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Thread: Wire size for 400 amp service

  1. #1
    Join Date
    May 2007
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    Wire size for 400 amp service

    I need to give a price on a 400 amp, 3 phase 4 wire service, and I don't want to get burned by the derating issue. I was planning on running 4 500mcms in a 4" pvc pipe, the pipe will be about 100' long above a drop ceiling in a retail area. I know by having 4 current carrying conductors I need to derate, but I am not sure how to go about this, any help is appreciated.

  2. #2
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    Are you needing all 400 amps?
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  3. #3
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    Quote Originally Posted by millspgh
    I need to give a price on a 400 amp, 3 phase 4 wire service, and I don't want to get burned by the derating issue. I was planning on running 4 500mcms in a 4" pvc pipe, the pipe will be about 100' long above a drop ceiling in a retail area. I know by having 4 current carrying conductors I need to derate, but I am not sure how to go about this, any help is appreciated.
    It seems way too far for service conductors considered inside the building envelope. If you end up with feeders, will you need to include an equipment grounding conductor in the conduit as well? :-?

  4. #4
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    May 2007
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    service

    I know I will need an equipment ground also. I am sure th store will not need all 400 amps, but the panel will be a 400 amp main breaker panel

  5. #5
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    May 2007
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    service

    Also, this is coming from an outdoor fused disconnect on the outside of the building, which is fed from an outdoor trough that is fed from a 1200 amp switch outside.

  6. #6
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    310.16...

    Quote Originally Posted by millspgh
    I know I will need an equipment ground also. I am sure th store will not need all 400 amps, but the panel will be a 400 amp main breaker panel
    Correct me if I'm wrong but according to Table 310.16 -- 500 CU is only rated at 380 amps at 70 deg.
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  7. #7
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    millspgh, I think you're confusing Feeders and Services. You should read 310.15(B) for whether the neutral will need to be counted as a Current Carrying Conductor.


    Roger
    Last edited by roger; 05-07-07 at 06:54 PM.
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  8. #8
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    Mills, are you designing this or bidding from plans?

  9. #9
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    Quote Originally Posted by 1793
    Correct me if I'm wrong but according to Table 310.16 -- 500 CU is only rated at 380 amps at 70 deg.
    Would 240.4(B) allow him the next standard rating?

  10. #10
    Join Date
    May 2007
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    There are no blue prints, the owner of the shopping plaza asked me to give him a price on putting a 400 amp panel in a location a Family Dollar is moving into, fed from the outside of the building at a 4oo amp fused disconnect switch

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