# What Size Wire For 40 Foot Run To Shop From Main Panel To Add 220 To My New Shop?



## John Caven (Mar 5, 2015)

Ok so i just got a lathe and a mill and am building a new shop.  What size wiring do I need?   I've done normal home wiring but I'm not sure the size for a job like this.  I plan to use a rotary converter!


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## jim18655 (Mar 5, 2015)

How big of service do you want in the shop?


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## extropic (Mar 5, 2015)

First, you need to decide the amperage required/desired in your new shop. It's difficult to have too much power available. The wire is sized to carry the amperage over the distance.  It's called ampere capacity (or ampacity for short). Easily Googled.

Also involved is the viability of the source of the power. If you plan to run a 50 amp subpanel from the ancient 100 amp panel on the house, you may start browning out the house.

More information is needed about your circumstances to provide an intelligent answer.


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## rsegars (Mar 6, 2015)

John Caven said:


> Ok so i just got a lathe and a mill and am building a new shop.  What size wiring do I need?   I've done normal home wiring but I'm not sure the size for a job like this.  I plan to use a rotary converter!


I have found wiring guides on the net(google) just enter the numbers and the length of the run and it will calculate wire size for you.


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## Mark in Indiana (Mar 6, 2015)

The 40' length is not going to be a concern. What is the amperage or current of the equipment that you plan to run in your shop?


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## calstar (Mar 6, 2015)

Always better to have too much than too little capacity , but consider how many machines/appliances will be running at the same time, that's the main consideration.
I ran #6 copper 40' +- to a new sub panel  in my garage/shop a couple yrs ago, probably over kill as I most likely will never come close to using the full load capacity  at the same time.
The largest "power user" is a 50amp ac/dc welder.

Brian


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## aliva (Mar 6, 2015)

Allow for the largest machine you'll ever run + lighting.
Not likely you'll ever have a mill, lathe , compressor, welder, running at the same time.
I ran # 2 CU 60 feet to a 100 amp panel. Way more than I'll ever need, but I'll never have to dig it up to go to a larger wire size either


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## mzayd3 (Mar 6, 2015)

If you are running conduit, bury a few extra 3/4's.  You may want to add switches and stuff


Sent from my iPhone using Tapatalk


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## calstar (Mar 6, 2015)

_"The largest "power user" is a 50amp ac/dc welder."
_
Forgot to add that's running at max capacity, won't ever need to use it that way, not a ship yard, just a small shop.

Brian


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## John Caven (Mar 6, 2015)

how much is 40 feet of # 2?  I'm trying to find the best place to buy cable.   I too like overkill


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## John Hasler (Mar 6, 2015)

aliva said:


> Allow for the largest machine you'll ever run + lighting.
> Not likely you'll ever have a mill, lathe , compressor, welder, running at the same time.
> I ran # 2 CU 60 feet to a 100 amp panel. Way more than I'll ever need, but I'll never have to dig it up to go to a larger wire size either


Also a waste of money to run copper.  You won't see a power company doing that.


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## aliva (Mar 7, 2015)

I don't trust aluminum and I got the copper for free


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## mksj (Mar 7, 2015)

There are a number of considerations as to what wire you use and how you want to run it. If you are pulling through conduit, I prefer soft annealed copper wire, if you are doing direct burial or overhead, then use aluminum service entrance/direct burial type. A 100 amp breaker/sub panel, you would use 4AWG copper, 2AWG aluminum x 3 (neutral can be 1 size smaller), and a ground wire of at least 8AWG copper,  or 6AWG aluminum. You want to make sure the wire is rated to 90C and also all the connections/breakers are also rated to this temperature. This may sound trivial, but often connection may be rated at a lower temp, and you need to derate the system. There also may be some derating for direct burial vs free air service entrance wire size. Code may vary a bit, conduit size for a 100A service is 1.25" Cu, 1.5" Alu. Voltage drop is about 0.8% for the size wire specified over 40 feet. Either wire would work, what you use depends on how you want to pull it, the cost difference at this level is minimal. Aluminum becomes a lot cheaper as you go to larger gauge wire. Terminals must be rated for aluminum, and I use a electrical gel on the wires which prevent corrosion.  Also be sure to mark the wires at both ends before you pull it to denote red-hot (L2), white-neutral, green-ground (if wire is not already green).

I put in a 100amp sub panel service to my garage, it is about 38' from my main breaker box. I used a 1.5" plastic electrical conduit (a bit bigger than required, but easier to pull wire), and use three 4AWG copper THHN wires (1.19/foot at home depot), and one copper 6AWG THHN green ground. There is no reason to go bigger, if you have a 100 amp service. You can pull off both 240V and 120V on separate breakers in the sub-panel, so you should not need to pull any other wires in the conduit coming from the main breaker.


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## hcdozier (Mar 12, 2015)

One thing I have NOT seen mentioned and that is making sure that the grounding is good for any subpanel.

I ran CU#2 (3 wires) to my 100A subpanel in the utility barn I have for a shop.  Only about a total 25 foot run, but overkill is not only recommended, but a safety factor as well to assure myself and wife that nothing would overheat in the runs under any circumstances.  I buried it 30" below ground level and also placed a series of salt treated timbers on top for safety for the future.

Then I also through the same 1 1/2" plastic conduit pulled a CU#4 ground wire.

The subpanel is UNBONDED, meaning that although the 3 CU# 2 wires are connected to the two bus sides and neutral, the grounding bolt is removed so that there is a separate ground for the barn to a pair of ground rods in the earth outside near the load center panel.
The CU#4 from the house ground connects to the subpanel ground, which then connects to the two local ground rods.

This places all grounds together at the same potential so no loops.

Then the subpanel provides both 220V 1-phase and 110V (using the common neutral back to the main panel).  That is sourced from a 100A breaker in the main panel.  The subpanel "main" is a local 100A breaker for the whole panel.

This is what the NEMA code specifies for subpanels.

Hank


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## Eddyde (Mar 12, 2015)

John Caven said:


> how much is 40 feet of # 2?  I'm trying to find the best place to buy cable.   I too like overkill


I just ran a 100 Amp sub panel with 2,2,2,4 (2 hot legs, 1 neutral & 1 ground) aluminum cable from Home Depot, cost less than $2 a foot here in NY.
Be sure to use anti oxidant paste on the connections.


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