Generator Question

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tom baker

tom baker

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In NEC section 445.13
"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."

What is considered a distribution device?
Take a 120/208 3 PH generator, that has an 175A main breaker as part of the generator. Is this main breaker considered a distrubution device or is the panelboard that it feeds via the ATS?
 
tom baker said:
In NEC section 445.13
"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."

What is considered a distribution device?
Take a 120/208 3 PH generator, that has an 175A main breaker as part of the generator. Is this main breaker considered a distribution device or is the panelboard that it feeds via the ATS?
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Tom I have always considered the first breaker, be it on the generator or not, to be the first distribution device.

I have not seen a modern generator arrive without a factory breaker so 445.13 is usually a moot point.

However I have seen many older generator installations that the first breaker was mounted on a wall close to the generator, in those cases IMO 445.13 would apply.

JMHO on this one, I don't think it is crystal clear.
 
There are'nt usually any terminals on the genset other than the breaker. I size my conductors from geset to ats at 115% of nameplate or by the size of the breaker, whichever is greater.
 
iwire said:
Tom I have always considered the first breaker, be it on the generator or not, to be the first distribution device.

I have not seen a modern generator arrive without a factory breaker so 445.13 is usually a moot point.

However I have seen many older generator installations that the first breaker was mounted on a wall close to the generator, in those cases IMO 445.13 would apply.

JMHO on this one, I don't think it is crystal clear.
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This is also the way I interpret it. So far no inspectors have given me trouble on it.
 
If you size the conductors with 115% to the first OCPD do you also need to apply that same demand to the first OCPD or is it just the conductors?
 
like Bob said, that 115% is only to the generator breaker. If you are sizing your genset conductors that large that's nice, but I prefer to use that money for the beach or Atlantic City.
 
445.13 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.

Can you name a generator that will run until a mechanical failure results?
 
nakulak said:
like Bob said, that 115% is only to the generator breaker. If you are sizing your genset conductors that large that's nice, but I prefer to use that money for the beach or Atlantic City.
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I realize motor leads have a greater ampacity, thus making them them smaller (those leads are typically 10% smaller than what your are going to run from genset to TS.), but I would have to disagree that the 115% is from the stator to the line side of the genset breaker. IMO, the EC has nothing to do with factory installed stator leads, so why would the NEC be adressing or attempting to govern the issue.
 
360Youth said:
so why would the NEC be adressing or attempting to govern the issue.
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It wasn't always a requirement to have a breaker installed on the gen set.In that case they wanted 115%.
 
It still isn't a requirement to have a breaker on the generator. I have seen several installations where the first OC device is in paralleling gear in the next room, or an insulated case breaker in an enclosure against the wall. These are cases where the 115% rule would come into play.
 
360Youth said:
but I would have to disagree that the 115% is from the stator to the line side of the genset breaker.
Click to expand...

The section does not say genset.

It says from the 'generator to the first distribution device'.

A factory installed breaker is not the 'generator'.

As a few of us have mentioned not all generators are shipped with factory installed breakers.:smile:
 
chris kennedy said:
445.13 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.

Can you name a generator that will run until a mechanical failure results?
Click to expand...

Most generators have one or more mechancial safeties disabled or bypassed rather than repaired.
 
iwire said:
The section does not say genset.

It says from the 'generator to the first distribution device'.

A factory installed breaker is not the 'generator'.

As a few of us have mentioned not all generators are shipped with factory installed breakers.:smile:
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Semantics...semantics. :) But I do see how it can read that way.
 
360Youth said:
Semantics...semantics. :) But I do see how it can read that way.
Click to expand...

It's not semantics, it is what it is. :smile:

The word used is generator not over current device, they chose the word generator for a particular reason.

Had they meant from the breaker they would have said so, IMO.
 
The conductors from the generators altenator usually terminate on the line side of a breaker. Size the conductors as you would a typical feeder.
If the breaker is located remote from the unit you will need to size the conductors at 115%.
I have seen countless installations where the breaker is located in a unit substation several hundred feet away,
Typically a 2 meg unit, 13.8v, 100amps, no breaker on the generator,
one set of 1/0 connected directly to the alternator
 
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