Using neutral as ground

[seagull369]

I just wanted to double check with you guys before doing this.... I bought a 240V compressor which has a plug similar to the one shown in the pic on the left. The outlet I want to use for it in my garage has the style to the right.

The plug on the left, it seems, has a ground on top and either parallel pins are the hot leads. I'm pretty sure the receptacle on the right has 2 hots again but one of those (maybe the bottom one) is for neutral.

My question is, would it be all right it I swapped the plug on the compressor to match what I have in the garage and make make the ground on the compressor end go into the neutral line? That 240v outlet goes directly into the breaker and no other outlets in the circuit

 

[ddawg16]

When you say left, do you mean my left or your left?

Ok, lets do it this way.

The male plug on my left is a typical 15A 120Vac plug.

The female receptacle on my right is your typical 240Vac (10-20R?) receptacle. It will not have a neutral, just 2 120Vac (= 240Vac) lines with a ground.

I would look at your compressor motor and see if it can be wired for 240Vac.

Otherwise, just go find a standard recpt in your garage and use that.

 

[wyliesdiesels]

I just wanted to double check with you guys before doing this.... I bought a 240V compressor which has a plug similar to the one shown in the pic on the left. The outlet I want to use for it in my garage has the style to the right.

The plug on the left, it seems, has a ground on top and either parallel pins are the hot leads. I'm pretty sure the receptacle on the right has 2 hots again but one of those (maybe the bottom one) is for neutral.

My question is, would it be all right it I swapped the plug on the compressor to match what I have in the garage and make make the ground on the compressor end go into the neutral line? That 240v outlet goes directly into the breaker and no other outlets in the circuit

It would be easier if you had the NEMA numbers on the outlet and plug.

But no thats not a good idea.

What is the HP rating on the motor?

Is the outlet in your garage near the washer hookups?

 

[wyliesdiesels]

When you say left, do you mean my left or your left?

Ok, lets do it this way.

The male plug on my left is a typical 15A 120Vac plug.

The female receptacle on my right is your typical 240Vac (10-20R?) receptacle. It will not have a neutral, just 2 120Vac (= 240Vac) lines with a ground.

I would look at your compressor motor and see if it can be wired for 240Vac.

Otherwise, just go find a standard recpt in your garage and use that.

cant be.

the polarized neutral blade is on the wrong side

EDIT: just noticed you also said a NEMA 10 doesnt have a neutral. Thats also wrong. NEMA 10-** is 2 hots and neutral/ no ground...

Best to look at a nema chart next time.

 

[CGT80]

The plug on the left is 6-50P and is 50 amp 250 volts, no neutral.
It is obviously larger and a different shape than a 5-15P, and it is also what I use for my welders (miller uses this plug with factory ends).

The receptacle on the right is a 10-50R and is listed as 50 amp 125/250 and would have no ground since the ground can not carry power.

You should have been able to open up the receptacle box and check, then check at the panel to see how the circuit was wired (it sounds like you didn't). A multimeter would also tell you more than just looking at the face of the receptacle.

If you don't already know how basic residential electrical is run/used you might search the internet for the info. There is more to learn than what would be posted in a thread like this. If you are not comfortable working in a box or panel, then don't do it. As far as the types of receptacles, I googled a nema chart for receptacles to see how each was designated. Clicking on your picture shows a full size image, and the receptacle has markings. That is assuming you have the same exact receptacle.

Don't assume the receptacle was wired properly or to code. Codes change or vary and it isn't uncommon to see electrical not wired properly.

The code has changed for bonding between ground and neutral and this has come up with sub panels I have dealt with. In the sub panel for my garage, the neutrals and grounds are on the same bus bar, so the wires go to the same place and act the same. For safety, the newer idea is to have a dedicated ground circuit that doesn't normally carry power.

It would be better to use a 6-50 or 14-50, which both have grounds. 14-50 has neutral as well. That is if you can/choose to use a plug and receptacle. I do use the 6-50 for my 5hp compressor. It isn't right, but it works. I suppose it wouldn't be that hard to use a disconnect switch.

To change the receptacle type, you will want to know if you have a ground wire or if there is metal conduit that could be used as a ground, if allowed by code. I don't think code allows using a white insulated wire as ground, but people have wrapped green tape around the white, and used it as a ground. Another option, if in conduit, is to pull the wire and replace with green. Different inspectors will have different requirements for electrical practices as well, so it depends on your goals, anywhere between just making it work and having it signed off by an inspector.

 

[Bert_]

I would just connect the ground from your equipment to the neutral terminal in the 10-50 "crow foot" plug. No need to over complicate this, that wire runs straight back to the panel so the only difference is the color of the wire. I would wager that in my area there are more 10-50's used in shops than 6-50's.

