3 phase 400 amp residential service

[SpotOn]

Can anyone point me in the right direction on sizing and installing service cables on a 3-phase 400 amp service. I'm used to installing service laterals which the poco pulls, but this one will be an over head. Should I run 2 sets of 250 kcmil AU in a 4" PVC conduit? I assume I cant use 310.15(b)(6) since the service is three phase. what are your thoughts?

 

[Dennis Alwon]

You cannot use (B)(6) as you stated. You can run 2 runs and then you don't have to derate. If you run one conduit then you must deal with 310.15(B)(2)(a) 2008 NEC-- 310.15(B)(2)(a) 2011

 

[Dennis Alwon]

250 al. will work with 2 runs in one conduit if the calculated load is not greater than 184 amps and you use 90C wire-- assuming the neutral does not count as a CCC. I didn't check fill

 

[Little Bill]

Can anyone point me in the right direction on sizing and installing service cables on a 3-phase 400 amp service. I'm used to installing service laterals which the poco pulls, but this one will be an over head. Should I run 2 sets of 250 kcmil AU in a 4" PVC conduit? I assume I cant use 310.15(b)(6) since the service is three phase. what are your thoughts?

My thoughts are:
Why a 3? for residential?
What equipment in the house uses 3??
Or are all the loads single ? and 3? just happens to be what the service is?

I agree with the Dennis on sizing, but wonder a little about the neutral not being CCC.

 

[SpotOn]

250 al. will work with 2 runs in one conduit if the calculated load is not greater than 184 amps and you use 90C wire-- assuming the neutral does not count as a CCC. I didn't check fill

Would that be 368 amps per leg since they are paralleled?
Do installers ever run 2 separate conduits? for example (2) 2 1/2" conduits with one set of 250 Al in each (rated at 205 amps) to eliminate the need for 310.15(b)(2)(a)

 

[SpotOn]

My thoughts are:
Why a 3? for residential?
What equipment in the house uses 3??
Or are all the loads single ? and 3? just happens to be what the service is?

I agree with the Dennis on sizing, but wonder a little about the neutral not being CCC.

I should Clarify....... This is a three family house with electric heat. The Property is in a commercial area where 3phase 120/208 is available.
There is also a warehouse on the property that is being fed from this service. All of the units including the warehouse will be fed with single phase.

 

[Little Bill]

I should Clarify....... This is a three family house with electric heat. The Property is in a commercial area where 3phase 120/208 is available.
There is also a warehouse on the property that is being fed from this service. All of the units including the warehouse will be fed with single phase.

Ok, makes sense now. I kind a figured that was the case.
I would also say that the neutral would be counted as a CCC in this case.

 

[hmspe]

Do installers ever run 2 separate conduits?

It is quite common. I frequently specify two conduits, each with four #350MCM alluminum for a 400A, 120/208V service. That's with temperature derate for 122 degF (Arizona).

 

[kwired]

Are you supplying a single 400 amp overcurrent device or three (or more) smaller devices?

If supplying multiple devices these conductors only need to be sized according to art 220 load calculations. If load calculations only come to say 360 amps then you only need a 360 amp conductor or parallel equivelant.