12-3 Wire size to 30 amp breaker?

I have a detached garage and pulled 12-3 wire (underground) to the garage from a 30 amp circut at the house, to a 30 amp circut in a new box in the garage. I now know I should have run at least 10 gauge wire in the conduit to the 30 amp breaker. I plan to weld 220 from the garage, lights, outlets, perhaps a wall A/C that I'll leave off if I'm welding.....

What risk am I running by not changing to 10 gauge wire or a 20 amp circut? I really don't want to go with a smaller breaker, and it was a VERY DIFFICULT to pull the 12-3 that 40+ feet in the existing 3/4" conduit. Any advice?

 

I'm not an electrician, but I'm afraid that you're right.
You're going to have to pull heavier wire. You shouldn't put 12 on higher than a 20 amp breaker.
Good luck!

 

Sorry, Swingleft. Old Guy's right. The NEC prohibits use of an overcurrent device exceeding 20 amps with #12 wire. I know that's not what you wanted to hear, but the NEC sets this limit because #12 wire will overheat if you make it carry more than 20 amps. This is generally what causes house fires attributed to the electrical system failure. The rule is Max. 15 amp breaker for #14 wire, 20 amps max for #12, and 30 amps for #10. No two ways about it. Of course you may use a breaker of LESS than the max allowed, but not GREATER than.

You may be kicking yourself now, but if you go to the trouble to pull the #10 wire you'll be glad you did later, and you can have closure.

Juice

 

I may have good news for you, then again I may not.

Check your welder. If this welder is a wire feed welder it may only call for a 20 amp circuit feeding that welder. Also check you A/C unit, it too may only call for a 20 amp circuit. If this is true. You may be able to get by with reducing that breaker protecting that 12 awg feeder to a 20 amp breaker and still do what you want and have the required protection for that 20 amp feeder. The hold back would be an either welder or A/C unit not both situation. Check you ratings on your welder and A/C before you do anything. If you have a stick style arc welder it may call for a 60 amp minimum circuit supplying that welder. All depends on what welder and how big of an A/C unit you have and whether you want to put up with minimum wire size causing the 20 amp breaker to kick if you overload it. Do not leave a 30 amp breaker on that 20 amp rated wire.

Hope this helps

Wg

 

Hey guys (OldGuy, JuiceHead, and especially Wgoodrich)

I just wanted to thank you for your advice.
I read your notes this morning, then went to Home-Depot. I spent $50 and busted up a small hole in the concrete to access a 90-degree bend in the conduit (the last guy did it WAY wrong). Long story short: I RE-PULLED 10 gauge wire~!! I ate it on the time and money I spent pulling the 12-3, but I know I'll be happier in the long run. I checked into the amps of my welder and A/C...I probably would have been OK to just put a 20amp breaker on there (yes, it it a wire feed welder). You motivated me to do it right...Thanks!

Tom Norton
SwingLeft

 

Tom,
The other issue that wasn't mentioned is that if your garage was not wired properly (NEC), and an electrical fire burned it and anything else around it, your fire insurance company wouldn't have to pay you a cent.
Glad you took wg's and juice's advice...those guys are the pros here.
Good Luck!
Mike

 

To open an old argument I will advise you that you need to drive a ground rod at your garage and attach it to the Equipment Grounding Conductor in your feeder cable. If you used individual conductors I hope you pulled a bare or green wire with the other three. If you did not please check back with us here or write to me directly.

 

I sure did pull the green one. I knew about the ground rod.... but I was considering ingnoring that one little detail. Doesn't it have to be Eight feet deep? And what diameter? I will probably stick SOMETHING in the ground, as I really don't want any problems out there.

~Tom