I'd like this to be answered by a real electrician

My idiot ex-buddy (who is suppose to be an electrician, ex-buddy mostly because he became a miserable drunk) wired up my 5hp compressor 230v with 12 gauge 20amp breaker. It ran fine for years but has started to trip the breaker.
The motor is 5hp, 1740rpm, single phase, 208/230v and 24.5 amp. Fresh rebuilt, new bearings, run cap and switch.
My research says it should be 30amp using 10awg wire. It's about a 50' total run.

Now, I have all kinds of 12awg T-90 wire and conduit running almost all the way to the compressor and then I have a long enough piece of 10awg BX to get me the rest of the way. I know how to twist a proper joint.

Is it OK/legal to double up the 12awg T-90 to make 10awg?


The exact same motor is in the vid below, showing the spec plate at 1:54

https://www.youtube.com/watch?v=4RRB7tvm-eU

I'm not a licensed electrician but I'm sure it would not be to code. One reason is if there was a fault on one of your conductors then the remaining conductor would be handling the full load.

Yes/no.

It's not to code. to run wires in parallel they must be #1 or larger.

Will it work, yes. It would slightly exceed the #10 capacity.

Thanks Mike...damn mo'money I'd rather stick to legal.

Could you look at the rating plate? Am I right that it should be 30amp circuit for this motor?

Needs to be rated for the FLA full load amperage. #12 THHN is now considered by the NEC as good for 30A but most EE's only use it up to 20A. If your circuit is dedicated, the 12 might work. I'm not sure what T90 wire is rated for.

What I'm seeing is the amp rating is the same on THHN and T-90, but the coverings are different, so some can be used in wet locations while T-90 can't be. T-90 I have is is rated at 75C
http://www.southwire.com/products/THHNTHWNTWN75T90OEM.htm

This blog is from some kind of Electricians school, A mod starts the discussion and on the last page he says yes to a #12 THHN circuit on 30amps.
http://forums.mikeholt.com/showthread.php?t=62102&page=6

That means when the insulation gets above 75C it will start to fail, melt, short out. THHN is rated at 90C and is the most common used today.

It should be fine as long as it's not continuous load and gets hot. The motor will use the most amperage at start up and then taper down. You should be fine but your breaker or fuse should be rated 125% of the load minimum.

Slightly left of field approach.
I have a 15cfm compressor at home and it will normally run fine. Cold mornings or extra load on our line it struggles to start and pops the breaker.
I don't really need the total capacity of the compressor so I went a fraction smaller on the motor pulley and haven't had a problem since.
The pulley was free and heck of a lot easier than a better motor than the Chinese thing on it.

Just found a 55' chunk of 10/3 BX in my stash. might be a bit short to do a sanitary install, but long enough to get me by till I can run the EMT (then cable w/strain relief) right to the compressor.
This is how I wired my 2 post lift, so 2/3 of the way the EMT is already done.

Well I ran the #10 BX plus a 30amp breaker and it ran perfect to 160lbs without popping the breaker, woo-hoo!
The run is a hack, up over the lights, but good enough for getting the job at hand done. Putting on a steel roof and I bought a framing nailer for the strapping.
In the winter I'll square it away right.

For the life of me I don't know why my buddy, the union electrician, would run it on #12 with piss poor grounding. At the time I just bought what he told me, I wasn't cheaping out on the materials. It also worked that way for 15 years, but I bought a new compressor head with a bigger draw/faster recovery time.

Thanks Mike for your help.

Start amps and running amps are different, starting amps are more.
Tag on motor will show both , typically 30/15 or something in that format.

Like a starter on our cars, as these motors get older and brushes get more worn, the starting amps go higher.

Not an electrician, but someone who has dealt with this issue for many years.

Also, if you got a larger head unit, the starting amps went up again to get the unit moving.
It may have worked fine when the motor was new and over time it finally started to pull more of a load than the breaker could handle.