OverCurrent Protection For 800 Amp Service

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ill

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I'm not sure if I'm placing this in the proper section.
In New York City:

Say I'm installing an 800 Amp service, I can use two sets of 500 MCM (KCM for the rest of the country) and fuse it at 800 Amps or 400 Amps per set. This is allowed in New York City knowing that a temperature derate places the value of each set at 380 Amps @ 75 degrees Celsius.

Question:
Is this allowed in other areas of the country?
 
ill said:
Question:
Is this allowed in other areas of the country?
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It is everywhere I know of. 240.4(B) of the National Electric Code.

Welcome to the Forum and get well soon!
 
NYC is under an amended version of the 2005 NEC so they should be using kcmil instead of the old MCM.

As Chris stated 240.4(B) allows you to go up to the next standard sized OCPD so for parallel 500's the ampacity is as you stated 380 * 2 = 760 amps. If your connected load is 760 or less you can go up to an 800 amp OCPD. I'm not sure why you mentioned derating since I don't see how it applies here.

Welcome to the forum.:)
 
I missed that. Thanks for the heads up. You know how many times I read that section and missed that part. I'm in there looking for something and fail to observe everything else.

Thanks guys.

The derate is a temperature derate. Well, maybe I described it using the wrong term. Considering that the equipment is rated for 75 degrees Celsius, I wouldn't use the conductor at the THHN rating which 90 degrees Celsius.
 
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ill said:
The derate is a temperature derate. Well, maybe I described it using the wrong term. Considering that the equipment is rated for 75 degrees Celsius, I wouldn't use the conductor at the THHN rating which 90 degrees Celsius.
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Mabey I'm misunderstanding. Your not derating but using the value from T310.16 at 75?C

If you do need to derate use 90?C as per 100.14(C). Heres the last sentence.


Conductors with temperature ratings higher than specified for terminations shall be permitted to be used for ampacity adjustment, correction, or both.
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Chris you're absolutely correct. I'm not doing a derate. I'm simply using the conductor value as it is stated for 75 degrees Celsius, for a 500MCM conductor it would 380 Amps.

No one that I know of in New York City in Local 3 or non-union uses the term kcm, kilo circular mils for 1000 circular mils. I do know that the M is a Roman numeral for 1000. It may have to do with the fact that we just started using the NEC, with the 1999 NEC I believe, and it may take some time to sink in. Remember, until recently, we had our own code. I happen to enjoy the fact that we went National, but I too still use some of the old terms that I have become accustomed to using.

Hey Chris, thanks for the get well card. I'll do my best to get well soon.
 
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