230V Compressor wiring/outlet

[monteperformance]

I've done many searches and read a lot on this but I'm still a bit unsure if I am wiring up my new compressor correctly.

It's a Husky 60gal 230 volt, 3.7 HP motor, listed at 15 amps. I have a sub panel in my garage about 18 feet from the compressor. I already had a dedicated 20 amp circuit for my old 120v compressor with an outlet right next to it.

The existing wire to the outlet is 12-3 romex. So I plan to swap the breaker for a 20 amp 230v, and the receptacle for a 6-20r, and wire up a 6-20p plug on 12-3 power tool cord to the compressor.

I know the red and black leads in the romex will be the 2 hot leads. The part I am unclear on is do I use the white (neutral) that is there already, or just hook the round (center) hole to the ground wire that runs back to the sub panel?

Am I correct in using the 6-20p plug and outlet?

 

[awdblazer]

just cut the white wire off

 

[Highbeam]

You will abandon the white wire but be sure that the chosen 6-20r is a 240 volt plug. If that plug is conventionally a 120 volt plug then some yahoo might plug a 20 amp 120 volt device into it and cook it.

 

[justsam]

The existing wire to the outlet is 12-3 romex.
QUOTE]

How is this "existing" outlet wired? Assuming it is a duplex outlet, is it split, i.e. red lead on one brass screw and black lead on the other brass screw, and the link between the two outlets open? Or is the red lead just not used? Are there two breakers for this outlet?

You mention an adjacent socket. Is it fed from this romex? Do you still have a need for this adjacent outlet to provide 120 VAC?

 

[great white tj]

You will abandon the white wire but be sure that the chosen 6-20r is a 240 volt plug. If that plug is conventionally a 120 volt plug then some yahoo might plug a 20 amp 120 volt device into it and cook it.

I would just wire it up and use a 230volt plug, I just don't understsnd why someone sees the need to change the plug on a 230volt tool ect..Some Ding Dong will come along and try to us a 120volt tool in that plug...

 

[monteperformance]

The existing wire to the outlet is 12-3 romex.
QUOTE]

How is this "existing" outlet wired? Assuming it is a duplex outlet, is it split, i.e. red lead on one brass screw and black lead on the other brass screw, and the link between the two outlets open? Or is the red lead just not used? Are there two breakers for this outlet?

You mention an adjacent socket. Is it fed from this romex? Do you still have a need for this adjacent outlet to provide 120 VAC?

The existing outlet box has 2 receptacles, each one has it's own breaker. One outlet was for the old 120v compressor, and the other for general use. The romex 12-3 feeds both of these outlets. I would like to still retain the one for general use, but I assume will have to run a new wire for that.

 

[monteperformance]

I would just wire it up and use a 230volt plug, I just don't understsnd why someone sees the need to change the plug on a 230volt tool ect..Some Ding Dong will come along and try to us a 120volt tool in that plug...

The compressor did not come with any cord. That is why I was going to use the 6-20p plug (250 volt/20 amp). That way nobody will be able to plug in any 120 volt device.

 

[justsam]

The existing outlet box has 2 receptacles, each one has it's own breaker. One outlet was for the old 120v compressor, and the other for general use. The romex 12-3 feeds both of these outlets. I would like to still retain the one for general use, but I assume will have to run a new wire for that.

Great that explains the original use of the 12/3.

Electrical theory wise you have all you need to provide both the 240 VAC and the 120 VAC, however I suspect there is no way to do it within code and I will leave that answer up to the professionals on this board.

If it is easy enough to run a new Romex you may want to make a new run just for the compressor, which I would do with 10/2 to give a little more margin on that 17 Amp compressor. You could keep your two 120 VAC outlets on different circuits. This would require an additional breaker set for the 240 VAC.

 

[Falcon67]

I would take the 240 (red+black) up to your 240V socket and use one side of your 12-3 (black+ neutral, or red+ neutral) to feed a regular 120V convenience outlet. I personally used a twist lock for my compressor. The outlet is close to the compressor head and I didn't want the plug to vibrate out. The cord I used for the compressor was some left over 12-3 and as above I just cut the neutral off. But you can use 12-2 and just use a marker to color the white lead.

 

[monteperformance]

I would take the 240 (red+black) up to your 240V socket and use one side of your 12-3 (black+ neutral, or red+ neutral) to feed a regular 120V convenience outlet. I personally used a twist lock for my compressor. The outlet is close to the compressor head and I didn't want the plug to vibrate out. The cord I used for the compressor was some left over 12-3 and as above I just cut the neutral off. But you can use 12-2 and just use a marker to color the white lead.

This sounds a lot easier. I do remember reading about how a sub panel doesn't have the ground bonded to the neutral, so I just wanted to make sure I'm okay just using the 2 hot legs and the ground (green) for the compressor outlet.

Thanks.

 

[justsam]

I would take the 240 (red+black) up to your 240V socket and use one side of your 12-3 (black+ neutral, or red+ neutral) to feed a regular 120V convenience outlet. QUOTE]

This is what I was alluding to in terms what was possible electrically, but I am not sure of code. You may even go so far as to split your 120VAC outlet and feed one with red/neutral and the other with black /neutral. Certainly using both 120VAC and 240VAC is done inside appliances such as electric ranges, but I am not sure if it is OK to do inside a J-box, much like a Multi Wire Branch Circuit.

