Wiring a 3 prong 220v

[Orangepeel]

I have to wire a cord to an air compressor and I’m probably overthinking it. The cord isn’t colored it’s just a solid gray cord. The instructions list the cord as each outside wire is hot and middle is neutral.
The air compressor has a black hot a white hot and a green ground. I’m a little confused on the center cord wire being a neutral and not a ground? Can it be used the same way? What is the right thing to do in this kind of situation.

 

[Hall]

You're missing a bit of information here.... Are you hard-wiring this ? I wouldn't.... Or is there an outlet involved ? I hope so ! Post pictures of the outlet, the plug, and the "cord".

It's not unusual to go from "3-wire" to "4-wire" or vis-versa. People deal with this all the time with new or old clothes dryers connecting to new or old outlets in homes. It's 100% doable though and safe.

 

[Orangepeel]

You're missing a bit of information here.... Are you hard-wiring this ? I wouldn't.... Or is there an outlet involved ? I hope so ! Post pictures of the outlet, the plug, and the "cord".

It's not unusual to go from "3-wire" to "4-wire" or vis-versa. People deal with this all the time with new or old clothes dryers connecting to new or old outlets in homes. It's 100% doable though and safe.

I am wiring a cord so it can be plugged in. Here is the outlet. I don’t have a picture of the cord currently but it’s a 3 prong range cord.

 

[Hall]

Is it already hard-wired at the air compressor ? Can you see the hook-ups or terminal connector at the air compressor ? With clothes dryers or stoves that can accommodate 3- or 4-wire hook-ups, you connect or remove a ground strap at the device.

 

[Hohn]

I am wiring a cord so it can be plugged in. Here is the outlet. I don’t have a picture of the cord currently but it’s a 3 prong range cord.

View attachment 264791

Replace that with a NEMA 6-50R and your life will be easier. It’s the standard 3-prong now for 220/240v up to 50a.

Of course, I’m obliged to mention that an air compressor has an electric motor and neither your current receptacle, nor a 6-50R, nor even a 4-prong 14-50R are “HP motor rated.”

Depending on the HP rating of the electric motor, code will not allow wiring via receptacle to an electric motor because of the flash hazard of unplugging a loaded/running motor.

I’m not a sparky, and I’m not sure if the “motor rated receptacle” is relay 3hp or 5hp or what. And of course, code compliance isn’t necessarily an obligation to the DiYer. But if your house burns down and they trace it to improper noncompliant wiring, I’d hate to see someone lose out on the insurance claim they need.

Recommendation: strongly consider hardwiring to the breaker via motor-rated, enclosed shutoff switch, verifying wire gauge and breaker ampacity.

If you need to have a disconnectable connection, get a HP/motor-rated receptacle and plug.

 

[wwillson]

That's a NEMA 10-50r, which hasn't been allowed for about 30 years in new installations, because it does not have a separate ground. The NEMA 14-50 plug has replaced it, which has a neutral and a ground. The two diagonal receptacles are hots and the vertical middle receptacle is the neutral.

However, see Hohn's post above.

 

[Orangepeel]

This is the compressor and the cord. My plan was to wire this cord to the compressor and plug it in. Obviously I want to make sure it’s safe. The compressor is a 3.7hp

 

[Orangepeel]

That's a NEMA 10-50r, which hasn't been allowed for about 30 years in new installations, because it does not have a separate ground. The NEMA 14-50 plug has replaced it, which has a neutral and a ground. The two diagonal receptacles are hots and the vertical middle receptacle is the neutral.

However, see Hohn's post above.

So if I was going to stick with this receptacle how would I go about dealing with the neutral ?

 

[Hall]

Depending on the HP rating of the electric motor, code will not allow wiring via receptacle to an electric motor because of the flash hazard of unplugging a loaded/running motor.

I'd think the HP value must be pretty high before that applies as plenty of devices have motors and cords with plugs on them.

That's a NEMA 10-50r, which hasn't been allowed for about 30 years in new installations

There are hundreds of thousands of those outlets still in use. Isn't that 100% standard for clothes dryers and stoves in homes built 20+ years ago (unless someone updated things) ? I've had to deal with these when my son has moved and his dryer was 4-wire while the outlet was 3-wire, then another time they had an older 3-wire dryer but the house they were in had a 4-wire outlet. Heck, we just bought a new stove that was pre-wired for 3-wire installations. Our house has a 4-wire outlet and we had to adapt the stove (simply remove the pre-installed ground strap between neutral and the chassis) in order to hook it up.

 

[D60]

Does the compressor use 110V for anything? My understanding was that stoves and such only need a neutral because they're running a clock or a timer, etc? ....and thus they're using one leg of the 220 + neutral

If you're just wiring a motor I too would use a 6-50R/P. Ground the ground. This is how my 80 gallon compressor has run since 2003, and my RPC since 2007. I don't have a dedicated neutral in any of my 220 shop wiring.

 

[Rand]

yep going to be hard to ground with that setup.

 

[Orangepeel]

Going from this to a 6-50R just need to figure out where the wires go in the 6-50r

 

[D60]

Going from this to a 6-50R just need to figure out where the wires go in the 6-50r

View attachment 264853

The hots don't matter. I mean they'll be the straight blades but you can't mix 'em up. If you're gonna use that existing neutral it'll be the rounded spade (just like grounded 110) but I've only ever wired a 6-50 with a ground. I'm not a sparky -- I just know enough to be dangerous.

I think if you don't want to pull a ground from a service panel you could run a copper stake and clamp outside -- if this is an exterior wall that might be easier. However, I don't know how code would feel about that? We need a real electrician