1200 amp service

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memyselfandI

memyselfandI

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Hampton Roads, Virginia
Here is one for everyone. I have an electrical contractor getting ready to install a 1200 A sub fed panel in an industrial facility. He said that he was going to install 3 sets of 500 MCM CU with a 3/0 CU ground with each set. As I looked at 310.16 and looked at the table, I noticed that three sets of 500 will only come to 1140 A according to the 75 degree column. When I mentioned this to him he said that he was using the 90 degree column for the circuit and that because it was a higher amperage rating that the overage was okay for a 1200 A breaker and that if he based it on the 75 deg column the next higher breaker rating is 1200 A anyway. I asked him if his connections were rated for 90 deg and he said no they are rated for 75 deg. I was under the assumption that he can use the 90 deg column for his wires, but if the terminations are only rated for 75 deg then the value of the conductors are only good for the value in the 75 deg column. To me the conductors for this circuit are not adequate for the OCP. It seems that he is sizing the breaker to the conductors and not the conductors to the breaker. Now we all know that there is no way that the circuit will pull 100% of the load, 110.14 C (b) if I interpret it right, is specific on the temperature limitation on connections when dealing with circuits of 100A or more. My question is this, is this acceptable practice to size the conductors in this manner or are there other provisions in the code that allow this?
 
Not 100% sure, I need to dig out my code book (which is still packed up in boxes) but I think you can go up in breaker size if it's over 800 amp. again not 100% sure. I'm sure others will chime in. I think you should have posted this in the engineering area.
 
khixxx said:
Not 100% sure, I need to dig out my code book (which is still packed up in boxes) but I think you can go up in breaker size if it's over 800 amp. again not 100% sure. I'm sure others will chime in. I think you should have posted this in the engineering area.
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You can't use the next standard size over 800A. SEee 240.4(C).
 
He is right about sizing the wire for the terminals. I think some money could be saved installing 4 sets 250MCM. At least the per foot price for the copper is only about 66%.
 
75 degree connections=75 degree conductor rating. As Ryan pointed out going up to the next standard size cannot be used. The conductors would need to be rated for a full 1200 amps or a smaller OCPD needs to be used.

4 sets of 250 Kcmil conductors won't work either.

4*255 amps = 1020 amps

You would need 3 sets of 600 Kcmil or 4 sets of 350 Kcmil to use a 1200 amp OCPD.
 
Its funny. I was reviewing plans for a 1,000A service today, and they specified (4) 250 KCMIL. I looked it up, saw that it complied and continued my plan review.

So...when I see the part of this thread that talked about (4) 250's, I told myself "I know that works, I don't even need to look it up". I completelty forgot that it was a 1,000A service on the plans today, and a 1,200A in this thread! :(
 
ryan_618 said:
Its funny. I was reviewing plans for a 1,000A service today, and they specified (4) 250 KCMIL. I looked it up, saw that it complied and continued my plan review.

So...when I see the part of this thread that talked about (4) 250's, I told myself "I know that works, I don't even need to look it up". I completelty forgot that it was a 1,000A service on the plans today, and a 1,200A in this thread! :(
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1000 amps seems like an odd size for a service. We generally see 400, 600, 800, 1200, 1600, 2000 etc.
 
infinity said:
4 sets of 250 Kcmil conductors won't work either.

4*255 amps = 1020 amps

You would need 3 sets of 600 Kcmil or 4 sets of 350 Kcmil to use a 1200 amp OCPD.
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aghh, must have been late when I posted that. the copper price for 4 300MCM is still cheaper, but not a lot.
 
bradleyelectric said:
aghh, must have been late when I posted that. the copper price for 4 300MCM is still cheaper, but not a lot.
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4 sets of 300's might be cheaper but it's still not big enough.:smile:
 
Is there any provisions for connected load. If there is something showing the connected load, can they still use the conductors and feed it with a 1200 amp breaker. It is a feeder that will feed a panel, which in turn will feed a chiller system for a/c. I still say that they are undersized on their conductors, but I am wondering if there is some kind of reference to a connected load and sizing the conductors
 
memyselfandI said:
Is there any provisions for connected load. If there is something showing the connected load, can they still use the conductors and feed it with a 1200 amp breaker.
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No, they are undersized per the NEC.

If they where feeding just a chiller than maybe, but they are feeding a panel, the breaker must be the same or less than the ampacity of the conductors.
 
Thanks for the input people. I have went through different locations trying to find the reason as to why these people did it this way and it all pointed me back to 240.4 C. One good thing about this site is that when you post a question, you have a million minds thinking of the answer. Pretty amazing isn't it.
 
No one is as smart as all of us together

No one is as smart as all of us together

I also believe in accuracy though volume when in doubt empty the magazine.
 
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