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I have about a 75 foot run and have some spare copper 1/0 (1) wire so would like to save on buying something different.

Is this usable to tie into main panel lug, trench it in conduit and tie into a square D sub panel for my woodworking shop?

The shop is 12 x 16 and I plan on 3 or 4 - 20 amp breakers. One for AC, two circuits for equipment and lights.

I will use 12/2 for inside the shop.

Is there a better way to do this?

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    Can you post the markings on said spare wire? Jan 10 at 5:05
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    " 1/0 (1) wire" is a little confusing. 1/0 and 1 are two different sizes. 1/0 (one aught) is size 0, 1 is the next size smaller. 2/0 awg (two aught or 2/0) is the next size bigger. Jan 10 at 17:51
  • @NoSparksPlease I think the "1/0 (1) wire" means "1/0 AWG size wire but individual wire as opposed to 12/2 which is a 2-wire (plus ground) cable made of 12 AWG size wires". And I wrote my answer based on that, for better or worse. Jan 11 at 3:27

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A few different issues here:

  • Wire Size

1/0 copper is good for up to 150A, which is far more than you are likely to need based on the description of the project.

Normally you would use smaller ground, and possibly smaller neutral, than the hot wires to save some money. But if you've already got the wire, that should be fine.

  • Wire Type

The wire needs to be marked for wet use, such as THWN or XHHW.

  • Wire Color

As I understand it, and confirmed in this online article with 4 AWG or larger you can mark a non-white wire as white on the ends to use it as neutral. Based on this article you can do the same for ground with green tape. So if your 1/0 wire is all black, mark the neutral and ground and you should be OK.

  • Feed Breaker

You can only connect to panel lugs if you are using wire capable of taking the entire panel feed. Which basically means it won't work here. If you have a 200A feed and a 200A panel then you would need 2/0 (83% derate for full utility feed), not 1/0. If you have anything less than a 200A feed then you are likely to run into Load Calculation issues. So don't use lugs, use a feed breaker (50A, 60A, 90A, etc.) to match your wires and anticipated load.

  • Load Calculation

Any time you add significant loads, you should do a Load Calculation. This is a complex formula that takes into account the size of your buildings, required dedicated circuits (kitchen, bathroom, laundry, etc.), HVAC, large appliances (water heater, cooktop/oven, etc.) and any other known special loads (e.g., EV charging). This is primarily based on your utility feed but may also be needed at the subpanel level to make sure you have sufficient capacity at each step of the way.

  • Conduit Size

Based on the Southwire Conduit Fill Calculator with 4 1/0 wires you will need at least 1-1/2" conduit (based on PVC Schedule 40, other types may vary). Using a more typical Aluminum 2 AWG x 3 + 4 AWG x 1 (ground) you could use 1-1/4" conduit. If you used smaller wire (e.g., Aluminum 4 AWG, max. 65A) then you could use 1" conduit.

All that being said, larger conduit isn't a bad thing as it allows for expansion. (Though if you stick with 1/0 copper you will likely never need expansion past 150A.)

Burial depth depends on conduit type. Direct burial cable is available as well, but that goes even deeper.

The general recommendation is to use aluminum. You might even find that you could sell the copper (it is both more expensive than aluminum in general and a much larger size than you need), buy aluminum wire and have some money left over to spend on conduit, subpanel, etc. If you do that, 2/2/2/4 aluminum is the typical recommendation, which can handle up to 90A, which is still far more than you need.

  • Ground Rods

You need 2 ground rods connected to the subpanel. That is in addition to the ground wire going back to the main panel.

  • Disconnect

You need a disconnect at the shop. The easiest way to do that is with a "main" panel instead of a "subpanel". The key differences are a main breaker (can be much larger than the feed breaker, that's OK) which you use as a disconnect and that you need to make sure to not bond neutral and ground.

  • Big Panel

Even though you only need 3 or 4 circuits right now, get a big panel. A big main panel often costs very little more than a small subpanel. Look at "spaces" and not "circuits" because most, if not all, of your circuits will require AFCI and/or GFCI and those breakers are often only available for full-size spaces. While you might think an 8-space or 12-space panel will be big enough, it is much better to spend a little more for a 20 or even 30 space panel and never have to worry about more space.

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    thanks, my 1/0 is Sim pull t90..... THWN. For your wire color comment, do I need to run other wire to my shop because the 1/0 is just a single copper wire? If so, i would prob be better of getting aluminum 2/2/2/4 and installing a 100Amp on my main panel. Typo on the 12/2, thanks and thanks for the other recommendations
    – Wallace
    Jan 10 at 5:25
  • You need 4 wires hot, hot, neutral, ground. 2/2/2/4 is good to 90 A as a subpanel. So breaker in main panel for feeder max 90 (can be smaller) subpanel can have a 100 or even 200a breaker as that is just for disconnect. Jan 10 at 6:05
  • Huh... wonder why the down vote... :/
    – FreeMan
    Jan 10 at 12:56
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    @Wallace what do you mean by "tying into the main panel lugs?" Can you post photos of your main panel please? Jan 11 at 3:24
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You can use that overkill 1/0 copper, but why on earth would you? It will fetch more on Craigslist than the right aluminum wire even costs new.

I would use 2-2-2-4 aluminum, as it's in a sweet spot between price and availability. Aluminum is proven safe for a heavy feeder like this. 90A wire is overkill for your needs, but you won't save much money on any other type of wire. #6 aluminum (50A) isn't that much cheaper and makes some people nervous.

It can fit on any breaker 70A or larger. (Larger breakers are more expensive). The 60A breaker of most breaker types will also accept #2 wire, and the breaker is cheaper.

If you run conduit the entire way, (this must be built empty and the wire pulled in after it is complete and signed off)… you can use THHN or XHHW wires inside the conduit.

If you want to direct bury, use 2-2-2-4 aluminum MH feeder and run conduit where it is inside the building.

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What exactly do you mean by " tie into main panel lug?" If you are installing a breaker into main panel, that is fine. If you are trying to stuff new wire into same lugs as feeding main panel, then definitely not.

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