Upgrading Wiring - Questions about correct sizing


Old 03-25-12, 05:22 PM
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Join Date: Mar 2012
Posts: 1
Upgrading Wiring - Questions about correct sizing

Hello all

I have two shops in back that I want to upgrade the wiring currently running to them. Currently there is a 12g wiring that is running from the main outside box to one shop and from there branches out. Right now I have 1 Refrigerator in the first shop. Wife uses second shop for building props, so lighting and power tools use there.
There are two outdoor lights that will need to have power (the home "street light" type)

Plans: Run new wiring to same shop, install a breaker box and then upgrade the wiring to second shop and two outdoor lights. I want to be able to have a second Refrigerator in my shop and would like to install a window unit AC in wife's shop. I am trying to decide between using a 10-2, or a 8-2. The 10 will give 30 amps, the 8 will provide 40 amps. I think I will have to use the 8 mainly because of the AC factor. If we decide not to have the AC, will the 10 be ok?

Also what if I used a 10-3 and then a two pole breaker box, and have a pole for the second shop? Would that work?

Thank you in advance for your input

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Old 03-25-12, 06:09 PM
Tolyn Ironhand's Avatar
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Join Date: Nov 2007
Location: Twin Cities, MN
Posts: 12,285
Welcome to the forums Ray!

Lets start with some basics. You should run 240 volts out to your shops. This will give you double the capacity with just a little more cost. This means you will need to run 4 wires to the shop. 2- hots, a neutral and a ground. You will also need a ground rod at each shop with tied to the panels (more on that later) Each panel will the ground and neutrals separated. Do not bond the neutral to the panel can.

Other then the fridges you didn't mention anything else in your shop. Your wife's shop sounds like the larger of the two loads. I like to cover all the bases so I would suggest this route. It will give you the most bang for the buck:
60 amp, two pole breaker in your main panel
#6 copper or #4 aluminum wire to first shop
Install a 100 amp 20 circuit panel in first shop. About $50. Or you can go smaller but cost wise you will save almost nothing unless you go with a 6 circuit which I think is too small.
Install another 60 amp two pole breaker in the first shop panel.
Run the same wire you ran before (#6 copper, #4 aluminum) between the first shop and the wife's shop.
Install same panel in wife's shop

This will give you 60 amps total between both shops and 240 volts in both shops. You could go #8 and a 40 amp but you will be giving up 20 amps of capacity for really only the cost savings of the wire.

IF you still want to skinny up more then #10 and 30 amp breakers is an option. You will save on the wire, a small amount on the breaker (maybe) and still have 7200 watts of power available. You can still use the same panels as they give you the most flexibility but you could save a bit more going with the smaller panels I mentioned. Or maybe you could put one bigger in your shop and the smaller one in the wife's.

Just remember you may have only one feed to a separate building. Price it out and see what your budget can handle.

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