteriorating action by the electrolyte.

480.10 Battery Locations.

• (A) Ventilation. Provisions appropriate to the battery technology shall be made for sufficient diffusion and ventilation of gases from the battery to prevent the accumulation of an explosive mixture.
• (B) Live Parts. Guarding of live parts shall comply with 110.27.
• (C) Working Space. Working space about the battery systems shall comply with 110.26. Working clearance shall be measured from the edge of the battery rack.
• (D) Top Terminal Batteries. Where top terminal batteries are installed on tiered racks or on stacked modules, working space shall be provided in accordance with the battery manufacturer's instructions.
• (E) Egress. A personnel door intended for entrance to and egress from rooms designated as a battery room shall open in the direction of egress and shall be equipped with listed panic hardware.

480.12 Battery Interconnections. Flexible cables, as identified in Article 400, in sizes 2/0 AWG and larger shall be permitted within the battery enclosure from battery terminals to a nearby junction box where they shall be connected to an approved wiring method.

Article 706 — Energy Storage Systems

706.1 Scope. Article 706 applies to all permanently installed energy storage systems (ESS) operating at over 50 volts AC or 60 volts DC that may be stand-alone or interactive with other electric power production sources.

706.5 Listing. Energy storage systems shall be listed. Where an energy storage system is composed of a combination of listed components, the completed installation shall be approved.

706.7 Maintenance. Energy storage systems shall be maintained in proper and safe operating condition. Documentation of the maintenance shall be maintained.

706.15 Disconnecting Means. A disconnecting means shall be provided for all ungrounded conductors derived from an ESS. A disconnecting means shall be readily accessible and located within sight of the ESS. Where the disconnecting means is remote from the ESS, a directory showing the location of each disconnect shall be installed at the ESS location, and remote actuation shall be provided.

706.15(C) Notification. The disconnecting means shall be legibly marked in the field with the nominal ESS voltage, available fault current, an arc-flash label, and the date the calculation was performed.

706.15(E) Disconnection of Series Battery Circuits. Battery circuits subject to field servicing, where more than 240 volts DC are present, shall have provisions to disconnect the series-connected strings into segments not exceeding 240 volts DC for maintenance by qualified persons.

706.20 General (Installation). ESS shall be installed in accordance with the manufacturer's instructions and the listing.

706.21 Directory. A permanent plaque or directory shall be installed at each service equipment location or at an approved readily visible location, denoting the location of each power source disconnecting means for the building or structure.

706.30 Circuit Sizing and Current. Requirements for calculating maximum current and sizing conductors and overcurrent protection for ESS circuits.

Cold-Climate Considerations

These are engineering and manufacturer-listing matters, not separate Code rules, but they determine whether an Alaska installation works.

Lithium-ion charging below freezing. Lithium-ion chemistries, including lithium iron phosphate, generally cannot accept charge current at cell temperatures below 0 degrees C (32 degrees F) without plating metallic lithium on the anode, which permanently reduces capacity and can create an internal short. Manufacturers address this with battery management systems that block charging below a temperature threshold, and often with integral heaters. The Code hook is 706.5 (the ESS must be listed) and 110.3(B) (installed per the instructions), including any minimum ambient temperature stated in the listing. Discharging at low temperature is generally permitted at reduced capacity; charging is the limited operation.

Lead-acid capacity loss. Flooded and valve-regulated lead-acid batteries lose usable capacity as temperature drops — roughly a quarter of rated capacity at minus 18 degrees C. A discharged lead-acid battery can also freeze, because its electrolyte approaches the freezing point of water as specific gravity falls. Sizing must account for the design low temperature.

Ventilation still applies. 480.10(A) requires ventilation appropriate to the battery technology to prevent accumulation of an explosive mixture. Enclosing a vented lead-acid bank in a sealed insulated box to keep it warm creates a hydrogen accumulation hazard. Heat the space, do not seal the battery.

Generator installation. Diesel gensets in Alaska require block heaters, battery warmers, and fuel treated or heated against gelling. None of that is NEC content, but the electrical consequence is real: the block heater and battery charger are loads that must be included in the service calculation, and a block heater receptacle outdoors requires GFCI protection under 210.8.