Need opinions on shop wiring

[Doyle Alley]

I'm getting ready to run all the wiring necessary to convert my garage into a proper shop. There will be the required mixture of 220 and 110 circuits - no help need in that department.

What I'm looking for is help in the "economy" department. For the 110 circuits, I'll need 12-2wg NM. For the 220, I'll either need 12-3wg NM or the special 12-2 stuff that has red and black conductors instead of white and black (I don't want to risk using white wires as the live conductor in a 220 circuit ). I've been thinking about skipping the 12-2 and just buying a big roll of 12-3. On the 110 circuits, the extra colored conductor would just be unused (and not connected to a breaker). On the 220 circuits, the extra white conductor would be unused at the outlet end, but tied to the neutral bus bar in the panel. I'm thinking that this would allow me the flexability to convert an entire circuit to 220 or 110 as my shop layout changed.

Any thoughts on this approach?

[Chuck Saunders]

Sounds fine Doyle. nice to have the flexibility waiting on you.
Chuck

[Larry James]

Better get some professional advice on the wire. 12-3 will not have the current carrying capacity for 240 volt circuits. Suggest wiring 120 volt circuits with 12-2 and 10-3 for 240 volt circuits. The best answer is “depends.” The connected loads and wire length determine the wire size.

Also, search SMC for “electrical wiring” .

Larry

[Cliff Rohrabacher]

for the shop light power consider separate set of breakers and 14-2wg. A fistfull of flourescents doesn't warrant 12-guage - - unless it's cheaper not to purchase a separate coil.

[Doyle Alley]

for the shop light power consider separate set of breakers and 14-2wg. A fistfull of flourescents doesn't warrant 12-guage - - unless it's cheaper not to purchase a separate coil.
I'm thinking overall economy here. I'm betting it would be cheaper to buy a big roll of 12-3wg than piecemeal the various sections. Actually, my light circuit is staying as-is. I've got one 20A 120 circuit going to the garage now. I've got an un-connected 6-3wg that will service the subpanel for the new wiring. I plan on using the original 20A circuit for the shop lights. That way, if something blows the main breaker at the subpanel, the lights will stay on.

As far as needing 10 gauge for the 240 circuits, that would be overkill for my needs. The 220/240 machines that I have or will have should do fine on 20amp circuits as I don't plan on running any two of them at the same time (except for the dust collector which will use a dedicated circuit).

[Edward Carrion]

:) I agree with Larry on the wire sizes, also you need to match the breakers too. I am in process also of doing electrical and found that it is best for you to check with your local planning commission and see what version of the NEC (National Electrical Code) they are using mine is still on the 2003 version. This will save you a lot of headaches and should you ever have an electrical fire your'e insurrance does not have an excuse of not paying.

The other thing I did was to determine my loaded amps this does not mean how much the tools draw when operating but how much they load the circuit on start up and under its maximum load rating in amps . The tool manufacture may not know this but the motor manuf will. I then took this data to a COMMERCIAL electrician and he calculated my wire, circuit size, and number of dedicated and shared 110's and 220's I needed.

[Jeff Horton]

12 ga is rated for UP TO 20 amps. Doesn't matter if it is 110V or 220V.
14 ga is rated for UP TO 15 amps

I think your going to find that 12-3 is a lot pricer than 12-2.

12-2 can be run as 220V. As for white wire being a hot, by code all you have to do is place mark it black. Like electrical tape or a sharpie.

It's quite common wiring a house to have a white wire that ends up being hot for some reason. I am not sure that is ever required in 220V because it is so obvious the way it is wired. But double check me on that.

If you do go with 12-3 just make sure you leave space to replace 110 breakers with 220 and that leave enough wire in the cabinet to move them around if you do change a breaker.

That way, if something blows the main breaker at the subpanel, the lights will stay on.
Very smart! When I wired my house no outlet was on the same circuit as the a light. Same reasoning.

[James Suzda]

Just use 12/2 wg for the 240 circuits. You can use a red felt pen to color the white wire, or use some red car touch-up lacquer paint. (It even comes with a handy little brush in the cap)
Don't forget to use 240 volt receptacles!!!
Jim

[Larry James]

I'm thinking overall economy here. I'm betting it would be cheaper to buy a big roll of 12-3wg than piecemeal the various sections. Actually, my light circuit is staying as-is. I've got one 20A 120 circuit going to the garage now. I've got an un-connected 6-3wg that will service the subpanel for the new wiring. I plan on using the original 20A circuit for the shop lights. That way, if something blows the main breaker at the subpanel, the lights will stay on.

