Main electric service line too long?

BobReeves · Nov 11, 2005

I ran conduit from the meter to the house and shop (both 150 ft runs) for two reasons. If ever need to replace the wire I can do it without trenching and conduit doesn't need to be buried as deep. For the price of 2 inch PVC it was an easy decision. The funny part is I have direct burial cable in the conduit.

LarryRB · Nov 11, 2005

( I guess I am baffled. Why would you use conduit? Around here, code is apparently to use wires suitable for direct burial. I have seen even the high-voltage runs done this way (no conduit, just the wires in a trench). Why are you all putting down conduit? /forums/images/graemlins/confused.gif )
For one, it is our code that schedule 40 be used. Second, we have a gazillion rocks and boulders that constantly work their way upwards from underground, and that is the reason for piping...

rswyan · Nov 12, 2005

( The funny part is I have direct burial cable in the conduit. )
I'm doing the same thing - 2" schedule 40 PVC with 4/0 4/0 2/0 URD.

For me the big advantage will be not having to bury it so deep - I have to cross 1 culvert and a pair of french drain lines, all of which are buried fairly close to the surface.

GaryBDavis · Nov 13, 2005

Okay, I need to make sure I understand the 4/0 for the lines and 2/0 for the neutral. I’ve heard that the NEC allows you to use a neutral that is two sizes smaller than the lines. I’m guessing this applies only to main feeds for 240V single phase.

I’ve always run the same size neutral as it stands to reason that you have as much current going through the line as you do through the neutral - for 120V circuits that is. I’m guessing that the reason they let you run a smaller neutral is because the loads are supposed to be fairly balanced load between the two 120V lines. Since they are 180 degrees out of phase, their currents cancel out on the neutral line. The 220V circuits don’t even use the neutral.

Is this right or is there another reason?

BobReeves · Nov 13, 2005

I agree the nutral doesn't need to be any larger than the feed lines. The nutral only sees(carries) one phase at any given time.

rswyan · Nov 25, 2005

Gary,

I can't comment on your questions regarding the reduced neutral - it sounds good to me - but then I'm not an electrician and have limited knowledge in the area .... where's Inspector507 when you need him .... ? /forums/images/graemlins/grin.gif

I'm just operating off what I was told would work for my particular situation.

midlf · Nov 26, 2005

correct. some balance between the two legs is assumed thus allowing for a reduced neutral. If you have a situation where you know this not true then a larger neutral is needed. Very unlikely in a residential type situation.