Outbuilding wire

waugh621 · Oct 8, 2023

My dad is building a small shop on his proprty and was wanting to run a 220v service to it. The building is roughly 100ft from the source pannel in the house. What gauge wire would we need to run?
Thanks nate

Jim.ME · Oct 8, 2023

(quoted from post at 12:59:55 10/08/23) My dad is building a small shop on his proprty and was wanting to run a 220v service to it. The building is roughly 100ft from the source pannel in the house. What gauge wire would we need to run?
Thanks nate

The size of wire depends not only on distance but also the load it is expected to carry. What does he intend to run for electric equipment in this shop. Lights, motor driven equipment voltage and amps, welder, heat, etc.?

WNYBill · Oct 8, 2023

I agree with Jim, you have to decide on how many amps you need. In our area UF is cheaper than pull wire and conduit. In fact, it is cheaper than regular Romex.

Geo-TH,In · Oct 8, 2023

Go to Menards. Buy either a 100 or 200 amp load center. Menards only sells the wire for each application, nothing between. It's up to you how much money you want to spend. I'm betting after you do the math, you will use aluminum. You will need 4 wire for a sub-panel.
After you price PVC conduit, you will not use it.
My power company buries wires and they don't use conduit.
I would only consider using conduit if I had shape rocks in my dirt, which I don't.

waugh621 · Oct 8, 2023

Mostly simple power tools bit he has always wanted a plasma cutter (dont know why) and a place for me to do whatever welding he needs. I'm not an electrician but i was thinking 59A correct me if i'm wrong this isn't my wheel house

Hemmjo · Oct 8, 2023

Here are some typical values for 100' copper conductor. Assuming less that 3% voltage drop

100 amp #1
75 amp #3
50 amp #6
20 amp #12

Use the calculator to enter your values. You SHOULD run this in PVC conduit to protect the wire. ALSO, if you are going to have 220/240 power. You NEED to run 4 conductors. 2-Hot, 1-neutral and 1-dedicated ground wire. DO NOT use neutral for the ground.
WIre Size Calculator

Jim.ME · Oct 8, 2023

(quoted from post at 13:24:18 10/08/23) Go to Menards. Buy either a 100 or 200 amp load center. Menards only sells the wire for each application, nothing between. It's up to you how much money you want to spend. I'm betting after you do the math, you will use aluminum. You will need 4 wire for a sub-panel.
After you price PVC conduit, you will not use it.
My power company buries wires and they don't use conduit.
I would only consider using conduit if I had shape rocks in my dirt, which I don't.

Yes, he will need 4 conductor wire between the panels. He needs to determine the load before buying anything and before his question can be properly answered. He doesn't need a 100 or 200 amp panel and wiring if it will only have a couple lights and a charger for cordless tools.

Jim.ME · Oct 8, 2023

Decide on the sub-panel then the wire. With that info you are likely looking at a 100-amp sub panel. You can get 60-amp ones, but they may not have the number of breaker spaces you will want.

Does he have 60 to 100 amps to feed it with?

waugh621 · Oct 8, 2023

Just 60A he is easing in on retiring and
just wants to pluck around on a few things

Jim.ME · Oct 8, 2023

Bear in mind, plasma cutters need a compressed air source so an air compressor and plasma could draw power at the same time. The size of the plasma, air compressor, and welder can add up, but will work on 60 amps if machine sizes (electrical requirements) are matched to the available power. I am thinking you might use the same outlet for the plasma and welder so they wouldn't be in use at the same time, but the air compressor might run when either was in use.

Stephen Newell · Oct 8, 2023

To determine what size wire you would need to add up the amperage of all the thing he might be running at the same time. It would make a big difference if he was only running a small table saw or if he was running a welder. Then at that distance I would go one gauge heavier wire to make up for any voltage drop. Generally the constant voltage draw should be 80% or lower of what the circuit is rated.

