Generator output feeder sizing

[bdarnell]

Article 445.13 states:

The ampacity of the conductors from the generator terminals to the first distribution device(s) containing overcurrent protection shall not be less than 115 percent of the nameplate current rating of the generator. It shall be permitted to size the neutral conductors in accordance with 220.22. Conductors that must carry ground-fault currents shall not be smaller than required by 250.24(B). Neutral conductors of dc generators that must carry ground-fault currents shall not be smaller than the minimum required size of the largest conductor.

Exception: Where the design and operation of the generator prevent overloading, the ampacity of the conductors shall not be less than 100 percent of the nameplate current rating of the generator.

My question is, if a generator has an output breaker at the generator, does the exception apply here ? I think it does, but I'd like the Forum opinion.

Thanks

 

[steve66]

I think I have asked this before also. I think the consensus was that the "first distribution overcurrent device" was the breaker mounted on the generator. So the 115% wire campacity would be installed by the manufacturer. Any wire you install would only have to comply with any other NEC rules.

And they say that "The NEC is not a manufacturing standard".

Steve

 

[DGrant041]

Bob-

That's the way we apply it, too. If the manufacturer supplies a breaker mounted on the generator then that is their way of "limiting" the output to <115%. Size the conductors to the breaker, 75C, blah, blah, blah . . .

Good luck,

Dale

 

[ryan_618]

I've kicked this one around a lot myself. I believe it applies to the internal wiring of the generator.

 

[jwelectric]

Would that breaker on the Generator be required to be sutiable as service equipment and if so would the conductots leaving the breaker then be feeders?

 

[Nick]

The manufacturer is not always the one that supplies the wiring. In multiple generator applications the wiring to the first overcurrent device is installed in the field by us (electricians) because the OC device is generally inside paralleling switchgear some distance away. These installations are always engineered and generally the engineer of record sizes the cable from the generator terminals to the OC device to the size of the OC protection. This is almost always larger than the 115% requires but I believe the 115% would be code compliant.

 

[frenchelectrican]

Neutral conductors of dc generators that must carry ground-fault currents shall not be smaller than the minimum required size of the largest conductor.

ok this question is for DC or AC generator ??


i just want to make sure i am reading this right


genrally most generator manufacter can have breaker mounted on the generator at < 115 % of FLC

merci , marc

 

[bdarnell]

Thanks for the responses. That's pretty much the way we were reading it also.

 

[DGrant041]

ok this question is for DC or AC generator ??


i just want to make sure i am reading this right


genrally most generator manufacter can have breaker mounted on the generator at < 115 % of FLC

The ampacity of the conductors from the generator terminals to the first distribution device(s) containing overcurrent protection shall not be less than 115 percent of the nameplate current rating of the generator. It shall be permitted to size the neutral conductors in accordance with 220.61. Conductors that must carry ground-fault currents shall not be smaller than required by 250.24(C). Neutral conductors of dc generators that must carry ground-fault currents shall not be smaller than the minimum required size of the largest conductor.
Exception: Where the design and operation of the generator prevent overloading, the ampacity of the conductors shall not be less than 100 percent of the nameplate current rating of the generator.

Marc,

I work for a generator packager. We take a manufacturer's genset, put it in a container/skid, and add the support equipment before it goes to a customer's building. This has been a 100% custom business and standards are not well know throughout the electrical industry.

Our policy is if the genset has a breaker mounted on it, we can wire it to 100%. Of course, if the breaker is on the genset, our customer will usually put their wires there, not us. If the first OCPD is at our switchgear, we wire it at 115%. We have to wire the neutral conductors the same as the ungrounded conductors since we don't know the application. If you work for the consumer, they may not need that size.

Hope this helps.

-Dale

PS Do you know where I could find IEC codes and wire ampacities? Is there a link to these codes on the internet?

 

[don_resqcapt19]

My take on this rule is that it lets me run an unlimited length of wire between the generator terminals and the OCPD as long as the wire is sized at or above 115% of nameplate output.
Don