Article 706 Energy Storage Systems
Informational Note No. 1: For batteries rated in ampere hours, kWh is equal to the nominal rated voltage times ampere-hour rating divided by 1000.
Informational Note No. 2: There can be a subtle distinction between a battery storing energy and an energy storage system. A battery storing energy is not necessarily an ESS. See Article 480. An ESS can be comprised of batteries storing energy. See Article 706.
Informational Note No. 3: The following standards are frequently referenced for the installation of energy storage systems:
- NFPA 111-2016, Standard on Stored Electrical Energy Emergency and Standby Systems
- NECA 416-2016, Recommended Practice for Installing Energy Storage Systems (ESS)
- UL 810A, Electrochemical Capacitors
- UL 1973, Standard for Batteries for Use in Stationary, Vehicle Auxiliary Power, and Light Electric Rail (LER) Applications
- UL 1989, Standard for Standby Batteries
- UL 9540, Standard for Safety Energy Storage Systems and Equipment
- UL Subject 2436, Spill Containment For Stationary Lead Acid Battery Systems
Diversion Charge Controller. Equipment that regulates the charging process of an ESS by diverting power from energy storage to direct-current or alternating-current loads or to an interconnected utility service.
Energy Storage System (ESS). One or more components assembled together capable of storing energy and providing electrical energy into the premises wiring system or an electric power production and distribution network.
Informational Note No. 1: ESS(s) can include but is not limited to batteries, capacitors, and kinetic energy devices (e.g., flywheels and compressed air). Energy storage systems can include inverters or converters to change voltage levels or to make a change between an ac or a dc system.
Informational Note No. 2: These systems differ from other storage systems such as a UPS system, which is a power supply used to provide alternating current power to a load for some period of time in the event of a power failure.
Flow Battery. An energy storage component similar to a fuel cell that stores its active materials in the form of two electrolytes external to the reactor interface. When in use, the electrolytes are transferred between reactor and storage tanks.
- Manufacturer's name, trademark, or other descriptive marking by which the organization responsible for supplying the ESS can be identified
- Rated frequency
- Number of phases, if ac
- Rating (kW or kVA)
- Available fault current derived by the ESS at the output terminals
- Maximum output and input current of the ESS at the output terminals
- Maximum output and input voltage of the ESS at the output terminals
- Utility-interactive capability, if applicable
Informational Note: For information related to general electrical equipment maintenance and developing an effective electrical preventive maintenance (EPM) program, see NFPA 70B-2019, Recommended Practice for Electrical Equipment Maintenance, or ANSI/NETA ATS-2017, Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems.
- The disconnecting means shall be readily accessible.
- The disconnecting means shall be located within sight of the ESS. Where it is impractical to install the disconnecting means within sight of the ESS, the disconnect shall be installed as close as practicable, and the location of the disconnecting means shall be field marked on or immediately adjacent to the ESS. The marking shall be of sufficient durability to withstand the environment involved and shall not be handwritten.
- The disconnecting means shall be lockable open in accordance with 110.25.
- Nominal ESS ac voltage and maximum ESS dc voltage
- Available fault current derived from the ESS
- An arc-flash label applied in accordance with acceptable industry practice
- Date the calculation was performed
Exception: List items (2), (3), and (4) shall not apply to one- and two-family dwellings.
Informational Note No. 1: Industry practices for equipment labeling are described in NFPA 70E-2018, Standard for Electrical Safety in the Workplace. This standard provides specific criteria for developing arc-flash labels for equipment that provides nominal system voltage, incident energy levels, arc-flash boundaries, minimum required levels of personal protective equipment, and so forth.
ELECTRIC SHOCK HAZARD
TERMINALS ON THE LINE AND LOAD
SIDES MAY BE ENERGIZED IN THE OPEN POSITION
The notification(s) and marking(s) shall comply with 110.21(B).
Informational Note No. 2: Some storage technologies do not require ventilation.
Informational Note No. 3: A source for design of ventilation of battery systems is IEEE 1635-2018/ASHRAE. Guideline 21-2018, Guide for the Ventilation and Thermal Management of Batteries for Stationary Applications.
Informational Note No. 4: Fire protection considerations are addressed in NFPA 1-2018, Fire Code.
Exception: Where the assembly, including the overcurrent protective devices, is listed for operation at 100 percent of its rating, the ampere rating of the overcurrent devices shall be permitted to be not less than the maximum currents calculated in 706.30(B).