Motor Branch with Receptacle

[dellphinus]

Guy wants to install a fixed compressor on a dedicated circuit, but with a cord and plug/receptacle. Unit's instructions say to permanently wire, but he wants it "pluggable" so he can move it if necessary. For now, neglect the "not in accordance with the instructions" ...

430 calls out sizing for conductors and CB, and states a HP rated receptacle must be used. I contend that is what should be done.

Others have suggested that the motor sizing rules don't apply if you put a plug/receptacle on the branch, and you must size the wires/CB to the receptacle.

I can find no references to anything that indicates you can't size per 430 if you use a plug/receptacle.

Best answer, because of future homeowners, is probably to pick a receptacle to handle the motor, then size it all as a general purpose circuit?

 

[bphgravity]

Re: Motor Branch with Receptacle

For custom jobs like this, Article 430 is the better place to make claculations. Basically, size the branch-circuit OCD to Table 430.52, the branch-circuit wiring to 430.22. The receptacle and the cord-plug attachment will have to be sized according to the OCD rating.

 

[paul]

Re: Motor Branch with Receptacle

This Post went over the question you're asking.

Goodluck

 

[dellphinus]

Re: Motor Branch with Receptacle

Originally posted by paul:
This Post went over the question you're asking.

Goodluck

Not really...

That thread didn't address the potential for the motor rated branch circuit to be used for a non-motor load some time down the road, due to the receptacle (and my original question didn't ask it very well either). I know you can't idiot-proof everything, but it seems like a valid concern. This guy moves, takes his compressor with him, now there's a 50 amp/220v volt recpetacle wired with 12 gage wire sitting there, just waiting...

 

[paul]

Re: Motor Branch with Receptacle

I wouldn't wire it with a higher rated breaker, if that's what you're talking about. The link I posted tells about the horsepower ratings of the receptacles. However, the code does allow us to put larger breakers, or fuses on a motor for the inrush current, but only with the proper OL's installed. If you do this with a receptacle, then I would think you are in violation of the code. Most compressors have built in overloads, so you don't have to worry about the over current protection.

If you have a 50 amp recept. wired with 12 AWG on a 20 amp breaker, there is no violation. The breaker will trip long before you get to 50 Amps. If you place a 50 Amp breaker on it, then you're out of compliance for obvious reasons. I have a problem putting a larger motor, something other than a DW or GD, on a recept. If the homeowner insists, tell him 'no.' Or ask him if he's got good fire insurance. Personally, I think you're sticking your neck way out by trying to accommodate him on his request.

Goodluck

 

[dellphinus]

Re: Motor Branch with Receptacle

Paul,

I agree, and I'm not sticking my neck out, I wouldn't do it.

But the question remains, is it a violation of code to wire a motor circuit with a receptacle? ANswer so far is no, per 430.109. So we have a circuit sized and rated for a large motor, say 50 amp breaker, 12 gage wire 50 amp receptacle. Now the guy moves and takes his compressor. Circuit that remains is safe and compliant for a motor, but nothing else, and next owner has no clue unless he's an electrician.

IMO, only way to make that condition safe is to up the wire to the breaker size, but it is not required by code, as best I can tell.


BTW, this is from a homeowner question in another forum, 7 HP (marketing HP) compressor, 230 V 15 Amp stationary unit, instructions say to hardwire, he wants it cord and plug.

 

[paul]

Re: Motor Branch with Receptacle

I say, wire it up. Put it on a 20 amp outlet and a 20 amp Zincso breaker. Code compliant and it won't trip.

*Don't try this at home.....Do it at a friends house!