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Old 11-01-2011, 06:12 PM   #1
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need help with woodshop subpanel


Hello. I need some patient help. I'm sure the info I need is here in the forum. But as my project will be "evolving ", I need one place to keep it all straight. I'm putting an addition on my woodshop early next year. When that happens the old underground wiring (by previous owner) will be replaced. We will add two circuits for 220 then. Until then I must get THE MOST possible out of what's available. Also if possible I'd like to prepare what I can now, so things don't have to be completely replaced. Right now there is a 12/2 wire, from service box, to a small subpanel with two 15 amp circuit / breaker. What should I do? I'd like to at least add a 20 amp circuit for now. With six circuits total, later.What can I do to not only get the most of what's available, but get prepared for down the road? I'm very handy capable, but electrical isn't my strongest area. If I'm told what to do, I will properly and safely. Thanks!

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Old 11-01-2011, 06:29 PM   #2
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Since you say underground wiring, I assume the building is detached. NEC allows only 1 circuit to a detached building. That 1 circuit can be what you have now, or a feeder to a sub-panel or a MWBC which gives you the equivalent of 2 20 amp circuits.

Your first step should be to determine the ultimate load, that will determine what you need. Since you are looking at multiple 240 and 120 volt circuits, you will need a sub-panel.

As far as prep, you could dig the trench and install conduit from the house to the shop. I would suggest 2"; I doesn't cost a lot more than the smaller stuff and will give you flexibility. Bury the conduit to at least 18". You will need 4 conductors in the conduit; wiring sizing will be based on the load calculation and length of the cable run.

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Old 11-01-2011, 06:57 PM   #3
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need help with woodshop subpanel


Sub panel in wood shop

I would supply it with a minimum 220v 30 amp sub panel - that would cover you for lighting , compressor and some shop equipment.

you could use direct buriel tech cable 10/4

18 inches at least
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Old 11-01-2011, 07:39 PM   #4
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Yep, the shop is detached. Unfortunately I can't bury the new cable until the addition is put on. This goes under a fenced in area ,that will be removed. The existing buried wire is 12/2. It runs to a small sub panel that has two 15 amp breakers. What is possible at this point? Can I add a 20 amp breaker? Or change the 15' s for 20's. If so what size breaker should I replace in the service panel?
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Old 11-01-2011, 07:45 PM   #5
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You have 12/2? So you only have 120 volts at the shop. But you have 2 breakers in the shop and at the main panel? You can change the breaker at the main to a 20 amp, since you have 12 guage wire. What are each of the two 15 amp breakers for, since they are on the same circuit, same phase?
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Old 11-01-2011, 08:11 PM   #6
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The breaker in the house panel that the 12/2 is on, is it a single pole or a double pole? Do you have ground rods at the shop?
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Old 11-01-2011, 08:41 PM   #7
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need help with woodshop subpanel


Wow! I just checked to verify the previous work a little closer. It looks like 12 gauge goes from service panel,to a junction box that connects to the wire that goes underground. From the junction box 10/3 runs to the shop, to a panel with two 15 amp breakers. The shop is wired with the 12/2. This is a hodgepodge mess.

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Old 11-01-2011, 08:42 PM   #8
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And no ground rods. Double pole breaker. Where to start?

Last edited by pdoubleu; 11-01-2011 at 09:07 PM.
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Old 11-01-2011, 10:03 PM   #9
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Your options are severely limited until you can get more power out to the shop.
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Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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Old 11-01-2011, 10:36 PM   #10
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And no ground rods. Double pole breaker. Where to start?
If it is a double pole twenty amp, you can change the other shop breakers to 20 amp if the the shop wiring is 12/2. This only buys you a few more amps.

But as Jim said above me, you only do so much with what you have.
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Old 11-01-2011, 11:38 PM   #11
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need help with woodshop subpanel


Harvey Holzman's guides available on Amazon will give you an excellent start on planning your success. They have pictures and diagrams that help the DIY as well as professionals put the NEC into action. Additional I found several other guides to residental electircal wiring illustrated on Amazon and Ebay. I have rewired and repaired several houses, garages, mills, etc, and each one is unique. Using Direct burial MC,Armor,SOOW or equivillent is helpful. Hopefully your existing conduit will allow you to pull bigger wire, but I'll bet you want at least #4/2 with ground or 4/3 to service your new shop. Planting conduit and pulling wire can get expensive and cumbersome real fast.
Good Luck
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Old 11-02-2011, 04:41 AM   #12
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Discussion of wire sizing is moot until you do a load calculation and determine the distance of the run. Once you determine the sub panel feeder sizing you need to determine if the house panel has enough capacity to supply it.

Direct burial wiring for a sub panel must be at least 24" deep
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Old 11-02-2011, 09:00 AM   #13
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Ok so now I've got 10/3 coming from a 20 amp double pole, to a junction box, to the shop. From there a small box with two 15 amp breakers. Should I replace this so there's a main breaker switch, and get the box ill need in the future?

@code05. Can I safely switch the current breakers to 20 amp, and are two the Max for the current setup? P.s. Easton is amazing!
@Jim Lee SR. I will absolutely pick up that book! Mine is very inconsistent. So now I just ask electrician friends What to do, and I'm missing the details. Thanks for the great input.
@Rjniles. When the renovation gets closer I will total the load. I've gotta live with what I have for now, while still working. Though I don't need much else, besides two 240 outlets. One for heat, other for a planer. Half my work is by hand.


Thanks for all the help, and your patience.
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Old 11-02-2011, 09:42 AM   #14
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Quote:
Originally Posted by pdoubleu View Post
It looks like 12 gauge goes from service panel,to a junction box that connects to the wire that goes underground. From the junction box 10/3 runs to the shop, to a panel with two 15 amp breakers. The shop is wired with the 12/2. This is a hodgepodge mess.
You said there is 10/3 connected to #12 from the panel. 10/3 will have a black, red, and white conductor. How is this connected to the #12? Is it 12/3 or 12/2?
The #12 limits the circuit to 20 amps. How far from the panel to this J box?
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Old 11-02-2011, 10:17 AM   #15
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Great questions. I meant 12/3 from service to jbox,10/ 3to shop,12/2 in shop. Sorry. I read that this morning and realized how long my day had been. So. 12/ 3 goes from service panel down 4ft, then theres a jbox that has 10/3 running from through conduit, to shop box. 12/2 throughout shop. So cant i replace the 12/3 with 10/3? That would make it 10/3 all the way. I dont know if they just got lazy with the 12/3. Its only a few feet. So how will the change help? What to do next?

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