Code Change Summary: New code section. Specific labeling is required for temporary portable generator connections.

A new code section now requires specific labeling near the power inlet for temporary portable generator connections using a power inlet type connection. When connecting a temporary generator to an existing power inlet, it is important to know how the power inlet and associated transfer equipment is wired.

If the existing power inlet is wired to the transfer switch in a way that neutral return current from the generator will return back to the normal premises electrical system grounded conductor, then only a generator wired as a nonseparately system should be used.

If the existing power inlet is wired to the transfer switch in a way that neutral return current from the generator will return back to the generator, then only a generator wired as a separately system should be used.

If a generator configured as a nonseparately derived system is wired to a power inlet wired only for a separately derived system, then a phase to ground fault condition may not cause the overcurrent device for the faulted circuit to trip.

As well, if a generator configured as a separately derived system is wired to a power inlet wired only for a nonseparately derived system, then neutral return current and ground-fault current will have multiple parallel return paths which can diminish the full amount of current returning back to the generator thus affecting the tripping of an overcurrent device.

Below is a preview of the NEC^®.  See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on the “free access” tab and select the applicable year of NFPA 70 (National Electrical code).