The NEC covers storage batteries in two main articles: Article 480 and Article 706. Article 480 applies to all stationary installations of storage batteries, regardless of their chemistry, voltage, or capacity. Article 706 applies to energy storage systems (ESS), which are defined as systems capable of storing energy from one or more sources and delivering that energy to one or more loads. ESS include storage batteries as well as other technologies, such as flywheels, capacitors, and superconducting magnetic energy storage.
Article 480 - Storage Batteries
Article 480 provides general requirements for the installation of storage batteries, such as location, ventilation, accessibility, protection, marking, and maintenance. Some of the key provisions of Article 480 are summarized below:
Storage batteries shall be located in dedicated rooms or enclosures that are separated from other electrical equipment by fire-resistant construction or adequate distance. The rooms or enclosures shall be well ventilated to prevent the accumulation of explosive gases or vapors. The ventilation system shall be designed and operated in accordance with NFPA 70E, Standard for Electrical Safety in the Workplace.
Storage batteries shall be accessible for inspection, maintenance, testing, and replacement. The working space around the batteries shall comply with the requirements of Article 110.26. The battery terminals shall be protected from accidental contact by covers or barriers. The battery containers shall be securely fastened to prevent movement or displacement.
Storage batteries shall be protected from overcurrent, overvoltage, undervoltage, overtemperature, and ground faults by appropriate devices and methods. The overcurrent protection devices shall be sized and located in accordance with Article 240. The overvoltage and undervoltage protection devices shall be selected and installed in accordance with the manufacturer's instructions. The overtemperature protection devices shall be designed to disconnect the battery from the circuit or reduce the charging current when the temperature exceeds a predetermined limit. The ground fault detection system shall be capable of indicating a ground fault on any ungrounded conductor of the battery circuit.
Storage batteries shall be marked with their nominal voltage, ampere-hour capacity, polarity, date of manufacture, and manufacturer's name or trademark. The battery rooms or enclosures shall be marked with warning signs that indicate the presence of energized electrical equipment, electrolyte hazards, and ventilation requirements. The battery circuits shall be identified at all points of connection by color coding, marking tape, tagging, or other means.
Storage batteries shall be maintained in accordance with the manufacturer's recommendations and industry standards. The maintenance activities shall include periodic inspection, testing, cleaning, watering, equalizing, and replacing of defective cells or batteries. The maintenance personnel shall follow the safety precautions specified in NFPA 70E and wear appropriate personal protective equipment.
Article 706 - Energy Storage Systems
Article 706 provides specific requirements for the installation of ESS, which are intended to supplement or modify the general requirements of Article 480 and other applicable articles of the NEC. Article 706 covers ESS that are connected to premises wiring systems or electric power production sources. Some of the key provisions of Article 706 are summarized below:
ESS shall be classified by their technology type (such as electrochemical, mechanical, or electrical), method of operation (such as standalone or interactive), and location (such as indoor or outdoor). The classification of ESS shall determine the applicable requirements for installation, protection, disconnecting means, interconnection, control, monitoring, signage, and labeling.
ESS shall be listed and labeled by a qualified testing laboratory for their intended use and application. The listing and labeling of ESS shall indicate their ratings, characteristics, performance, and safety features. The ESS shall be installed and used in accordance with the manufacturer's instructions and the listing and labeling information.
ESS shall be protected from overcurrent, overvoltage, undervoltage, overtemperature, ground faults, and other abnormal conditions by appropriate devices and methods. The protection devices and methods shall be coordinated with the ESS technology type, method of operation, and location. The protection devices and methods shall also be compatible with the other electrical equipment and systems connected to the ESS.
ESS shall be provided with disconnecting means that are capable of isolating the ESS from all sources of electrical energy. The disconnecting means shall be readily accessible, lockable, and marked to indicate their function and position. The disconnecting means shall also comply with the requirements of Article 690, Article 691, or Article 705, depending on the type of electric power production source connected to the ESS.
ESS shall be interconnected with premises wiring systems or electric power production sources in accordance with the applicable requirements of Article 690, Article 691, or Article 705. The interconnection of ESS shall ensure the proper operation and coordination of the ESS and the other electrical equipment and systems. The interconnection of ESS shall also prevent backfeeding, islanding, or unintentional energization of de-energized circuits.
ESS shall be controlled and monitored by a dedicated energy management system (EMS) or an integrated system that incorporates the functions of an EMS. The EMS shall be capable of regulating the charge and discharge of the ESS, optimizing the performance and efficiency of the ESS, and communicating with the other electrical equipment and systems connected to the ESS. The EMS shall also provide alarms, indicators, and displays for the status and condition of the ESS.
ESS shall be marked with warning signs that indicate the presence of energized electrical equipment, fire hazards, explosion hazards, chemical hazards, and other potential hazards associated with the ESS technology type. The warning signs shall also provide instructions for emergency response and shutdown procedures in case of an incident involving the ESS.
Conclusion
Storage batteries are an essential component of many electrical applications that require reliable and efficient energy storage. However, storage batteries also pose various risks that need to be addressed by proper installation and maintenance practices. The NEC provides comprehensive and updated requirements for the safe installation of storage batteries and ESS in Articles 480 and 706. By following these requirements, electrical professionals can ensure the safety and performance of storage batteries and ESS.
References
NFPA 70E, Standard for Electrical Safety in the Workplace
NFPA 70, National Electrical Code
Article 480 - Storage Batteries
Article 706 - Energy Storage Systems
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