DIY Home Improvement Forum banner

1 - 16 of 16 Posts

·
Registered
Joined
·
6 Posts
Discussion Starter · #1 ·
Hello, I’m planning to convert the 240v receptacle in my garage to act as a junction box, and run wires from there out to my new air compressor. The receptacle has 3 color wires (see photos) and a ground to the box. My compressor has connection for only 2 color wires and a ground, not sure which 2 of the wires I would use.

Thank you for any help you can provide

Chris
 

Attachments

·
Usually Confused
Joined
·
7,269 Posts
It appears that the receptacle is using the neutral conductor as ground.
 

·
Super Moderator
Joined
·
21,812 Posts
It appears that the receptacle is using the neutral conductor as ground.
I agree. The original receptacle was miswired. However it doesn't matter for the new install. You have a ground in the box so use it as a ground for your compressor and cap the white.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #5 ·
Thank you! As far as the copper ground wire going to the air compressor, should I connect that to the white (neutral) wire since it is acting as ground?
 

·
Usually Confused
Joined
·
7,269 Posts
Thank you! As far as the copper ground wire going to the air compressor, should I connect that to the white (neutral) wire since it is acting as ground?

Does the conductor feeding the receptacle have ground conductor (bare/green)? As far as I know a white conductor cannot be repurposed regardless of how it connected at the other end.
 

·
Registered
Joined
·
9,502 Posts
It appears that the receptacle is using the neutral conductor as ground.
That is right, and it’s a common wiring method for a dryer. It’s known as ground over neutral. It’s a grandfathered wiring method in the NEC for 120/240v, with or without the ground in the box.

Since, the OP is apparently not using it, and is modifying the circuit by extending it, I’d recommend removing the receptacle and using a blank cover plate. Connect the hots and ground to the new cable, cap off the White neutral.

If he sells the place in the future, the compressor wire can be removed. A 4 prong 14-30r could be installed at that time as the dryer receptacle. 4 prongs have been required since 1996, IIRC.
 

·
Super Moderator
Joined
·
21,812 Posts
He said there is a ground connected to the box. He should use the red, black and bare ground. The white should be capped.
 

·
Very Stable Genius
Joined
·
4,480 Posts
May have missed it....but did op explicitly state the new compressor is 240V?
If so, I agree with advice above.
If it's 120V, op should clarify for new advice.

BTW, a disconnect such as motor/hp rated switch would also be a good idea.
 

·
Registered
Joined
·
6 Posts
Discussion Starter · #11 · (Edited)
CodeMatters - yes the compressor requires 240v (Central Pneumatic 60 gallon 5hp). The receptacle was used for a dryer by the previous owner, as was mentioned by Oso954. I’m amazed at how fast you all zero’d in on my situation, thank you all!

So hypothetically, Am I correct to say that to bring the existing receptacle up to code I would need to install a 4 pin receptacle ala the attached photo?

Chris
 

Attachments

·
Super Moderator
Joined
·
21,812 Posts
You only need a three pin receptacle if the compressor is 240 volts. But you could use the four wire if want. The neutral won't be doing anything.
If you want to use it for a dryer which requires 120/240 then you need the four wire receptacle.
 

·
Registered
Joined
·
1,656 Posts
There is no way to know how the previous owner used it for a dryer, but the existing receptacle is 50 amp 240 volts. What amperage is the new compressor rated? Ok, I looked a similar compressor which says 24 amps and to use a 50 amp breaker. You will be ok. Just follow previous advice.
 

·
Registered
Joined
·
2,715 Posts
Your circuit breaker needs to be changed to match the ampacity of the compressor (Whatever it says in its instructions). If that's unclear, post a nameplate of the motor and we'll figure it out. Probably 20A or 30A tops.

These sockets have names. The old one there was a NEMA 6-50, which is 50A ampacity. They also make a NEMA 6-30 (30 amp). That 4-wire socket would be a NEMA 14-30 or 14-50. If you need 20A, they also make a NEMA 6-20 (very common, and very familiar) and a NEMA 14-20 but that's rare.

If you cord-and-plug connect this compressor, either NEMA 6 or NEMA 14 will be fine. However the socket ampacity must match the breaker ampacity. (except for 40A breakers, they don't make 40A sockets, so in that case you use the 50A socket).


Thank you! As far as the copper ground wire going to the air compressor, should I connect that to the white (neutral) wire since it is acting as ground?
Nope, never. Neutral is not ground. Neutral handles normal current. Ground never handles current except during an emergency. People often mistake it because they see the neutral-ground equipotential bond back in the panel that connects them, but location is everything. Anywhere else, connecting them creates a safety hazard.

So cap that thing off if you're not going to use it! Don't cut it; it's very handy for a potential future installation.

Now if you were dealing with an obsolete dryer hookup that had an insulated neutral and no ground in the box, you could retrofit a separate 10 AWG ground wire back to the panel (or some intermediate points depending). But you'd still keep that white wire capped off regardless. You simply cannot use it here.
 
1 - 16 of 16 Posts
Top