Generator Output Conductor Length

[infinity]

Is there any length limit of generator output conductors between the generator connection box and the OCPD?

 

[ron]

You will not find a length requirement in 445.12.
240.21 says that the OCPD shall be located at the point where the conductors receive their supply (except several cases).
I usually use 10' maximum

 

[infinity]

I'm looking at an installation where the generator switchboard has about 60-70' of conductors between it and the generator.

 

[ron]

I'm looking at an installation where the generator switchboard has about 60-70' of conductors between it and the generator.

In those cases, the generator controller may have a protective relay type listing (UL 6200), which would allow you to protect the conductor from the generator controller (larger kohler and cummins). I've also provided a 50/51 (overcurrent/instantaneous) protective relay or 87 (differential) protective relay for the conductors so they have protection for their long trip from the alternator to their termination onto the breaker.
60-70' is too far, but as I mentioned it is the intent that I use for that opinion.

 

[zbang]

To be clear, there is no OCPD of any kind at the generator itself? (How big a generator?)

 

[infinity]

To be clear, there is no OCPD of any kind at the generator itself? (How big a generator?)

Correct. Just an enclosure with bus where the conductors connect.

 

[acrwc10]

445.13(A) and the exception allow for no overcurrent device at the generator.

 

[ron]

445.13(A) and the exception allow for no overcurrent device at the generator.

For the exception to work, there has to be protection built into the generator controls in some fashion. AHJs that I have run into require those to be listed as protection of some type, like UL 6200 (or even 508 which is pretty generic)

 

[infinity]

Besides an OCPD what could be built in, some type of electronic shutdown?

 

[ron]

Besides an OCPD what could be built in, some type of electronic shutdown?

http://kohlerpower.com/common/pdfs/whitepaper/BreakerFreeGenerators_WP%20Power%20Systems%20Topic%20129.pdf

 

[infinity]

445.13(A) and the exception allow for no overcurrent device at the generator.

All that says is that the conductors need to be sized at 115% of the generator rating or 100% if they meet the exception. Not sure how that is tells us how long those conductors are permitted to be.

445.13 Ampacity of Conductors.
445.13(A) General.
The ampacity of the conductors from the generator output 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 250.30(A). 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.

 

[don_resqcapt19]

If the generator and the conductors are outside, maybe 240.21(B)(5) will work.

 

[infinity]

If the generator and the conductors are outside, maybe 240.21(B)(5) will work.

Both are inside in a mechanical room.

 

[don_resqcapt19]

Both are inside in a mechanical room.

Then it would be my opinion that you have to comply with one of the other feeder tap rules in 240.21(B).

 

[acrwc10]

Then it would be my opinion that you have to comply with one of the other feeder tap rules in 240.21(B).

is it a feeder tap?

 

[acrwc10]

actually I am going to agree with Don, it is a feeder and that rule would apply
"Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device. (CMP-10)

 

[ron]

Then it would be my opinion that you have to comply with one of the other feeder tap rules in 240.21(B).

I use the feeder tap rules, but in reality, it is a Feeder but not a Feeder Tap.

 

[don_resqcapt19]

I use the feeder tap rules, but in reality, it is a Feeder but not a Feeder Tap.

It really is a feeder tap as the conductors are not protected at their ampacity at the point of supply, but does not exactly meet the definition of a tap conductor because there is no OCPD on the supply side of the conductors.

 

[jap]

I would consider any conductor attached to the output of a transformer or generator (prior to any means of overcurrent) a tap.

But that's just me.

JAP>