As far as needing 10 gauge for the 240 circuits, that would be overkill for my needs. The 220/240 machines that I have or will have should do fine on 20amp circuits as I don't plan on running any two of them at the same time (except for the dust collector which will use a dedicated circuit).
Doyle,
Since you have a 6-3 line to the garage sub-panel, how much more would it cost to use 10-3 for 240 outlets? Are you assuming 20 amps is adequate based on name plate data from the 240 tools? What about motors starting or running under load. If you use 10-3 with a 20 amp 240 volt breaker, and later find that it is not adequate, you would only need to increase the breaker size.

As a rule of thumb, multiply the highest amp draw tool load current by 1.25. If that is near or exceeds 15 amps, or 75% of 12 ga capacity, you should consider 10-3. In his post, Jeff Horton correctly points out- "12 ga is rated for UP TO 20 amps. Doesn't matter if it is 110V or 220V." Notice he has “UP TO” in caps.

How big is the garage? If you have a sub-panel and lighting is on a separate circuit, how much wire could you need??? Using 12-2 for 120 volt outlets and 10-3 for 240 volt outlets from the sub-panel is not over-kill. The cost would be worth the added margin of safety.

IMHO, Larry

[Ken Garlock]

Doyle, what gauge wire you use is dependent upon the load for which you are wiring. I ran 30 amp 10-3 plus ground for my cabinet saw and jointer. along the walls I have 12-2 plus ground for 20 amp 240v outlets for the bandsaw and other 'smaller' tools.

My 120v wall outlets are dual duplex outlets with each duplex outlet on a separate circuit from its mate. That is easy to do with a single 12-3 plus ground 240v drop. One hot side to neutral is one 120v circuit, and the other hot side to neutral is the other circuit. The inspectors never blinked an eye....

[Rick Christopherson]

Doyle, I would not recommend using 12/3 for all of your wiring. Deliberately abandoning a conductor for every circuit is not a good practice, especially when the reason behind it is so you can have the color coding. The abandoned conductor will have an induced voltage on it from the other conductors, so both ends must be wire nutted at every box.

It's not like someone will be servicing these outlets on a monthly basis. Once they are installed, it is likely they will never be touched again. However, you will cause greater confusion for a future owner by having an aboandonded wire in every box than by having a white-coloered hot.

Larry, Please don't present your electrical advice as though it was factual without having the proper foundation. This is a disservice to these discussions, and is the root cause for so many electrical myths on the internet. Doyle already told you he did not have large current drawing tools, but you needed to reiterate your misinformation a second time, and in more "detail". If all of his tools are 3 hp or less, there is nothing gained by going to #10 wire.
....12-3 will not have the current carrying capacity for 240 volt circuits.

[Doyle Alley]

Thank you all for your valuable advise. I'm in the process of mapping out my wiring layout now to determine how many feet I need. Once I get that done, I'll be able to get prices by the foot, by the box, and by the roll, etc. As far as amperage draw is concerned, by biggest "dream" tool would be a 3hp cabinet saw. Grizzley recommends only a 20amp breaker for it. The other 240v tools would be a dust collector (1.5 hp) on its own line, a window A/C on it's own circuit, and an air compressor that is currently wired for 110 but frequently pops the breaker. Some other 120/240 convertable tools might get wired for 240 just to balance the load as seen by the subpanel breaker. Those would run on the same circuit as the table saw because I could only have one at a time turned on. The dust collector, window A/C, and compressor would all run simultaneously with the table saw (or other "tool") so they are going to be wired separately.

[Charlie Velasquez]

My 120v wall outlets are dual duplex outlets with each duplex outlet on a separate circuit from its mate. T...<snip>.. One hot side to neutral is one 120v circuit, and the other hot side to neutral is the other circuit. The inspectors never blinked an eye....
Ken,
I wanted to do something similar and was told no, because each outlet in the garage had to be GFCI, and the common neutral would constantly trip the GFCI. Had to run separate romex for each circuit. It can get confusing when inspectors interpret the code differently.</snip>

[Von Bickley]

Doyle,
In my present shop and in my new shop that is under construction, all my wiring is #12. I wouldn't think about running #10. In my opinion, that is over kill.

PS: Certified electrician since 1971...

