i've got 120' of 350/350/4/4 AL wire from transformer to a 400 amp service entrance meter/panel (Siemens MM0404L1400RLM). From there, the 200 amp feeder breaker is going to feed via 2 1/2" conduit to the future house.

That run is 235' to a temporary power panel to be used during construction ( Siemens PW0816B1200TC).

Is 4/0,4/0,2/0,#4 good? Or am I not allowed to down-size the neutral?

  • What will the major electrical loads be? – Harper - Reinstate Monica Jul 20 '18 at 16:35
  • I think the OP is asking about a new service to a 2nd home with a 200 amp panel. With an 83% derate since it is a service for the hots 300 and the Voltage drop will be 2.81%. the neutral can be derated 70% or 250Kim with a voltage drop of 2.81% I think the original OP calculations did not consider the distance. – Ed Beal Jul 20 '18 at 17:33
  • And he should not derate for distance if his actual expected loads do not warrant a derate. However regardless, the wire must meet the code minimum for the breaker – Harper - Reinstate Monica Jul 20 '18 at 19:21
  • What's the HVAC load in the house, what does it have for hot water/dryer/range (electric or gas), and how many square feet is it? – ThreePhaseEel Jul 21 '18 at 3:25

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