A common code violation written up by the electrical inspector involves emergency light circuits not being supplied from the normal area lighting circuits.

In past editions of the NEC^®, the general rule for wiring emergency lighting unit equipment was to supply the emergency unit equipment from the same branch circuit that supplies the normal lighting in the area. This ensures that the emergency lights will illuminate not only when all power to the building is lost, but even if only an individual circuit fails that serves the normal area lighting.

There was an exception to the above general rule:

Exception: In a separate and uninterrupted area supplied by at least three normal lighting circuits, (that are not part of a multiwire branch circuit), a separate branch circuit for emergency unit equipment is permitted as long as it originates from the same panelboard as that of the normal lighting circuits and is provided with a lock-on feature.

During the 2020 NEC^® development, it was recognized that sometimes there may not be three or more normal lighting circuits, especially with the improved technology such as LED normal area lighting that uses much less electricity.

During the 2020 NEC^® development process, the exception was simplified and turned into positive text to require the branch circuit supplying emergency unit equipment must be either one of the following:

• The same branch circuit as that serving the normal lighting in the area and connected ahead of any local switches
• A branch circuit that is separate from the normal area lighting circuit, provided with a lock-on feature, that originates from the same panelboard as the normal lighting circuits.

Below is a preview of the NEC^® (NFPA 70). See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the edition of the NEC^® being enforced.

NEC 700.12(I)(2) Installation of Unit Equipment. Unit equipment shall be installed in accordance with the following:

(1) The batteries shall be of suitable rating and capacity to supply and maintain the total lamp load associated with the unit in accordance with the following:

1. For a period of at least 1-1/2 hours without the voltage falling below 87-1/2 percent of normal battery voltage.
2. The unit equipment shall supply and maintain not less than 60 percent of the initial emergency illumination for a period of at least 1-1/2 hours.

(2) Unit equipment shall be permanently fixed (i.e., not portable) in place 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.

(3) The branch circuit feeding the unit equipment shall be one of the following:

1. The same branch circuit as that serving the normal lighting in the area and connected ahead of any local switches
2. Where the normal lighting circuit is served by one or more branch circuits, a separate branch circuit, provided with a lock-on feature, that originates from the same panelboard as the normal lighting circuits. The branch circuit disconnecting means for this branch circuit shall be provided with a lock-on feature.

(4) The branch circuit that feeds unit equipment shall be clearly identified at the distribution panel.

(5) Emergency luminaires that obtain power from a unit equipment and are not part of the unit equipment shall be wired to the unit equipment as required by 700.10 and by one of the wiring methods of Chapter 3.

(6) Remote heads providing lighting for the exterior of an exit door shall be permitted to be supplied by the unit equipment serving the area immediately inside the exit door.