Article 701 Legally Required Standby Systems
The systems covered by this article consist only of those that are permanently installed in their entirety, including the power source.
Informational Note No. 1: For further information, see NFPA 99-2018, Health Care Facilities Code.
Informational Note No. 2: For further information regarding performance of emergency and standby power systems, see NFPA 110-2019, Standard for Emergency and Standby Power Systems.
Informational Note No. 3: For further information, see ANSI/IEEE 446-1995, Recommended Practice for Emergency and Standby Power Systems for Industrial and Commercial Applications.
Legally Required Standby Systems. Those systems required and so classed as legally required standby by municipal, state, federal, or other codes or by any governmental agency having jurisdiction. These systems are intended to automatically supply power to selected loads (other than those classed as emergency systems) in the event of failure of the normal source.
Informational Note: Legally required standby systems are typically installed to serve loads, such as heating and refrigeration systems, communications systems, ventilation and smoke removal systems, sewage disposal, lighting systems, and industrial processes, that, when stopped during any interruption of the normal electrical supply, could create hazards or hamper rescue or fire-fighting operations.
Informational Note: For information on testing and maintenance of emergency power supply systems (EPSSs), see NFPA 110-2019, Standard for Emergency and Standby Power Systems.
Transfer equipment shall be automatic, listed, and marked for emergency system or legally required standby use, and approved by the authority having jurisdiction. Transfer equipment shall be designed and installed to prevent the inadvertent interconnection of normal and alternate sources of supply in any operation of the transfer equipment. Transfer equipment and electric power production systems installed to permit operation in parallel with the normal source shall meet the requirements of Article 705. Meter-mounted transfer switches shall not be permitted for legally required system use.
Informational Note: For signals for generator sets, see NFPA 110-2016, Standard for Emergency and Standby Power Systems.
For systems with multiple emergency sources connected to a paralleling bus, the ground fault sensor shall be permitted at an alternate location.
Informational Note: For signals for generator sets, see NFPA 110-2019, Standard for Emergency and Standby Power Systems.
The warning sign(s) or label(s) shall comply with 110.21(B).
Informational Note: For further information, see ANSI/IEEE 493-2007, Recommended Practice for the Design of Reliable Industrial and Commercial Power Systems.
An automatic battery charging means shall be provided.
Exception: Where approved by the authority having jurisdiction, the use of other than on-site fuels shall be permitted where there is a low probability of a simultaneous failure of both the offsite fuel delivery system and power from the outside electrical utility company.
Where a single fuel cell system serves as the normal supply for the building or group of buildings concerned, it shall not serve as the sole source of power for the legally required standby system.
A dc microgrid system used as a source of power for legally required systems shall be of suitable rating and capacity to supply and maintain the total legally required load for not less than 2 hours of full-demand operation.
Where a dc microgrid system source serves as the normal supply for the building or group of buildings concerned, it shall not serve as the sole source of power for the legally required standby system.
- A rechargeable battery
- A battery charging means
- Provisions for one or more lamps mounted on the equipment and shall be permitted to have terminals for remote lamps
- A relaying device arranged to energize the lamps automatically upon failure of the supply to the unit equipment
The batteries shall be of suitable rating and capacity to supply and maintain the total lamp load associated with the unit for not less than the following:
- For a period of 11/2 hours, without the voltage falling below 871/2 percent of normal voltage.
- The unit equipment shall supply and maintain not less than 60 percent of the initial emergency illumination for a period of at least 11/2 hours.
Unit equipment shall be permanently fixed in place (i.e., not portable) and shall have all wiring to each unit installed in accordance with the requirements of any of the wiring methods in Chapter 3. Flexible cord-and-plug connection shall be permitted, provided that the cord does not exceed 900 mm (3 ft) in length. The branch circuit feeding the unit equipment shall be the same branch circuit as that serving the normal lighting in the area and connected ahead of any local switches. Legally required standby luminaires that obtain power from a unit equipment and are not part of the unit equipment shall be wired to the unit equipment by one of the wiring methods of Chapter 3.
Exception: In a separate and uninterrupted area supplied by a minimum of three normal lighting circuits, a separate branch circuit for unit equipment shall be permitted if it originates from the same panelboard as that of the normal lighting circuits and is provided with a lock-on feature.