quick electrical question

[Russ Ambrose]

getting ready to wire the new shop and have a quick (hopefully) question. i understand that 10-3 wire is generally used to facilitate a 30 amp circuit, but is there any reason (code or safety) that i couldn't run 10-3 wire but instead use a 20 amp breaker and 20 amp plug? i only need 20 amp circuits for my current equipment, but would like to (if possible) run 10-3 in case i later get equipment that requires a 30 amp circuit (at which point i would replace the breaker and plug accordingly). thanks.

[Mike Hollingsworth]

No Problem

[Mike Henderson]

I agree - no problem. Except that 10 gauge wire is a bit hard to handle (bend, stuff back into a box, etc.).

Mike

[Phil Thien]

The only possible issue is that you should make sure your receptacles and plugs are designed to accommodate 10. If those items state a maximum wire size of 12, then you shouldn't use 10. I've always wondered whether it would be okay to pigtail off a 10 to some 12 in order to connect to receptacle (for example). I've been told doing so would be a gray area.

[Mike Heidrick]

10-3 romex is 3 conductors and a ground. You only need 10-2 for a 240v 1phase - two conductors for hots and a ground. Some guys use 10-3 if they want to use the same run for 120V too as the 3rd conductor is used as the neutral.

[Rollie Meyers]

10-3 romex is 3 conductors and a ground. You only need 10-2 for a 240v 1phase - two conductors for hots and a ground. Some guys use 10-3 if they want to use the same run for 120V too as the 3rd conductor is used as the neutral.

You cannot tap a 15 or 20A receptacle or circuit off a 30A circuit, some type of overcurrent protection is required...

[Mike Heidrick]

You cannot tap a 15 or 20A receptacle or circuit off a 30A circuit, some type of overcurrent protection is required...

I am not a fan of using 10-3 for anything other than 3 phase lines. Personally I run all seperate 240V and 120V lines.

It may not be code or recommended/safe but you can do it and the tools will work perfectly.

[Rollie Meyers]

I am not a fan of using 10-3 for anything other than 3 phase lines. Personally I run all seperate 240V and 120V lines.

It may not be code or recommended/safe but you can do it and the tools will work perfectly.

And it unwise to do non code compliant or unsafe work, it works to replace fuses with copper pipe but is not prudent to do so, just because one can, does not mean they should.

[Steve Meliza]

is there any reason (code or safety) that i couldn't run 10-3 wire but instead use a 20 amp breaker and 20 amp plug? i only need 20 amp circuits for my current equipmentThere is no code or safety reason why you can't use #10 wire as you describe.

The purpose of the breaker per NEC definition is to protect the wire from over current. The ampacity rating of wire is its maximum, there is no minimum rating. I do agree that you must make sure to use outlets rated for #10 wire connections or pigtail with #12. You'll just need to remove or replace those pigtails if you ever up the circuit to 30A.

The breakers and outlets are required by NEC to have the same rating except when you have a 20A breaker you can use 15A or 20A rated outlets.

[Prashun Patel]

As said, 10-3 will be harder to handle than 12-3 or 12-2.

If you ever upgrade, it will likely be to handle 220v tools. In this case, the current draw will actually be less than 110v for the same amount of power. 12-2 will be plenty for a 20A 220v circuit to handle a single power tool at a time.

[Chris Padilla]

I ran #10 throughout my garage but I ran it in conduit and used STRANDED #10. I didn't feel like buying separate spools and colors of #10 and #12 so it was all #10. Now this was a good 7-8 years ago when copper was a lot cheaper.

[Kent A Bathurst]

Oversize the wire, with respect to the breaker, is OK.

The breaker keeps the wire from meltdown.

Then, as you say, you can ^^ breaker to 30a in the future if you want. All good.

Going the other way is verboten - ie, oversize the breaker for the wire guage. A 30a breaker on 20a wire is how houses burn down.

[Anthony Whitesell]

You cannot tap a 15 or 20A receptacle or circuit off a 30A circuit, some type of overcurrent protection is required...

True. As the OP states, he would like to put in 20A breaker, 10g wire and 20A outlets. That would be fine. The gotcha will come when the 20A breaker is changed to a 30A breaker, then all the outlets will need to be upgraded as well. Which will very likely make the original outlets useless as 15/20A outlets are very different in the plug configuration from the 30A outlets.

[Rod Sheridan]

getting ready to wire the new shop and have a quick (hopefully) question. i understand that 10-3 wire is generally used to facilitate a 30 amp circuit, but is there any reason (code or safety) that i couldn't run 10-3 wire but instead use a 20 amp breaker and 20 amp plug? i only need 20 amp circuits for my current equipment, but would like to (if possible) run 10-3 in case i later get equipment that requires a 30 amp circuit (at which point i would replace the breaker and plug accordingly). thanks.

The other option is to buy machinery with better quality motors.

A high efficiency, high power factor motor will not require as large a feeder.

Now, that's a somewhat tongue in cheek answer, however it's factual.

A good 3 hp motor will run from a 15 ampere circuit at 240 volts, a 20 ampere circuit will be plenty large enough for a home shop.

A 20 ampere multi-wire branch circuit will runn all your 240 volt and 120 volt machines with one breaker and one feeder............Rod.

[Rollie Meyers]

I ran #10 throughout my garage but I ran it in conduit and used STRANDED #10. I didn't feel like buying separate spools and colors of #10 and #12 so it was all #10. Now this was a good 7-8 years ago when copper was a lot cheaper.

