Residential Generators

[R Bob]

I have a B&S 20KW Gen Set to wire.
The nameplate current rating is 83.3A@240V.
The generator has a factory installed 100A CB.

445.13(NEC2002) states that the size of the conductors between the terminals of the generator and the first overcurrent device need to be sized @115% of the nameplate current rating (83.3x1.15=95.795A).

The exception to 445.13 states that the conductors can be sized @100% of the nameplate current rating where the design and operation of the generator prevent overloading. [Also read 445.12(A)].
According to the mfr, this generator is inherently protected against overload. In fact, it would seem to me that all generators of this type are inherently protected. The exception seems to apply in this case. Anyone agree/disagree?

However, use of the exception to 445.13 creates a problem if the conductors are sized @100%/83.3A because they will be overfused @ the 100A CB rating. (I understand that the generators UL Listing requires a 100A CB)

In short, it appears that the exception to 445.13 is useless in this case and in most stationary stand-by generator applications.

Any thoughts?

 

[RUWired]

Any thoughts?

Article 445.13 pertain to the conductors from the gen set windings to the first ocpd.This is the breaker on the gen set. Being a 20kw unit the kva rating would be 25 kva, (104.1 amps) thus the 100 amp breaker, but is inherently protected at 80% (83.3 amps). The conductors from the gen set should already be rated 115% of 104 amps.
Rick