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Thread: Parallel Service Conductors

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    Parallel Service Conductors

    Hey Guys, I'm installing a service for a customer and it's going to be a 120/240 volt 200 amp service with 3/0 wire( 2 hots and one neutral). The customer wants's the underground to be 3 inch schedule 80 so if he ever wants to upgrade he can do so. I am under the impression from the code book that if he wanted to go from 200 to 400 amps I could just pull another 2 hots and a neutral to the service head. so that would be four hots and 2 neutrals in parallel all in the same 3 inch. A friend at work told me I cannot do this according to code but I am having trouble finding the appropriate nec article. Any advice?

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    Quote Originally Posted by patricknola View Post
    Hey Guys, I'm installing a service for a customer and it's going to be a 120/240 volt 200 amp service with 3/0 wire( 2 hots and one neutral). The customer wants's the underground to be 3 inch schedule 80 so if he ever wants to upgrade he can do so. I am under the impression from the code book that if he wanted to go from 200 to 400 amps I could just pull another 2 hots and a neutral to the service head. so that would be four hots and 2 neutrals in parallel all in the same 3 inch. A friend at work told me I cannot do this according to code but I am having trouble finding the appropriate nec article. Any advice?
    I would say you could do that. 3" looks good for nine 3/0 conductors. You need to derate for more than 3 current carrying conductors. 3/0 copper at 75 degree chart is 200amps, so 400 amps derated at 80% is 320amps, which is what you might be going to on a residential service.
    Also depends on the POCO

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    Quote Originally Posted by patricknola View Post
    Hey Guys, I'm installing a service for a customer and it's going to be a 120/240 volt 200 amp service with 3/0 wire( 2 hots and one neutral). The customer wants's the underground to be 3 inch schedule 80 so if he ever wants to upgrade he can do so. I am under the impression from the code book that if he wanted to go from 200 to 400 amps I could just pull another 2 hots and a neutral to the service head. so that would be four hots and 2 neutrals in parallel all in the same 3 inch. A friend at work told me I cannot do this according to code but I am having trouble finding the appropriate nec article. Any advice?
    Yes it would work as you've described. Since you would end with 4 CCC's the derating would be 80%. If you can use a 90° C conductor you can derate from that ampacity. 225*.8*2=360 amps.

    As Gerry stated for certain residential services you only need to have a conductor ampacity of 83% so 332 amps is your minimum parallel conductor size for 400 amps.
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

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    Quote Originally Posted by GerryB View Post
    I would say you could do that. 3" looks good for nine 3/0 conductors. You need to derate for more than 3 current carrying conductors. 3/0 copper at 75 degree chart is 200amps, so 400 amps derated at 80% is 320amps, which is what you might be going to on a residential service.
    Also depends on the POCO
    310.15(B)(3)(a), 310.15(B)(16), Table C9, 310.15(B)(3)

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