445.13

[ryan_618]

445.13 tells me that, unless an exception is met, I must have conductors are rated at 115% of the nameplate rating of the generator. So, if I have a 60KVA generator, running at single phase 240, I would have an amperage of 250 amps. I then 115% of that 250 and come up with 287.5 amps. That tells me that I would need a conductor not smaller than 350 Kcmil. My question is, what if the generator has an internal 200 amp breaker in it? Do I still have to size the conductor for 287 amps? If so....why?

 

[bphgravity]

Re: 445.13

I think the exception covers you. But even in that case, you would still need 250 kcmil.

I wonder why they sized the breaker smaller than the maximum rating?

 

[steve66]

Re: 445.13

I think the answer is no. If the generator has an internal breaker, the 115% rule only applies to the wires feeding this breaker, which would be factory wiring.

Steve

 

[ryan_618]

Re: 445.13

Well, in this particular installation, they are adding a generator as an optional standby for an existing building. They have an existing 200 amp service with an outside breaker that goes to a 200 amp MLO panel inside. They have added a transfer switch so that the generator can pick up the entire building. So, the existing feeder circuit going to the panel is 3/0, whish is good for 200 amps. The problem is that the language in 445.13 leads me to think that the feeder circiut would have to be replaced with conductors good for 115% of the the 287 amps, or best case scenrio, 250 amps. Either way, they would have to be removed and replaced, since 445.13 requires these conductors to be sized from the nameplate to the first distribution device containing overcurrent protection.

So, what is a distribution device? The panel? The transfer switch? The OCPD in the generator?

 

[jcross]

Re: 445.13

Doesn't 445.13 refer to the conductors between the generator terminals and the first overcurrent device? I would think that the first overcurrent device would be the one in the generator and you could size your conductors from that point @ 200 Amps. Sound right???

 

[steve66]

Re: 445.13

Ryan:

I'll admit I didn't focus too much on the term "distribution device". But it seems clear to me that the 115% only applies to conductors with no overcurrent protection on their supply side. In effect, they are required to be slightly larger due to their lack of overcurrent protection.

I don't think the exception would apply. A breaker would allow the generator to be overloaded for a short time. I think the exception applies more to voltage or current regulators that would instantly limit the output.

Steve

 

[rbalex]

Re: 445.13

The onboard OCPD is the "the first distribution device containing overcurrent protection" with respect to the "generator terminals."