If you needed green or white colors, you violated code by remarking them, 6 AWG and smaller is not allowed to be re-identified as grounding, or grounded (neutral) conductors. See 250.119(A), & 200.6(A)

[Steve Meliza]

If you needed green or white colors, you violated code by remarking them, 6 AWG and smaller is not allowed to be re-identified as grounding, or grounded (neutral) conductors. See 250.119(A), & 200.6(A)

He's not saying that he only bought one spool of #10. My read on this is that he didn't want a green spool in two sizes, a black spool in two sizes, and a white spool in two sizes so he went with all #10 to cut the spool count in half.

Besides, he could have bought one spool of #10 white and still wired everything to code with a little extra effort. And if he didn't want to strip the white insulation off to make bare wire for the ground he could have used EMT for his conduit and skipped the ground wire altogether!

[Chris Padilla]

I bought a spool each of #10 stranded in black, white, red, and green and wired the appropriate colors. My understanding, however, is that the green wire (ground) could have been sized smaller? True or not?

[Steve Meliza]

Copper #12 is good for up to 20A ground but #10 will do through 60A ground, so you still needed the #10 ground to realize the full 30A capability of the current carrying conductors.

[Kevin Goss]

Short answer, yes you can, however 10-3 is expensive so be sure you need it. If you just need 20a 240v you could just use 12-2 and will cost 1/3 to 1/2 as much for the wire. Run the 10-3 when you NEED it. You may never need it. Where im from 50' of 10-3 is $75. You could get 250' of 12-2 for that price. 10 awg is perfectly fine for 20a applications. In industrial situations its used all the time to account for long runs with voltage drop. But like other posters said you could use the nuetral for 120v or for future 3 phase machines. Good luck with your project!

[Jason Roehl]

Copper #12 is good for up to 20A ground but #10 will do through 60A ground, so you still needed the #10 ground to realize the full 30A capability of the current carrying conductors.

Take a gander at 12-2 or 10-2 Romex sometime. The ground wire is smaller--it's not 12-AWG or 10-AWG like the current-carrying conductors, respectively.

[Steve Meliza]

Take a gander at 12-2 or 10-2 Romex sometime. The ground wire is smaller--it's not 12-AWG or 10-AWG like the current-carrying conductors, respectively.

The stuff from the 50's and maybe into the 60's has a smaller ground wire, sure. I assumed he was buying modern wire similar to Romex and conforming to these specifications: http://www.southwire.com/ProductCatalog/XTEInterfaceServlet?contentKey=prodcatsheet6

[Rollie Meyers]

He's not saying that he only bought one spool of #10. My read on this is that he didn't want a green spool in two sizes, a black spool in two sizes, and a white spool in two sizes so he went with all #10 to cut the spool count in half.

Besides, he could have bought one spool of #10 white and still wired everything to code with a little extra effort. And if he didn't want to strip the white insulation off to make bare wire for the ground he could have used EMT for his conduit and skipped the ground wire altogether!


You cannot reidentify a white conductor in a conduit, ever. This is only permitted when they are part of a cable assembly such as NM, or MC, Metal Clad cable. When using a metallic conduit for grounding it eliminates the need to oversize the grounding conductor when the ungrounded conductors are oversized such as using 10 AWG for 20A circuits, see 250.122(B). Many NEC editions ago it was only required to increase the grounding conductor when the ungrounded were increased in size for voltage drop, that exception was dropped in later code cycles, now it has to be done whenever the ungrounded conductor size is increased, even if it was done because it was all that was on the truck.

[Anthony Whitesell]

You cannot reidentify a white conductor in a conduit, ever. This is only permitted when they are part of a cable assembly such as NM, or MC, Metal Clad cable.

That's news to me. I see professional electricians in commercial and industrial applications, re-color-coding black, white, and blue conductors (all not part of a pre-fab cable like NM) constantly. ie. they use lots of colored electrical tape. I did take exception to the instance where the recolored blue to black and black to white, I asked they change the blue to white and leave the black alone.

[Rollie Meyers]

That's news to me. I see professional electricians in commercial and industrial applications, re-color-coding black, white, and blue conductors (all not part of a pre-fab cable like NM) constantly. ie. they use lots of colored electrical tape. I did take exception to the instance where the recolored blue to black and black to white, I asked they change the blue to white and leave the black alone.

You cannot reidentify a WHITE conductor 6 AWG or smaller, and cannot reidentify a green EVER, other then that are no issues, other then no phase tape on 6 AWG & smaller to make it a grounding conductor, it is common to remark a 6 AWG black w/ green tape but it is a code violation, I cannot bring myself to do it but it's not unsafe just a violation.

[Chris Friesen]

You cannot reidentify a WHITE conductor 6 AWG or smaller

Sure you can. 200.7(C)(1) allows you to reidentify a white conductor of 50V or more for use as an ungrounded conductor.

[Phil Thien]

Sure you can. 200.7(C)(1) allows you to reidentify a white conductor of 50V or more for use as an ungrounded conductor.

I think his previous post made clear he was speaking of wire inside a raceway, and he is correct.

[Anthony Whitesell]

Better yet, it is required (to the best of my knowledge) the white conductor of 14/2, 12/2, and the like of NM cable to be taped black when used in 220V application to indicate that it is a hot conductor and not a neutral.

[Rollie Meyers]

Take a gander at 12-2 or 10-2 Romex sometime. The ground wire is smaller--it's not 12-AWG or 10-AWG like the current-carrying conductors, respectively.

This is not the case w/ cables since the 1971 NEC was released prior to that the grounding conductor was 16 AWG for 12 & 14 AWG NM cable, since then the grounding conductor is the same size for as the grounded (neut.), & ungrounded (hot) conductors in 10, 12, & 14 AWG cables.