[Saturday Cowboy]

For a 30a service to an out building you will need 4-10ga wires. H-H-N-G If no more than 6 breakers you will not need a disconnect. You will have to install a ground rod at the out building. You will have to keep all neutrals and grounds separate at the out building. Sorry it will be difficult to post code sections as this is a summary of many articles. Romex cannot be used outside nor underground, so this will have to be UF cable @24" deep or conduit and THWN @ 18".

 

[vsheetz]

I am running wiring to the rear of a barn for small devices, like lights. No large motors. The one way run is about 70 feet.

I thought of using a 20A, 220V circuit breaker, plus common and ground to give 2, 110V circuits. Both hot wires will be 10 AWG. I believe ground can be 12 AWG, but that is not the real question.

How many common wires, also 10 AWG, do I need to run? If you can cite the code portion too, that would be a great help.

Thanks, John

You need two hots, ground, and nuetral. All can be #12 to provide two 20a 120 circuits via a MWBC (multi wire branch circuit). The nuetral is shared by the two circuits.

 

[Saturday Cowboy]

sorry I didn't see that OP wanted 20a @ out building, I only saw the mention of 10ga wire and ASSUMED(shame on me) that he needed 30a.

wire sizes and min breaker size:

14ga=15a
12ga=20a
10ga=30a

Or larger wire can be used, never smaller gauge wire.

 

[john4153]

Thanks for the replies. I should have been more clear on some details, but I don't think they will change the answer.

The building already has its own 200A panel and meter. I chose 10 AWG, because the one-way distance from the panel to the furthest outlet is so far.

I knew I could run the two hots with a single neutral for 2X110V, as I did that for some relatively low current ceiling lamps years ago with a licensed electrician.

What I didn't know was how to calculate the gauge required by code for the neutral, when the hots could potentially be delivering 20 A each. My understanding from the answers is that a single, 10 AWG neutral will still suffice, which makes sense.

Thanks and let me know if that restatement changes the answer.

John

 

[vsheetz]

Oh, so this is simply installing a couple new circuits in an existing building - I took it as getting power to the building.

70' is not far at all. Why not just run #12 Romex. One 12/2 run for each of the two circuits separately, or a 12/3 as a MWBC.

 

[john4153]

I have read so much about mice/voles eating and chewing on modern plastic insulation that I decided to use EMT and pull the wires. This barn is in real country and there are plenty of mice.

John

 

[vsheetz]

I have read so much about mice/voles eating and chewing on modern plastic insulation that I decided to use EMT and pull the wires. This barn is in real country and there are plenty of mice.

John

ok, that makes good sence - or get a couple cats.

Still 70' is not a long run - no need to over-size the wiring..

 

[john4153]

12 AWG is a lot cheaper too! Again, thanks.

John

 

[Missouri Bound]

Are you running a sub-panel or just a couple of circuits?

 

[john4153]

@ Missouri Bound

Just a few circuits along the wall for lights, hand tools a so forth. I would like 20A at 110V capable.

John

 

[bob22]

If an actual barn with livestock, aren't there special sections of the code that require various kinds of wiring, grounding, cable protection, etc... that differ from just using NM in a house or garage?

 

[Jim Port]

If an actual barn with livestock, aren't there special sections of the code that require various kinds of wiring, grounding, cable protection, etc... that differ from just using NM in a house or garage?

Depending on the livestock type, an equilpotential grid would be required. The physical damage criteria might also change due to chewing etc.

 

[HouseHelper]

Thanks for the replies. I should have been more clear on some details, but I don't think they will change the answer.

The building already has its own 200A panel and meter. I chose 10 AWG, because the one-way distance from the panel to the furthest outlet is so far.

I knew I could run the two hots with a single neutral for 2X110V, as I did that for some relatively low current ceiling lamps years ago with a licensed electrician.

What I didn't know was how to calculate the gauge required by code for the neutral, when the hots could potentially be delivering 20 A each. My understanding from the answers is that a single, 10 AWG neutral will still suffice, which makes sense.

Thanks and let me know if that restatement changes the answer.

John

If you run a multi wire branch circuit (MWBC), the neutral is sized the same as the hots since it will only carry the difference in current between the two hots, so never more than an individual hot. A MWBC requires that a double pole breaker or two single pole breakers with a handle tie be used.