Garage 220v Sub

RacerX

RacerX

Professional Knucklehead; aka Jeffncs / RacerX
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Figure I’d throw this out there for the fun of creating a thread…

I ran a 220v/50A circuit o to my garage from the main panel a while back. That circuit terminated at a 6-50R receptacle.

I’m now blessed with a new 220v plasma cutter which will need ship air to run, so I need a second receptacle.

Here’s my plan - swap the current receptacle for a small sub panel housing a single 50A breaker and circuit lugs. I’ll wire in a pair of 6-50R receptacles to the box then power the box with the 6gauge wiring from the main service panel.

I’ll run 10/2 from the sub panel to the the separate receptacles. Each will only see a max of 30A.
 
So you’ll run the compressor off some other circuit? Is the plasma nad compressor combined at 30 amps?
 
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Sounds like it will work. If you want to be belt and suspenders safe, just consult (even an older) NEC on line with regards to wire sizing and OCP device ratings to make sure everything is correct. Remember, tou need to account for deg C rating and can’t just assume a device is 90°C rated unless labeled as such.
 
@Mirac

The existing circuit in on a 50A breaker using stranded 6 gauge wire to the 6-50R.

The new arrangement will use the existing 6 gauge wire into a sub panel housing a second 50A breaker.

Breaker #2 will feed a pair of terminal blocks. Im planning to use dedicated 10/2 wire from the terminal blocks to separate 6-50R receptacles.

Compressor draws 15A.
Plasma draws variable amperage with max of 35A.

It is HIGHLY unlikely that both will be running at the same time.

I have additional 6 gauge wire to use for the receptacles if that’s safer/better.
 
A few concerns....

6-50R is 3 wires. 220 feed should be 4 wires so you have 2 hots, 1 neutral and separate ground.

A 50 Amp 220 volt line is getting 50 Amps on both hot lines so the sub could have 2 30 AMP 120 lines.
 
Perhaps I’m missing a piece here…. But 220v feeding a house from a generator requires 4 separate lines. Ground, common, 2 hot. That’s so you can run 120v off of the 220v input.

As pictured below (and, again, I could be wrong…). These are all 220v 6-50R 50A plugs/receptacles. 3 prongs for the ground and 2 hots.

If I wanted 120v to that sub panel, you’re correct in stating that I need 4 lines. This is strictly servicing 3-prong 220v equipment. If any of that equipment had a 120v component, then I’d need a 4th prong.

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Edit to add - I’m having an electrician install a dedicated generator switch and plug for me. That’ll be completely separate and will have 4 prongs.
 
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If at some point down the line I need a common for a 4th prong/common, I’ll easily add it through my conduit and roll with it. I have no need at this point.
 
RacerX said:
I’m going to do some more research and may end up pulling a neutral. If I pull the neutral, I’ll likely end up with a full sub panel.
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The picture you posted looked like a service disconnect and not a sub panel. I’m not a licensed electrician. Worked with my uncle during the summers when I was a teenager. I would at a minimum replace the disconnect with a sub panel.
 
Average Joe said:
The picture you posted looked like a service disconnect and not a sub panel. I’m not a licensed electrician. Worked with my uncle during the summers when I was a teenager. I would at a minimum replace the disconnect with a sub panel.
Click to expand...
I pulled that post down as I was told it’s something it isn’t. I’m looking at small, surface mount sub-panels now. I’ll have to pull a neutral but that’s not terrible to do…

Probably charge the compressor, swap plugs and burn until I run out of air…. Short-term solution until I have the time to do it right / again.
 
Also… thanks much to all for the advice! Greatly appreciated!,
 
You will need to operate both compressor and plasma cutter simultaneously.

If it were me, I’d pull the neutral and use it along with your existing wiring to provide power to a new sub-panel. Wire the compressor and the plasma cutter to it and go to town.

Based on 15A + 35A max, you should be fine.
 
I don’t think that 50a breaker will hold the compressor and plasma at the same time.
At least not at the inrush with the compressor.

Though I was wrong once... this could be the second time.
 
Will the cutter and compressor cause that 50A GFCI to trip at startup?
 
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Compressor startup is 14A; cutter is 35A at max power, but lower amperage where I’ll be using it.
 
Scsmith42 said:
Jeff, is the compressor CFM output greater than the plasma cutter demands? I know that my plasma cutter requires a lot of air volume.
Click to expand...

The torch calls for 4cfm @ 90psi. That’s well below the output of my 60gal compressor which pushes 11cfm @ 90psi. I’ll burn through some air, but I should be good.

Also - torch runs 20-35A. I’ll likely never need to go above 30A based on my intended usage (18ga sheet metal - 3/16”). The torch is rated to burn through 1/2”…
 
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RacerX said:
@Mirac


It is HIGHLY unlikely that both will be running at the same time.
Click to expand...
Unless all you're doing is small cuts then you're going to be running both at same time. That plasma cutter is going to have a rating for steady air at X CFM at X PSI per second of cutting time. Unless you've got a pretty large holding tank you're going to be popping that compressor on and off the whole time you're cutting as the compressor hits its setting for recharging the tank pressure loss and will run till it's topped off again. I see your numbers in another post and once you've dropped pressure on your tank you're going to need to run your compressor roughly 20 seconds for every minute of cut.
 
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