The NEC^® is an installation code, not a performance code, this concept has been made clear throughout the NEC^®. However, when life safety is involved, sometimes the rules are bent a little.

Section 700.3 requires testing and routine maintenance of the emergency system which goes far beyond the initial installation. Section 700.12(F) requires batteries in emergency lighting and exit signs to maintain power for 90 minutes so that the building occupants can get out safely. Section 700.16 requires emergency lighting to be arranged so that the failure of one lamp doesn’t leave in total darkness, any area requiring emergency illumination.

Section 700.3(F) requires a way to ensure emergency systems remain operational when the main emergency source (such as an emergency generator) is taken offline for service or maintenance.

Sometimes an emergency generator needs more than just an oil change. Often, major repairs might be needed which warrant the need to disable the generator for an extended period of time. This code requirement ensures that during these times, the building occupants are still provided with a working emergency system and emergency illumination where required.

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 700.3(F) Temporary Source of Power for Maintenance or Repair of the Alternate Source of Power. If the emergency system relies on a single alternate source of power, which will be disabled for maintenance or repair, the emergency system shall include permanent switching means to connect a portable or temporary alternate source of power, which shall be available for the duration of the maintenance or repair. The permanent switching means to connect a portable or temporary alternate source of power shall comply with the following:

(1) Connection to the portable or temporary alternate source of power shall not require modification of the permanent system wiring.

(2) Transfer of power between the normal power source and the emergency power source shall be in accordance with 700.12.

(3) The connection point for the portable or temporary alternate source shall be marked with the phase rotation and system bonding requirements.

(4) Mechanical or electrical interlocking shall prevent inadvertent interconnection of power sources.

(5) The switching means shall include a contact point that shall annunciate at a location remote from the generator or at another facility monitoring system to indicate that the permanent emergency source is disconnected from the emergency system.