Tgrasher · Oct 8, 2023

Geo I put my two 100 ft runs (one to house, one to shop) in 1 1/2 black plastic water line. So far no problems.

John T · Oct 8, 2023

Your question: What gauge wire would we need to run?

When I was practicing power distribution the way I did it in accordance with NEC guidance was:

1) Compute the Maximum Continuous Current

2) Select conductors to have a minimum ampacity no less that 125% of the MCC

3) Compute Line Voltage drop and if necessary (its excessive) upgrade conductor
ampacity

4) Size the Overcurrent Protection Device to adequately protect the Conductors

Conductor ampacity and voltage drop calculators are readily available on the net

You need to choose your wiring method and conductors such as but not limited to direct burial cable,,,,,,,,Conduit with enclosed THWN Conductors,,,,,,,Copper or Aluminum wire.

For 120/240 you need to run 4 wires, 2 Hots, Neutral, Ground and the sub panel needs to have separate electrically insulated and isolated Neutral Buss and Equipment Ground Buss. That buildings electrical service needs to be grounded..

I would install at least a 60 amp much better yet a 100 Amp service to allow for upgrades and equipment.

John T Its electrical so you can expect a ton of responses

DoubleO7 · Oct 8, 2023

Be aware that online wire size calculators can give widely different results.

About three months ago I ran the numbers on seven different online wire size calculators.

Five said 3/0 was needed
One said 2/0 was needed
One said 4/0 was needed

All using the same parameters.

paul · Oct 8, 2023

The code allows a 5 volt drop.

The better voltage calculators on line assume the wires in the building will have some voltage drop, and will allow for a 3 volt drop on that service line.

But different calculators will give different results for sure!

Paul

Check Break · Oct 8, 2023

(quoted from post at 09:59:55 10/08/23) My dad is building a small shop on his proprty and was wanting to run a 220v service to it. The building is roughly 100ft from the source pannel in the house. What gauge wire would we need to run? Thanks nate

First figure out what size you need, then run the largest size you can afford. You'll need it later.

Geo-TH,In · Oct 8, 2023

Each to their own.
Do what makes you happy and I'll do the same.
No right or wrong here.
One time I used a garden hose to run romex to a shed.
I used what I had.
Your idea of using black plastic is better than using solid conduit.
I've never had a straight run.
Today's conduit is more than wire was before the mass inflation.

olddavid · Oct 8, 2023

Interesting you are saying 4 conductors. I'm guessing that's a code requirement. 27 years ago when I ran an entry cable to my mobile home the instructions said 4 wire as well but I couldn't find it. I finally went to one supplier who after I told him the situation said I'm going to give what you need. It was 3 wire. 2 hots and a neutral. It was UF wire and I buried it directly in the ground. #2(?) aluminum cable I believe. I tied the neutral bus and the ground bus together inside the house panel just like I see in regular houses and factory panels that have no separate ground bus and grounded the neutral/ground bus with an 8' copper rod underneath the house. I've had no problems. If I had found 4 wire they would have been connected together in the 100 amp disconnect breaker box at the pole anyway. Not code?

RJKeith · Oct 8, 2023

John T offers good advice. You are trying for 3% drop or less. In general, a #2 wire aluminum or a #3 wire copper will be OK for 100 amps, you usually don't need to upsize until you go beyond 100 feet. Copper is more expensive but is bullet proof, very tough to mess up the installation. For aluminum, if you stress the wire, incorrectly torque the connection, fail to use the right connectors, or fail to use the correct compound, chances are the wire will fail. Might want to get an electrician who does aluminum regularly to help. Don't direct burry aluminum, anything going over the wire that stresses it can cause a failure. If you do use aluminum, put it in conduit. I would recommend conduit for copper as well. Sched 40 PVC conduit is cheap and will protect the wire from soil compaction and soil movement, lessening the likelihood of failure.

JMOR · Oct 8, 2023

How about explaining 20 volt from panel to bathroom with nothing turned on???

Outbuilding wire

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