445.13 and generator deration

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mikehughes8

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Generators operating at alttitude require deration IAW with manufacturers specs. For sake of argument let's say deration is 10% for every thousand feet. In my case I am being asked to provide spot-generation at 5000' altitiude. So a load that requires 200KW must be sourced with a 400KW generator. If I follow 445.13 I will be required to run parallel runs of 1250mcm to a 1200A breaker (Assuming direct burial 90c 4c cable). But all I really need is a 600A Panel and parallel runs of 350mcm. It seems ridiculous to have to follow this rule in the situation described. It seems a complete waste in equipment and cabling cost. Any thoughts on this?
 
mikehughes8 said:
Generators operating at alttitude require deration IAW with manufacturers specs. For sake of argument let's say deration is 10% for every thousand feet. In my case I am being asked to provide spot-generation at 5000' altitiude. So a load that requires 200KW must be sourced with a 400KW generator. If I follow 445.13 I will be required to run parallel runs of 1250mcm to a 1200A breaker (Assuming direct burial 90c 4c cable). But all I really need is a 600A Panel and parallel runs of 350mcm. It seems ridiculous to have to follow this rule in the situation described. It seems a complete waste in equipment and cabling cost. Any thoughts on this?
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I do not understand how derating for a generator dictates the size of your conductors. I was under the assumption you sized conductors for the load and/or to the OCPD.

I read 445.13 and see where it references the
nameplate current rating of the generator
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but it does not seem clear why this is a requirement. What does altitude have to do with current flow anyway? I can see the generator not putting out as much because of aspiration issues at altitude...............?
 
Mvillines said:
10% for every 1,000 ft @ 5,000 ft = 50%. 1.5 X 200 = 300 kva
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No

A 200KW derated 50% operates as a 100KW generator

Similarly, A 400KW generator derated 50% operates as a 200KW generator

200(.5) = 100
300(.5) = 150
400(.5) = 200 this is what i need

But to be code compliant I need a conductor with an ampacity of 1111.6A x 1.15 or 1278Amps

My load dictates that I need 555A. But becuase of this rule I have to upzize everything.
I don't think I can connect my 1250 cable into a 600A disco.
 
Do a google and you will see there is no need to up size the generator just the prime mover in this case the engine.

Manufactures normally setup their generators to run at at 500 ft If you intend to run a generator at higher altitudes you should let your dealer know this before you purchase a generator
 
Mvillines said:
Do a google and you will see there is no need to up size the generator just the prime mover in this case the engine.

Manufactures normally setup their generators to run at at 500 ft If you intend to run a generator at higher altitudes you should let your dealer know this before you purchase a generator
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Right. Combustion is affected at higher altitudes. The electrical insulating and thermal properties of air are also affected. But the point remains that the whole system gets derated. I need my prime mover to generate electricity. 10% deration is a stretch. It usually falls at 3% per 1000'. But here in Afghanistan I have generators operating at 8000'+.

I just don't understand the need to have to size conductors based on the source instead of the load. We don't do that for transformers why do it for generators. Rate your protection properly and there shouldn't be any problems.
If anyone has an explanation for this requirement I would like to be enlightened.
 
mikehughes8 said:
Generators operating at alttitude require deration IAW with manufacturers specs. For sake of argument let's say deration is 10% for every thousand feet. In my case I am being asked to provide spot-generation at 5000' altitiude. So a load that requires 200KW must be sourced with a 400KW generator. If I follow 445.13 I will be required to run parallel runs of 1250mcm to a 1200A breaker (Assuming direct burial 90c 4c cable). But all I really need is a 600A Panel and parallel runs of 350mcm. It seems ridiculous to have to follow this rule in the situation described. It seems a complete waste in equipment and cabling cost. Any thoughts on this?
Click to expand...

In this case if your 400kw was derated to 200kw due to the altitude it would stand to reason you could also derate the OC devise. Your best option would have the mfg. build the set for this application.
 
If you are installing a 400 and sizing the wire for the 400, then you have not derated

anything. Like others have stated, the prime mover would have to be the peice derated

not the generator. I've never run into this situation.
 
I?m not familiar with high altitude adjustment but here is an attachment for breaker current and voltage adjustments. Current multiplier is .99 and voltage multiplier is .95, above 8,500 the multipliers are .96 and .80 respectively. I think this could be negligible. Breakers are thermo devices and the difference in current and voltage adjustment is minimal with altitude, conductor adjustment is probably even less?.just my onion. But keep searching there could be something significant to this.

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