Another shop electrical supply ?

[Troy Lee]

I am planning out my run of 100 amp service to my out building wired from my house and have run into a question.

I am running nearly 200 feet of 2/0 copper which will be for the two hot legs. My question concerns the neutral leg. Does this have to be 2/0 also. That was my plan but have been told by someone who is supposed to know that I can run a lesser wire size for this neutral. With the price of the materials being so high this would save considerably if possible.

Maybe running all three the same errs on the side of safety which is preferred.

[Randy Denby]

Neutrals can usually be a size smaller as long as the load is fairly balanced. This for the power supply only...not individual runs. Dont put more than 2 circuits per neutral as you run the risk of burning up the neutral.....As a matter of fact, we installed new underground wire for my buddies new shop tonight. The cable came from the electrical supply wholesaler in a twisted set of two 4 oughts and one 2 ought (neutral).

[Vernon Taylor]

Have you considered having a seperate service for the shop? I have a stand alone shop about 70 foot from the house which has it:s own service. I guess it would depend on your site but this worked for me. Given the distance you have to run it might be cheaper to do. Mine is 200 amp. This results in a seperate billing but for me the advantages are that I know exactly what power I am using in the shop and the service does not impact the capacity of the main house.May or may not work for you ,but certainly worth looking at.

[Rod Sheridan]

Hi, there are two items involved;

1) Have voltage drop calculations been performed on the feeder length?

2) Your local electrical inspector will be able to give you permission to use a smaller neutral, if allowed by local codes. He will also be able to help you with any other technical aspects of the required permit.


Regards, Rod.

[David G Baker]

Suggestion, run the fourth leg (ground) from your main power panel, it will make life much easier. If you don't you will not be able to have any metal connection to the building that the main power panel is located in. No water lines, no cable lines, no gas lines, no phone lines, etc or you could end up with a ground loop.
I always use the same size wire for all 3 or 4 legs. It is not cheaper but it simplifies things for me.

[Troy Lee]

I will return my thoughts to running the same size for the neutral. Voltage drop calculations call for 1/0 which is what I will probably end up running. I was not planning on running other services but will consider the ground line being run as maybe I will want those services sooner than later.

[Josiah Bartlett]

I just got done replacing a burnt out neutral to my detached garage. It has a 50 amp service, the neutral looked to be #8 or so and the mains were #4. I had a new roof put on and the roofers were plugging their compressors (3 of them) into my 20 amp garage outlets (I have 3 separate outlet circuits). Between those, the refrigerator, the lights, and probably something else, my neutral burnt out without blowing a breaker. I found out about it when I plugged in a circular saw and all the lights got really bright and burnt out.

Believe me, it is a real pain to replace a neutral after the fact. I would go with the same size as the main conductors.

I should have just had the roofers use my shop air.

[Rick Christopherson]

I just got done replacing a burnt out neutral to my detached garage. It has a 50 amp service, the neutral looked to be #8 or so and the mains were #4. Josiah, If your neutral got burned out, then it may be possible that you have something else going on. #8 wire can handle over 50 amps, and even though it would get warm or even hot, it would not be to the point of damaging the wire. If anything, it would have just damaged the insulation (yes, this can lead to other damage).

You didn't mention anything about having 240 volts in your garage, and this has me a bit concerned. If both legs of your subpanel are feeding off the same phase in the main load center, then you are in fact pushing 100 amps through your neutral! This will definitely damage the conductor. If you have a volt meter, you should measure the voltage across the main legs in your subpanel. If they are only 120 volts apart, then you need to shift your breakers up or down by one position in the main load center.

Under normal conditions, the current through the neutral is only the differential current of the two hot legs. If you had equal loads placed on both phases, then there would be zero neutral current. This is the reason why under some applications the neutral can be smaller. However, if both legs are using the same phase, then the neutral current is no longer differential, but additive.

[Rick Christopherson]

I will return my thoughts to running the same size for the neutral. Voltage drop calculations call for 1/0 which is what I will probably end up running. I was not planning on running other services but will consider the ground line being run as maybe I will want those services sooner than later.Even though you will be carrying your ground from the main load center, don't forget that you still need to drive a ground rod at the separate building as well. This new ground rod is treated as just an extension of the original.

I am not an expert when it comes to figuring the size of the feeders, but I believe you are well within the limits with the 1/0 that you already have, and voltage drop is hardly an issue when you get into the larger conductors. Before shelling out a large amount of money on the feeders, I think you should get a couple of opinions on this. Come to think of it, your best source for this would be a call to your local inspector.

[Brandon Shew]

If you're running a 2/0 then your neutral could be a 4/0. If you're running a 1/0 then your neutral could be a 2/0. I'm running a 60 AMP panel w/ two 6/0 hot wires and one 8/0 neutral. My detached shop is not grounded back to my main building. I have a separate 8' ground rod driven into the ground, but I don't have or plan to have any other services out there. I am within range of a cordless phone and I don't need water or cable TV. Most natural gas is plastic tubing these days so no worries about ground loop if that's the case.

[Von Bickley]

If you're running a 2/0 then your neutral could be a 4/0. If you're running a 1/0 then your neutral could be a 2/0. I'm running a 60 AMP panel w/ two 6/0 hot wires and one 8/0 neutral. My detached shop is not grounded back to my main building. I have a separate 8' ground rod driven into the ground, but I don't have or plan to have any other services out there. I am within range of a cordless phone and I don't need water or cable TV. Most natural gas is plastic tubing these days so no worries about ground loop if that's the case.

I don't like to bust anybody's ballon, but you have your numbers wrong.

2/0 or 2 AWG can be ran with a 1/0 or 1 AWG neutral.

What you have for your supply line is NOT 6/0, but a #6 with a #8 neutral.

There's a lot of confusion about wire size. 2/0 or 2 AWG is not the same as #2.