600MCM to 400A breaker

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DAWGS

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Virginia
Installing a new 400A panel that is being fed from a 600A buss plug. We ran 4" conduit and pulled 600MCM. Engineer we are working for supplied panel with 400A main breaker insted of main lug. When we went to term breaker we noticed it had dual lugs and would only except up to 500MCM per hole. Engineer called square D tech support and they said breaker only needs 500MCM because you are only supposed to load it to 80% therefore 500MCM is suficient. I have never heard of this. I understand for services the exceptions but this is not the case. 500MCM is only good for 380A at 75deg witch is what their lugs are rated. Engineer didnt argue with him just said OK. Our solution was to use ILSCO terminal crimps on the ends of our wires. Has anybody ran into this problem before?
 
Yep. We upsized for voltage drop. It wouldn't fit into the Square D breaker. They didn't offer any solutions, so we used wire reducers.

Enjoy the fun
 
BLUEDEVIL said:
industry standard for circuit breakers 800A or less is 80% rated so for your 400A breaker you only need 500kcmil
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That is correct.

ILSCO is a way to go, but you can also replace the Sq'D terminals with a bolted bus connector and use two-hole compression terminals on the cable end.

We run into this many times on branch circuits off of panels where the conductors are oversized due to voltage drop. Reducing lugs worked perfectly fine. The only problem is that they are not readily available and if you don't plan for this minor detail it can cut into your profit because of the wait.
 
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We had to overnight the ilsco terminals. Just talked to my foreman and panel is up and hot. For some reason I only thought that the 240.4 rule applyed to services only.
 
DAWGS said:
they said breaker only needs 500MCM because you are only supposed to load it to 80% therefore 500MCM is suficient.
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No this is not correct, you may load a 400 amp breaker up to 400 amps non-continuous and / or 80% continuously.

If the calculated load is under the usable ampacity of the conductor 240.4(B) allows us to use a 400 amp breaker with the 500 kcmil CU.

Look on the front of the breaker, normaly there will be listed other lug kits you can get to accept different combination of breakers.

On the jobs I work on 600 Kcmil CU is a very common conductor for a 400 amp feeder.
 
weressl said:
It is not the NEC it is the UL rating of the breakers.
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It's actually both and both allow loading to 100% non-continuous.

In the NEC you can find it in 215.2(A) for feeders, 210.19(A) for branch circuits and 230.42 for services.

Unless you happen to have a 100% rated over current device but they are pretty rare.
 
iwire said:
In the NEC you can find it in 215.2(A) for feeders, 210.19(A) for branch circuits and 230.42 for services.
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Correction, 215.3 for feeders, 210.20(A) for branch circuits, and I am still looking for services.
 
DAWGS said:
Installing a new 400A panel that is being fed from a 600A buss plug. We ran 4" conduit and pulled 600MCM. Engineer we are working for supplied panel with 400A main breaker insted of main lug. When we went to term breaker we noticed it had dual lugs and would only except up to 500MCM per hole. Engineer called square D tech support and they said breaker only needs 500MCM because you are only supposed to load it to 80% therefore 500MCM is suficient. I have never heard of this. I understand for services the exceptions but this is not the case. 500MCM is only good for 380A at 75deg witch is what their lugs are rated. Engineer didnt argue with him just said OK. Our solution was to use ILSCO terminal crimps on the ends of our wires. Has anybody ran into this problem before?
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The Square D 400A breaker was supplied with dual lugs for use with parallel conductors (i.e. 2-#3/0). Did you ask if there were optional lugs available, like their #AL600LI7 that lets a LC breaker handle 1-600kcmil instead?
 
Sounds like someone screwed up and ordered the CB without the proper lugs. This happens from time to time. 600 kcmil for a 400 amp feeder is fairly standard.
 
Engineer ordered breaker and panel. I always size 600MCM for 400A or paralell 3/0. Run is only 25' from buss plug to panel. Square D rep basicly called the engineer an idiot because we used 600MCM like it was some huge overkill for the breaker. there is no calculated load for the panel because the load will change as they add equipment. This is at a foundery and they are always changing and relocating equipment.
 
DAWGS,
Don do you mean 500 KCMIL?
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No. If you are over 25' then you can't use the tap rule and the conductors between the bus duct and the 400 amp panel would have to have an ampacity of 600 amps.
Don
 
DAWGS,
Don, Its not tap rule, we have the 600A plug fused down to 400A.
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In that case, as long as the calculated load is 380 amps or less, you can use 500s and be in compliance with the code.
Don
 
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