706- Energy Storage Systems

706.1 – Energy Storage Systems

Change at a Glance:

The scope of Article 706 has been revised to provide clarity and to better express what is covered by the article.

706.1 Scope. (Energy Storage Systems)

This article 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 having a capacity greater than 3.6 MJ (1 kWh) that may be stand-alone or interactive with other electric power production sources. These systems are primarily intended to store and provide energy during normal operating conditions.
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: (See NEC for complete list of standards added and deleted at this informational note)

706.2 – Energy Storage System (ESS)

Change at a Glance:

Revision occurred to the previous definition of an Energy Storage System (ESS) to better define an what an ESS is and is not.

706.2 Definitions. (Energy Storage System)

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 for use at a future time. ESS(s) can include but is not limited to batteries, capacitors, and kinetic energy devices (e.g., flywheels and compressed air). These systems can have ac or dc output for utilization and can include inverters and converters to change stored energy into electrical energy.
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.
Energy Storage System, Self-Contained. Energy storage systems where the components such as cells, batteries, or modules and any necessary controls, ventilation, illumination, fire suppression, or alarm systems are assembled, installed, and packaged into a singular energy storage container or unit.
Informational Note: Self-contained systems will generally be manufactured by a single entity, tested and listed to safety standards relevant to the system, and readily connected on site to the electrical system and in the case of multiple systems to each other.
Energy Storage System, Pre-Engineered of Matched Components. Energy storage systems that are not self-contained systems but instead are pre-engineered and field-assembled using separate components supplied as a system by a singular entity that are matched and intended to be assembled as an energy storage system at the system installation site.
Informational Note: Pre-engineered systems of matched components for field assembly as a system will generally be designed by a single entity and comprised of components that are tested and listed separately or as an assembly.
Energy Storage System, Other. Energy storage systems that are not self-contained or pre-engineered systems of matched components but instead are composed of individual components assembled as a system.
Informational Note: Other systems will generally be comprised of different components combined on site to create an ESS. Those components would generally be tested and listed to safety standards relevant to the application.

706.4 – Nameplates for Energy Storage Systems

Change at a Glance:

New marking requirements (nameplate information) added for energy storage systems. Marking requirement in this revision correlates with the marking requirements found in UL 9540.

706.4 System Classification Requirements. (Energy Storage Systems)

Each ESS shall be classified as one of the types described as follows provided with a nameplate plainly visible after installation and marked with the following:
(1) ESS, self-contained Manufacturer’s name, trademark, or other descriptive marking by which the organization responsible for supplying the ESS can be identified
Informational Note: Some self-contained systems may be listed. (2)ESS, pre-engineered of matched components Rated frequency
(3)ESS, other Number of phases, if ac
(4) Rating (kW or kVA)
(5) Available fault current derived by the ESS at the output terminals
(6) Maximum output and input current of the ESS at the output terminals
(7) Maximum output and input voltage of the ESS at the output terminals
(8) Utility-interactive capability, if applicable

706.7 – Maintenance of Energy Storage Systems (ESS)

Change at a Glance:

New provisions added calling for maintenance of energy storage systems (ESS).

706.7 Maintenance. (Energy Storage Systems)

Energy storage systems shall be maintained in proper and safe operating condition. The required maintenance shall be in accordance with the manufacturer’s requirements and industry standards. A written record of the system maintenance shall be kept and shall include records of repairs and replacements necessary to maintain the system in proper and safe operating condition.
Informational Note: For information related to general electrical equipment maintenance and developing an effective electrical preventive maintenance (EPM) program, see NFPA 70B-2016 Recommended Practice for Electrical Equipment Maintenance or ANSI/NETA ATS-2017, Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems.

706.9 – Maximum Voltage of an ESS

Change at a Glance:

New section added to provide prescriptive requirements for the determination of maximum voltage of an ESS.

706.9 Maximum Voltage. (Energy Storage Systems)

The maximum voltage of an ESS shall be the rated ESS input and output voltage(s) indicated on the ESS nameplate(s) or system listing.

706.30(A)(1) – Nameplate-Rated Circuit Current

Change at a Glance:

Revision occurred to clarify that an ESS may have two nameplates, each respectively indicating input or output circuit rating, or one nameplate showing input and output circuit ratings.

706.20 706.30 Circuit Sizing and Current. (Energy Storage Systems)

(A) Maximum Rated Current for a Specific Circuit. The maximum current for the specific circuit shall be calculated in accordance with 706.20 706.30(A)(1) through (A)(5).
(1) Nameplate-Rated Circuit Current. The nameplate(s)-rated Circuit current shall be the rated current indicated on the ESS nameplate(s) or system listing for pre-engineered or self-contained systems of matched components intended for field assembly as a system. Where the ESS has separate input (charge) and output (discharge) circuits or ratings, these shall be considered individually. Where the same terminals on the ESS are used for charging and discharging, the rated current shall be the greater of the two.