[Gary Sostrin]

As long as the quoted current requirements for the equipment include any inrush current then you are ok. If it is for steady state only then you might want to find out the max draw. I was wondering, if the labor is almost the same for laying the wire, how much is the cost differential of the 10 gauge wire vs the 12 based over a 10 year usage. My 2 cents.

[Doyle Alley]

As long as the quoted current requirements for the equipment include any inrush current then you are ok. If it is for steady state only then you might want to find out the max draw. I was wondering, if the labor is almost the same for laying the wire, how much is the cost differential of the 10 gauge wire vs the 12 based over a 10 year usage. My 2 cents.

Labor is free (me). The cost of 10 would be higher but I don't know how much. The killer is the thickness of the wire itself. Have you ever tried wiring 10ga? 12ga is as big a pain as I want to deal with when trying to connect it to outlet terminals.

[Joe Jensen]

Doyle,
I've done a ton of my own wiring for the shop. I didn't plan for enough expanision and as a result I now have to do some significant rewiring.
1) Put in a large enough sub panel to have room for expansion.
2) Use the 10 gauge wire. You never know when you will need higher amperage. I just upgraded my table saw from a 3HP to a 5HP. Fortunately I wired with 10 guage wire. Now I just need to put a larger breaker in.
3) Use commercial grade recepticles. They wire much easier with the large guage wire and they last longer.

[Russ Filtz]

Why NOT run 12/3 for your 120 circuits? To me it's required, unless you have planned on a separate ground wire. The 12/3 would also work for the 240v with the white coded for hot with marker or tape. The extra wire there would also be used as a ground.

For the same HP, 240 runs HALF the current down each hot leg, so thinner gauge can actually be used. Until you get to some beefy motors, you may not need 10 AWG, but it still might be good to use esp. if you will have several motors on one circuit.

I was checking on a well pump recently (fairly small 1 HP) and the wire gauge for 110 went from 12 to 10 to 8, etc. every 50-100 feet run. For the 240 wiring, it stayed at 14 until about 400 feet or so (240 went to 12, but the 110 was at 6!)

[Rob Beckers]

Hi Doyle,

Here's yet another variation on the same theme: I'm planning to run 12/3 to power both a mix of 120 and 240V outlets. One end of the cable goes to a double pole breaker (so I have two 120V phases, and neutral on the third wire), then along the cable I'll wire up 120V outlets between one of the phases and neutral (alternating the phase between outlets so the load gets divided), and use both phases to wire up 240V outlets. The plan is to have about twice as many 120V outlets as 240V outlets, in 4x4" boxes with two dual-outlets for 120V and 240V outlets, and one dual-outlet for only 120V outlets (every other box). Those 4x4 boxes are large enough to be up to code in terms of "fill factor" if 2 1/8" deep ones are used. All the wiring is metal-clad, it'll be run along the baseboard.

For safety I'll put in a GFCI, in this case since it's a mixed load on two phases and neutral I need a special one: I'm using a Leviton 8895-00E together with a 3-pole contactor.

I just got all the supplies I need in. Now the wait is for a spare weekend to wire it all up.

-Rob-

[Ken Garlock]

Ken,
I wanted to do something similar and was told no, because each outlet in the garage had to be GFCI, and the common neutral would constantly trip the GFCI. Had to run separate romex for each circuit. It can get confusing when inspectors interpret the code differently.</snip>

Charlie, I got caught up in the GFCI stuff also. The inspector said that because I had a double (french) door in the shop, he 'liked to see' GFCI outlets. What a bunch of bull stuff. Sooo, I our electric an had to install 8 pair of duplex outlets in order to pass. I didn't want the GFCI in the first place. In the shop I consider them to be for little old ladies and others of limited abilities. Oh well, some times you just have to say 'where and how high' to get things done. It was a good thing I didn't meet up with the inspector, otherwise I would have let him up the green tag on the meter, and then asked for written documentation regarding the need for them when the nearest source of water was over 50 ft away.
Grrrrr.:mad:

And yes, a garage must be GFCI protected. I guess it is because of the potential for having water on the floor thus providing a good electrical ground.

[Kent Fitzgerald]

Why NOT run 12/3 for your 120 circuits? To me it's required, unless you have planned on a separate ground wire.

Not necessary. NM #12-2 WG (commonly known just as 12-2), includes a ground wire in addition to the two current-carrying conductors.