In your particular case with a 17 Amp load when compressor is running, you have a max 3 Amp draw from the 120 VAC outlet.

 

[theoldwizard1]

The existing outlet box has 2 receptacles, each one has it's own breaker. One outlet was for the old 120v compressor, and the other for general use. The romex 12-3 feeds both of these outlets.

No need to buy a 240V breaker. Most breaker manufacturers sell a kit that will lock 2 handles together, effectively making 2 - 120V breakers that are located side-by-side into 1 - 240V breaker.

I would like to still retain the one for general use, but I assume will have to run a new wire for that.

And a new 120V 20A breaker.

 

[wyliesdiesels]

I've done many searches and read a lot on this but I'm still a bit unsure if I am wiring up my new compressor correctly.

It's a Husky 60gal 230 volt, 3.7 HP motor, listed at 15 amps. I have a sub panel in my garage about 18 feet from the compressor. I already had a dedicated 20 amp circuit for my old 120v compressor with an outlet right next to it.

The existing wire to the outlet is 12-3 romex. So I plan to swap the breaker for a 20 amp 230v, and the receptacle for a 6-20r, and wire up a 6-20p plug on 12-3 power tool cord to the compressor.

I know the red and black leads in the romex will be the 2 hot leads. The part I am unclear on is do I use the white (neutral) that is there already, or just hook the round (center) hole to the ground wire that runs back to the sub panel?

Am I correct in using the 6-20p plug and outlet?

Wire for motor circuits is sized at 125% of motor FLC. 3.7hp is not a standard motor size. 3hp is listed at 17a, so using that 17ax125%= 21.25a, which would mean under NEC 2011 code, #12 NM-B wire aka 'Romex', would be a wee bit too small(20a ampacity, 60* c column). Use #10 NM-B or #12 THHN wire, breaker would be sized at max 250% of FLC, or 42.5a which is not a standard size, so roundup to 45a breaker.

I would NOT cut the white wire, but instead leave for possible future use. It wont hurt anything.

Flexible cord is not code approved for use between a disconnect or j box and equipment such as a compressor. Use liquid tight or FMC...

Dont use a 6-20 P + R as its only rated for 2hp!

No need to buy a 240V breaker. Most breaker manufacturers sell a kit that will lock 2 handles together, effectively making 2 - 120V breakers that are located side-by-side into 1 - 240V breaker.......

Incorrect. By code, a 240v circuit is required to be fed by a COMMON TRIP breaker. Just a handle tie on 2 separate breakers next to each other is NOT to code, despite popular misconception and frequent use in that manner. I actually see it done all the time but no one wants to pay to swap breakers.

Handle ties on non common trip breakers are used for MWBC....

 

[Highbeam]

Incorrect. By code, a 240v circuit is required to be fed by a COMMON TRIP breaker. Just a handle tie on 2 separate breakers next to each other is NOT to code, despite popular misconception and frequent use in that manner. I actually see it done all the time but no one wants to pay to swap breakers.

Handle ties on non common trip breakers are used for MWBC....

Plus, it's hokey. The proper 240 breaker is like 7$ and it will look like you meant to do it this way instead of a hack. You'll spend 7$ trying to buy and install that tie bar.

 

[DirtRoad]

I have the same compressor.

I just used 12-2 and wired it right to the compressor. I dont see the need to put a cord on it and install a plug.

 

[monteperformance]

The motor was listed as 15 amps on the HD website but I looked in the manual and it is saying 13.5 amps. I don't want to do this wrong but I also don't want to start spending a lot of money on wiring upgrades if I don't need to.

I got the idea of using the power cord on this forum from other people with a similar setup. It's just so I can move the compressor easily if I need to. But now it is sounding like I'll be better off just hardwiring it to save the trouble of setting this up right.

I attached the specs from the manual. If it's really 13.5 amps then at 125% I would be at 16.875. It also says minimum branch circuit 20A. Or is the manual giving me bad information?

 

[DirtRoad]

Just use 12-2, run the wire right to it, no cord and all that mess.

Trust me, you wont be moving it often, if ever. Decide where you want it permanently and just put it there, be done with it.

 

[wyliesdiesels]

The motor was listed as 15 amps on the HD website but I looked in the manual and it is saying 13.5 amps. I don't want to do this wrong but I also don't want to start spending a lot of money on wiring upgrades if I don't need to.

I got the idea of using the power cord on this forum from other people with a similar setup. It's just so I can move the compressor easily if I need to. But now it is sounding like I'll be better off just hardwiring it to save the trouble of setting this up right.

I attached the specs from the manual. If it's really 13.5 amps then at 125% I would be at 16.875. It also says minimum branch circuit 20A. Or is the manual giving me bad information?

By code, u dont use the nameplate amps but instead check the horsepower rating and look up the NEC listed FLC for that HP. Read comment # 13....

Having said that, I think u would probably be fine on a 20a dedicated circuit and thats also what the manufacturer suggests!

 

[monteperformance]

By code, u dont use the nameplate amps but instead check the horsepower rating and look up the NEC listed FLC for that HP. Read comment # 13....

Having said that, I think u would probably be fine on a 20a dedicated circuit and thats also what the manufacturer suggests!

Got it. Thanks for the info.

 

[monteperformance]

I ended up hardwiring it on the 20 amp dedicated circuit with a new double breaker with 12-2 and it's running great. Thanks for the help.

 

[Falcon67]

Thanks for the update - glad to hear it's up and running!