Storage batteries are used for many different types of electrical equipment throughout the National Electrical Code (NEC). The phrase “storage batteries” occurs in 13 locations in the NEC index. In addition, Article 480 is devoted to the installation requirements for storage batteries.


Solar photovoltaic systems use storage batteries as alternative-power sources at night and where sunlight illumination is not strong enough to generate power. Emergency and standby systems require storage batteries to start the generators that supply power during normal power shutdown. Uninterruptible power supply (UPS) systems, covered by 700.12(C) and 701.12(C), use alternating current (AC) converted to direct current (DC) in large battery banks in battery rooms and then converted back to AC as a backup for critical-power applications. Unit equipment, as covered in 700.12(F) and 701.12(G), requires storage batteries for emergency lighting and exit signs.


With the increased use of DC systems in the 2014 NEC, Article 480 has undergone major changes. Many of these changes were initiated by the Institute of Electrical and Electronic Engineers (IEEE) Battery Group. The NEC Correlating Committee also required the deletion of any battery-room installation requirements from Article 240 of the 2012 NFPA 70E, Standard for Electrical Safety in the Workplace. Many of the battery-room installation requirements from the 2012 edition of NFPA 70E were subsequently inserted into Article 480 in the 2014 NEC.


One of the most important changes occurred in 480.1. An informational note was inserted, containing seven different references to IEEE documents concerning stationary batteries, including references on spill containment, thermal management, design, installation and maintenance information.


There are seven new definitions in 480.2. A battery “cell” is the basic electrochemical unit, characterized by an anode and a cathode, used to receive, store and deliver electrical energy. An “intercell connector” is an electrically conductive bar or cable used to connect adjacent cells, and an “intertier connector” is an electrical conductor used to connect two cells on different tiers of the same rack or different shelves of the same rack of batteries.


The “nominal voltage for a battery or a cell” is the value assigned to a cell or battery of a given voltage class for the purpose of convenient designation. The operating voltage of the cell or battery may vary above or below this value. The nominal voltage of the cell or battery is necessary to indicate the most common cell voltage, which is 2 volts (V) per cell for lead-acid systems, 1.2V per cell for alkali systems, and 3.6 to 3.8V per cell for lithium-ion systems. The nominal voltages may still vary based on the different battery chemistries. As new battery types are developed, there may be changes to the nominal voltage values.


Section 480.3(A) covers battery and cell terminations. Where dissimilar metals may be connected at the battery posts and other interconnection points, an antioxidant material must be used for the battery connections. In 480.3(B), the ampacity of field-­assembled intercell and intertier conductors and connections must be large enough so the temperature rise under maximum load conditions—and at maximum ambient temperature—does not exceed the safe operating temperature of the conductor insulation or of the conductor support material. A new informational note indicates that conductors sized large enough to prevent a voltage from exceeding 3 percent of the maximum anticipated load, with the maximum voltage drop to the farthest point of connection to not exceed 5 percent, may be too high. Therefore, it is inappropriate for all battery applications, based on the 2003 edition of IEEE 1375, Guide for the Protection of Stationary Battery Systems. These values are used as recommended AC branch circuit and feeder voltage drop values. In other words, check the battery manufacturer’s recommendations.


Remote actuation of DC disconnecting means, as well as marking requirements, has been added in 480.6. Ready access of battery terminals in racks and trays is now required in 480.8(C). Working space for battery racks has been added to 480.9(C), so there will be 1 inch between any cell container and a wall of a structure on the side not requiring access for maintenance. Illumination must be provided for any working space containing battery systems based on text in 480.9(G) and shall not be controlled by automatic means only.


Electrical contractors, electricians and designers must thoroughly understand the new requirements in Article 480 before working on any new battery room installations.