12/2 or 10/2 -- 220 general purpose outlets

[Bob Cooper]

Wiring the shop and from posts i've read that many folks have commented that one thing they should have done differently was to run more outlets...both 110 and 220.

So i'm going to run a good many around the shop and i was planning on running 12/2 but just want to make sure there's no reason i shouldn't run 10/2. The recepticles will only be 20A and i don't really plan on plugging the table saw, planer (it's 3 phase), or dusk collector into it. I probably will plug the 8" jointer into it but i really don't have that many other 220 items. So it seems to me 12/2 is fine but it's easier to ask now in case i'm missing something.

note -- for the table saw i'm planning on having power come up through the floor in the middle of the shop; the dust collector will be in another room; both of those will be dedicated circuits.

[Mike Cross]

12/2 for 20 amp breaker, 10/2 for 30 amp breaker. Looks like since you will be using 20 amp circuit 12/2 is correct. Wire to the breaker size.

Mike

[Erich Weidner]

12/2 for 20 amp breaker, 10/2 for 30 amp breaker. Looks like since you will be using 20 amp circuit 12/2 is correct. Wire to the breaker size.

Mike

That being said, you might choose to run 10/2 if you want the flexibility of just changing out the breaker to a 30A if your needs change someday. I am wishing I'd done so in my garage. The savings in $$ was not worth the "joy" I now get to experience again (by going into the attic and swimming through insulation).

[Jim Sebring]

When I built my shop 5 years ago I put 110v quad boxes on every-other-stud, with 220v outlets on the intervening studs. Have three ceiling 110v drops, and 3 220v drops for the tablesaw, 8" jointer and planer. I only wish I had known where all the gear was gonna be placed. Should have run more circuits. 12-2 works for nearly everything.

[Jerome Hanby]

I ran 10/3 on duplex 25 amp breakers and wired the outlets duplex (one circuit on top, different one on bottom). Didn't change the cost very much and lets me do things like plug the router table and dust collector into the same outlet fixture without overloading either circuit. That 10/3 is pretty stiff and I got a good workout getting everything tucked away into my electrical boxes, but that's a one time effort. My sub panel is close to the middle of the back wall, so I ran one duplex circuit around and to the left, another around and to the right, dropping 5 outlet fixtures off each one just to give me an outlet handy anywhere along the wall of the shop. Also wired a drop 240 and a drop 120 duplex over the island where my table saw, planer, jointer, and big dust collector will live. I can always rewire that duplex to be another 240 in the future if I need one. I also went ahead and used 25 amp outlets. They have that funky cross piece for one of the prongs, but regular 15/20 amp plugs still fit.

[Bernie May]

When I rewired my garage shop, I used 10-2 for all my 220 lines except for an 8-2 for the possibility of an arc welder or something really big. I ran five of the 10-2 lines. One for the electric heater and one for the dust collector that can both be on when some other tool is on. Glad i put in 10-2 versus a mix of 12-2 and 10-2 when I changed my mind about where to put the electric heater. Just had to change the plug and breaker. I did tend to use larger boxes to make working with the stiffer 10-2 easier. The big unknown is will you someday have a tool with a motor larger than 3 hp. If you do, you will be so glad there is 10-2 in place, especially if your lines are buried in the walls or ceilings.

[Kent A Bathurst]

The big unknown is will you someday have a tool with a motor larger than 3 hp. If you do, you will be so glad there is 10-2 in place, especially if your lines are buried in the walls or ceilings.

Yep. Or, in my case, I replaced some tools with bigger-HP versions, and the 10/2 let me simply change out the breaker to 30a, and keep the same circuits in place [2 machines on one circuit]

Also - Bernie's point about bigger boxes is spot-on.

EDIT: Also - FWIW: I ran 10/3 plus ground, so I could use split-voltage duplex receptacles in a couple spots.

[Darrell Bade]

I ran 12-2 for all my 110 & 220's. I did however only put one outlet per circuit on one wall so that with some changes in the box putting more than one outlet on a circuit a 220 could be added in the future. I did not load any of mine with more than two or three outlets per breaker. Overkill I know, but I had the capacity in the box.

I used the 12-2 because I did not plan on having any 220V equipment with over a 3 HP motor which only requires a 20 amp breaker and 10 ga wire is really expensive. I already decided to add a widebelt sander and have added aother outlet with a 50 amp capacity.

If I had it to do over I would run all my 220's with 10 ga. It just gives the opportunity to get something bigger with a 5 hp motor if you ever want to.

Guess it really depends on what the funds for the project are like.

[Dan Case LR]

You can never go wrong by up-sizing wire. Not only does it give you easy upgrade possibilities in the future, but the voltage drop on longer runs will be lower. That said, if you're using a 20A breaker and typical wire runs, #12 will serve.

HOWEVER.... please indulge me as I vent over one of my wiring pet peeves.

It worries me just a little when I see discussion of running 12-2 (or 10-2) for 220V circuits. Here's why: those 2 conductor with ground non-metallic cables are color coded black/white. I've seen a whole lot of installations using it for this purpose, and almost universally the white wire is left white, which is the color code for the Neutral (grounded) conductor. At some point, that cable will join other cables either in a junction box or in the breaker panel where there are 120V circuits that use the white for neutral. Now you've got whites wires doing two very different jobs, and you set up a possible safety hazard--not for you, because you know what you did. The hazard is for the next guy who has to work in there after you're gone.

The NEC prescribes a very simple way to remedy this situation: Stripe the white wire used as a hot conductor with red tape. Failure to do this will cause an electrical inspector to fail the installation. I believe we ought to wire our stuff to code, as though it had to pass inspection, even if it doesn't. There's a good reason behind every point of the electrical code, and that reason is always safety and fire prevention related.