 

[wyliesdiesels]

I would just connect the ground from your equipment to the neutral terminal in the 10-50 "crow foot" plug. No need to over complicate this, that wire runs straight back to the panel so the only difference is the color of the wire. I would wager that in my area there are more 10-50's used in shops than 6-50's.

And how do we know that this circuit is connected to the main service panel and not a subpanel with iso. neutral?

 

[seagull369]

Thanks for all the great replies. The receptacle in my garage is indeed 10-50 and the plug off the compressor is 6-50. Just to answer some of your questions:

- I was present when I had an electrician hook up the garage outlet so I know for a fact it was connected directly to the main box. 2 wires to the double pole and one to neutral. I had it installed to run a Lincoln tombstone welder I have, not for a washer/dryer.

- The compressor is definitely a 240V setup. It's a 60 gallon (over)rated at 6hp.

I don't want to over-complicate things either and I don't really feel like changing the receptacle plug to another style, esp. since I still use my welder once in a while. Considering there's only that one receptacle on that circuit, I think I can treat it as either neutral or as a ground.

 

[wyliesdiesels]

Thanks for all the great replies. The receptacle in my garage is indeed 10-50 and the plug off the compressor is 6-50. Just to answer some of your questions:

- I was present when I had an electrician hook up the garage outlet so I know for a fact it was connected directly to the main box. 2 wires to the double pole and one to neutral. I had it installed to run a Lincoln tombstone welder I have, not for a washer/dryer.

- The compressor is definitely a 240V setup. It's a 60 gallon (over)rated at 6hp.

I don't want to over-complicate things either and I don't really feel like changing the receptacle plug to another style, esp. since I still use my welder once in a while. Considering there's only that one receptacle on that circuit, I think I can treat it as either neutral or as a ground.

Whats the HP or FLA rating on the motor nameplate?

If more than 3HP, it needs to be hardwired to be code compliant..

 

[AngryBeaver]

When you say left, do you mean my left or your left?

Ok, lets do it this way.

The male plug on my left is a typical 15A 120Vac plug.

The female receptacle on my right is your typical 240Vac (10-20R?) receptacle. It will not have a neutral, just 2 120Vac (= 240Vac) lines with a ground.

I would look at your compressor motor and see if it can be wired for 240Vac.

Otherwise, just go find a standard recpt in your garage and use that.

quit posting. everything you just typed is 100% wrong

 

[James-W]

Whats the HP or FLA rating on the motor nameplate?

If more than 3HP then it needs to be hardwired to be code compliant.

Not disagreeing with you, just asking a question. I have a Craftsman compressor that came with a 240 volt power cord already on it. The motor name plate says it is a 4hp motor. Is it because it is an older compressor that a cord is allowed because at the time the compressor was made power cords were allowed for motors of that size? Am I in code violation if I plug the compressor into an electrical outlet?

 

[CGT80]

Thanks for all the great replies. The receptacle in my garage is indeed 10-50 and the plug off the compressor is 6-50. Just to answer some of your questions:

- I was present when I had an electrician hook up the garage outlet so I know for a fact it was connected directly to the main box. 2 wires to the double pole and one to neutral. I had it installed to run a Lincoln tombstone welder I have, not for a washer/dryer.

- The compressor is definitely a 240V setup. It's a 60 gallon (over)rated at 6hp.

I don't want to over-complicate things either and I don't really feel like changing the receptacle plug to another style, esp. since I still use my welder once in a while. Considering there's only that one receptacle on that circuit, I think I can treat it as either neutral or as a ground.

Is the plug on the welder molded and original, or was it added on? I'm not sure why it wouldn't have been a variation with a ground.

If I was going to use the neutral wire as a ground, I would look in the panel and make sure they are bonded and if they are not, I would move that wire to the ground buss and wrap it with green tape. Basically, make sure you have a good/dedicated ground.

 

[TRWham]

Whats the HP or FLA rating on the motor nameplate?

If more than 3HP then it needs to be hardwired to be code compliant..

Can you point me to the Article that states this, please?

 

[teamextreme]

Not disagreeing with you, just asking a question. I have a Craftsman compressor that came with a 240 volt power cord already on it. The motor name plate says it is a 4hp motor.

Did it come with a cord that has the male end on it, or just a cord with a bare end . My 5hp came with a piece of SO cord, but the end was bare, no male cord end.

 

[seagull369]

The compressor is an "oil free" variety Craftsman brand. The motor is hidden inside the plastic housing, and any plates/stickers on the outside just have generic safety info on em. There's is a model number printed but it's mostly worn off (compressor was made in '94) and any sense I could make of it came up with nothing on a Google search. I did find a vid on youtube (

) with one that looks exactly like mine and the the guy on there says his is 240V. I did take apart the 6-50 plug on mine did see white/black/green wires in there. Made me think for a minute it might be 120V but not sure if I can assume that just by the colors.

