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NEC 700.3 – Temporary Source of Power for Maintenance or Repair of the Alternate Source of Power

The 2017 National Electric Code (NEC) introduced provisions that impact emergency power system design.  The first provision impacts start signal requirements between the power transfer equipment (such as a transfer switch) and the emergency generator set controller; the provision requires fail safe operation of the generator set if the start signal wiring is compromised. 

The second provision address temporary power source connection requirements during the maintenance or repair of the emergency generator set.  This course will take a deep dive into these two requirements including review of exceptions, NEC amendments, and solutions.

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.

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.  The new code requirement ensures that during these times, the building occupants are still provided with a working emergency system.



Below is a preview of the NEC.  See the actual NEC text at
NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2017 NEC edition of NFPA 70.

2017 Code Language:

N (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.

It shall be permissible to utilize manual switching to switch from the permanent source of power to the portable or temporary alternate source of power and to utilize the switching means for connection of a load bank.


In summary, Provision 700.3(F) of the 2017 National Electrical Code requires a permanent point of connection for a mobile generator. That connection point needs to be installed and a mobile generator needs to be deployed for automatic operation, when the generator (defined as an emergency system or legally required standby system) is offline for maintenance and repairs. Additionally, a remote annunciator or alarm panel is required to give an audible and visual annunciation that the permanent emergency source is disconnected from the emergency source.

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