Okay, I'm done venting.

D.

[Steve Meliza]

10/2 is expensive and stiff compared to 12/2 and for a 120V circuit you'll never have a need for more than 12/2 unless you think you'll some day re-purpose the circuit for 240V then it may be worth considering 10/2. Your choice also depends on accessibility, if the wire is buried in the wall then a little up front expense and hassle may be worth it. If the circuit is to be 240V from the get go then you may as well install 10/2, even if you use a 20A breaker and outlet.

In my case I've run all the wire through conduit so any changes to the wiring is easy and it was cheaper to buy 500' spools of #12 THHN rather than mix #12 with a little #10 "just in case". I also found that making up something like 60 splices and wiring 20+ outlets with #12 wire was a pain enough that I can't imagine doing it all with #10 wire. Not to mention some of what I wanted to do would have required up-sizing my EMT to 3/4" and installing junction box extension rings to meet fill requirements. As it is I have enough fill space to up-size one circuit in each conduit run to #10 if needed.

Regarding using NM 12/2 or 10/2 for 240V, around here it is common practice to wrap black tape around the white wire to indicate it is no longer a neutral wire.

[Dan Case LR]

Regarding using NM 12/2 or 10/2 for 240V, around here it is common practice to wrap black tape around the white wire to indicate it is no longer a neutral wire.

Black tape is also acceptable--anything but white, green, blue, yellow, or orange, which all have particular uses.

D.

[Rod Sheridan]

If you're using 20 ampere breakers run 12/3 from a 2 pole 20 ampere breaker and wire it as a multi-wire branch circuit.

I did that with my shop and each 4 inch square box has a duplex 240V receptacle and a duplex 120V receptacle split. It's great, it gives you 2 X 20A circuits at 120V and 1 X 20A circuit at 240V.

For a home shop it's the most efficient way to wire the receptacles for your machinery and convenience outlets.

You'll also need a circuit for your dust collector (Unless it plugs into one of the 120V receptacles).

Regards, Rod.

[Dan Case LR]

If you're using 20 ampere breakers run 12/3 from a 2 pole 20 ampere breaker and wire it as a multi-wire branch circuit.

I did that with my shop and each 4 inch square box has a duplex 240V receptacle and a duplex 120V receptacle split. It's great, it gives you 2 X 20A circuits at 120V and 1 X 20A circuit at 240V.

For a home shop it's the most efficient way to wire the receptacles for your machinery and convenience outlets.

You'll also need a circuit for your dust collector (Unless it plugs into one of the 120V receptacles).

Regards, Rod.

I respectfully disagree, Rod. There are two issues here that are code violations:

1) The neutral isn't properly sized. In the case of your two 120V circuits, if both were drawing 20 Amps, the neutral would be carrying 40 amps, 200% of its rated ampacity. It would be quite possible for the 120V circuits to be carrying enough current to cause the neutral conductor to catch fire without tripping the breaker.

2) Your 220V circuit requires that both poles of the breaker be ganged together. I'm fairly certain that most codes won't allow deriving 120V from one side of a ganged breaker unless there's another protective device (breaker or fuse) in the 120V circuit.

While this will "work," your saw will "work" without an equipment grounding conductor (safety ground)--until the motor winding shorts to the frame and instead of popping the breaker it pops you. Like I said, there's a good reason behind every electrical code on the books.

D.

[Steve Meliza]

I respectfully disagree, Rod. There are two issues here that are code violations:

1) The neutral isn't properly sized. In the case of your two 120V circuits, if both were drawing 20 Amps, the neutral would be carrying 40 amps, 200% of its rated ampacity. It would be quite possible for the 120V circuits to be carrying enough current to cause the neutral conductor to catch fire without tripping the breaker.

The double pole breaker ensures both 120V circuits are 180 degrees out of phase so the neutral wire carries 0A when both circuits are equally loaded and a maximum of 20A when only one of the circuits is fully loaded and the other has zero load.

2) Your 220V circuit requires that both poles of the breaker be ganged together. I'm fairly certain that most codes won't allow deriving 120V from one side of a ganged breaker unless there's another protective device (breaker or fuse) in the 120V circuit.

What code requires is a 2-pole breaker so that if one circuit trips they both trip so you don't end up with voltage on the neutral wire in a circuit box you thought was dead. The suggestion is perfectly valid and is used all of the time. Multiwire branch circuits do have other disadvantages, but the economics of it tends to make the decision for most people as it is cheaper.

[Rod Sheridan]

I respectfully disagree, Rod. There are two issues here that are code violations:

1) The neutral isn't properly sized. In the case of your two 120V circuits, if both were drawing 20 Amps, the neutral would be carrying 40 amps, 200% of its rated ampacity. It would be quite possible for the 120V circuits to be carrying enough current to cause the neutral conductor to catch fire without tripping the breaker.

2) Your 220V circuit requires that both poles of the breaker be ganged together. I'm fairly certain that most codes won't allow deriving 120V from one side of a ganged breaker unless there's another protective device (breaker or fuse) in the 120V circuit.

While this will "work," your saw will "work" without an equipment grounding conductor (safety ground)--until the motor winding shorts to the frame and instead of popping the breaker it pops you. Like I said, there's a good reason behind every electrical code on the books.

D.

Dan, Steve already answered the isuue of the neutral current and why a double pole breaker is used.

I'm an Electrical Technologist and I think you'll find that your home already uses multi-wire branch circuits, such as in the kitchen counter receptacles.

regards, Rod.