To answer your question, CGT80, the 10-50 plug on the welder is molded on and is one piece with the cord, so it looks original. It is 30+ years old from the looks of it, so maybe they came that way back then? I did get the welder used, so I guess it's possible someone along the line could have swapped in this style, but if they did they fed it through the back and connected it inside the unit cuz there's no splices on the outside anywhere. I do see your point about why would it need a neutral (120V) for anything.

 

[CGT80]

The 10-50 is probably just what they used back then. I would also guess it is original.

I had a compressor just like that and ended up rebuilding the oil free pump. I remember it being around 15-16 amps and 240v. It is still at my brother's house, as I gave it to him. The compressor that I "upgraded" to, was a sanborn 60 gallon oil lube. It was labeled 5 or 6 hp. It also pulled under 20 amps. In both cases, these are more like 3hp.

No, don't go by the colors on the wires. I have seen the same thing with black and white as the hots and green for ground, on 240 volt machines. If in doubt, go by the label on the outside of the compressor or pop the cover and look at the motor nameplate. They lie about HP, but the voltage is always right unless someone has changed after it left the factory.

I have a real 5hp baldor on the current compressor and it is 28.5 amps, while the newer motors are around 24 amps. Roughly 5 amps per horsepower.

If it was me, I certainly wouldn't bother with a disconnect for that craftsman compressor.

 

[James-W]

Did it come with a cord that has the male end on it, or just a cord with a bare end . My 5hp came with a piece of SO cord, but the end was bare, no male cord end.

It came with a male plug on the end of the cord.

 

[seagull369]

Thanks again for the reply. I wired it up to the 10-50 and it's running fine, thankfully (I wasn't able to test it out when I bought it).

When you said you wouldn't bother with a disconnect, do you mean for the hose or the electric?

'

 

[CGT80]

For the electric, as you are under or right at the 3hp limit for code and even 5hp motors seem to do fine (disregarding code).

That's great that it runs well. Mine was just too dang noisy, and it was outside of the garage.

If you get a chance to pick up a cast iron oil lubed compressor, especially with a 1750 rpm motor and a pump that is below 1000 rpm, it will be a huge difference. I bought a 1947 compressor and restored it just because they are so quiet and built well, but this one will be run every day.

 

[TRWham]

I have never found an explicit limit to cord connected motor sizing in NFPA 70. However, because there is no straight blade NEMA plug and receptacle configuration rated for more than 3 hp (on 208 to 240V), it is a reasonable working limit to satisfy 430.108 and 430.110 if you are not going to use one of the various high capacity switch rated pin and sleeve connectors. Those are common in industrial installations and quite legal at loads way over anything we are going to have in a home shop or garage, but are financial overkill for this problem.

As for the OP's situation, I doubt this compressor exceeds 3 real hp, and the 6 hp is only a marketing rating. You can be sure that the cord on that compressor is fine under UL assuming it is original. I have a vacuum cleaner that claims 6.5 hp right on the side yet runs just fine all day long on a 15 A 120V circuit. A real 6.5 hp would exceed 40 amps on 120V.

I don't know how you wired it, but I would have built a ************* to get from the 6-50 plug to the 10-50 receptacle without modifying either the compressor or outlet. That way there is no confusion later about what receptacle the compressor really needs or what power the receptacle really provides.

 

[wyliesdiesels]

Not disagreeing with you, just asking a question. I have a Craftsman compressor that came with a 240 volt power cord already on it. The motor name plate says it is a 4hp motor. Is it because it is an older compressor that a cord is allowed because at the time the compressor was made power cords were allowed for motors of that size? Am I in code violation if I plug the compressor into an electrical outlet?

The cordage isnt the violation issue if it came from the factory like that.

The code issue has to do with the HP rating on NEMA plugs and outlets.

You would be in violation IF the motor HP is higher than the rating on the plug and outlet youre plugging into.

What does the FLA rating on the nameplate list?

See below about NEMA outlet/plug ratings...

Can you point me to the Article that states this, please?

The code issue with using NEMA plugs and outlets for motors over 3HP is a listing violation.

NEMA plugs and outlets arent rated for more than about 3HP.

This mainly has to do with using the plug as a disconnect and the resultant arc while unplugging it when running.

 

[seagull369]

That's great that it runs well. Mine was just too dang noisy,

Man, you're not kidding... I was wearing hearing protection earmuffs before I even threw the switch and it was still too loud.

I do have a nice made in usa oil lube-cast iron compressor but it's only a 20gal. It is quiet and I like it a lot, but it can be a bear to start in the colder weather =(