3 wire Compressor to 4 prong recepticles

[1TonJeep]

I am moving into my new shop and the electrician outfitted the 3 240v outlets with 4 prong recepticles, the top being a ground, a flat up and down blade on each side and an "L" shaped slot on the bottom.

sort of looks like this:

O
I I
L


My compressor is 240v 15 amp but only has space for 3 wires, black white and ground. My question is how do I wire the old compressor to the new recepticle with its black, white, red and ground wiring?

I only know enough about electricity to know that I dont know jack sh*t about electricity!

Thanks for the help

[ptrautne]

I am moving into my new shop and the electrician outfitted the 3 240v outlets with 4 prong recepticles, the top being a ground, a flat up and down blade on each side and an "L" shaped slot on the bottom.

sort of looks like this:

O
I I
L


My compressor is 240v 15 amp but only has space for 3 wires, black white and ground. My question is how do I wire the old compressor to the new recepticle with its black, white, red and ground wiring?

I only know enough about electricity to know that I dont know jack sh*t about electricity!

Thanks for the help

Replace the 4 prong recepticle with a 3 prong and you will use the ground(green or bare) black and red. Tape up the white wire because it is only needed for 240V tools that also use 120V

[u2slow]

The 'L' prong is the white wire.... it won't get used on your 240V compressor - just use the red, black (the 2 'I' prongs) and the green (round/u-shape prong)

That style of receptacle is usually on a 30A breaker. You should downsize it to what the compressor wants.

[redsandman6]

the plug is for 3 phase. your compressor sounds like it is single phase or 2 wire plus ground. 3 phase has 3 wires plus ground the other guys are right you only need to use two of the wires the other wire will still be hot so use a wire nut on it so no one gets hurt

[1TonJeep]

OK,

Can I do this:

Since the plug that goes into the 4 prong recepticle has a interchangeable bottom prong (either L shaped or flat blade) can I just not put either in there then wire my compressor to the ground and the 2 flat prongs on the sides of the plug? This way I dont have to do anything to the recepticle as the plug will not have a prong inserted into the bottom slot, thereby only using the black red and ground.

yes, it is 240v single phase.

thanks for the speedy assistance!

[4xtoy]

The 4 prong recept is code now for all electric ranges and dryers. Because these appliances use not only 240v but also 120v for timers and lights. Your cheapest solution would probably be to get a male plug that matches the recept and cut the end off the cord and rewire the cord, leaving the neutral or "L" shpaped prong with no wire in it.

[4xtoy]

The 4 prong recept is code now for all electric ranges and dryers. Because these appliances use not only 240v but also 120v for timers and lights. Your cheapest solution would probably be to get a male plug that matches the recept and cut the end off the cord and rewire the cord, leaving the neutral or "L" shpaped prong with no wire in it.

[u2slow]

Since the plug that goes into the 4 prong recepticle has a interchangeable bottom prong (either L shaped or flat blade) can I just not put either in there then wire my compressor to the ground and the 2 flat prongs on the sides of the plug? This way I dont have to do anything to the recepticle as the plug will not have a prong inserted into the bottom slot, thereby only using the black red and ground.

Yes. That will work. You should still look into the breaker size though.

[1TonJeep]

thanks all. i appreciate the help.

i checked the breaker and it is a doubled 20amp, so i am guessing 40amp? The compressor only requires 15a, so what's the fix? Last thing I want is :smokin:

Mike

[u2slow]

20A is 20A. The fact that its a double (i.e. 2 pole) means its a 240V circuit instead of 120V.

IMO the 20A is the smallest/safest breaker you can run for your 15A load without nuisance tripping. :)

[PAToyota]

The 4 prong recept is code now for all electric ranges and dryers. Because these appliances use not only 240v but also 120v for timers and lights. Your cheapest solution would probably be to get a male plug that matches the recept and cut the end off the cord and rewire the cord, leaving the neutral or "L" shpaped prong with no wire in it.

Correct. The 4 prong recept. is code ONLY for appliances that use both 120V and 240V. Any electrician who wired up a shop with 4 prong recept. has no idea what he is doing...

[CaglezXJ]

don't know if you have finished this project yet. I just wired my welder and compressor up over the weekend. What type of plug comes off your compressor? is it a 3 prong, 4 prong or a regular male plug with one of the tabs turned side ways? 4 prong doesn't make alot of sense in a garage. Not around here anyway. But very easy to change. Like they said above 20amps is 20 amps , if your compressor calls for 15 get a 20 amp if calls for a 20 amp get the next step up. This is cause when the compressor/etc starts you get a inrush. In rush is a suddon pull of amps when starting or loading up a electrical device.

Couple good plugs. the twist type, which want pull out, I believe they are rate at 460 volts. Don't let volts fool you, as long as you don't go over what it is rated you are good. The plugs I m talking about has 3 or 4 prongs shaped in a circle, you push in and twist. want pull out. You can use anything rated higher than you want, find a plug you like. Whatever fits your job.

house power, or for your garage is more than likely 110, and 220/230v whatever you want to call it. The motor on the compressor should show you the amps it pulls, make sure it is max amps: install your breaker. Sense you don't know much about electricity, and to be safe turn off the main breaker. Install your breaker. remember get a double pole . From that all you need is your 2 main power wires and a ground. 10-2 would be great but 12-2 is good as well. Now just run each wire to the female plug. doesn't matter which side you put it on, just make sure you put your ground where it goes. If you change the male plug end on the compressor just do the same. And you are good to go. The colors don't make a big deal as long as you remember... My wire was black and white with a bare ground. Keep it Simple Sweet!!

Kinda lenghty but hope it helped.

[u2slow]

CaglezXJ - you've inspired me to elaborate on my recommendations.... :D

(sticking withe Canadian Electrical Code - cuz its all I have :p )

Motor supply conductors - min. 125% of full load current
125% * 15A = 18.75A min. ---> 20A ----> #12 wire

Overcurrent device (breaker) - max. 250% of full load current
250% * 15A = 37.5A max. ---> 30A (closest smaller size)

However manufacturer's ratings override the Code rules.

Maximum circuit length for #12 wire while maintaining acceptable voltage drop (using 3% here) is ~120' from the main panel. For #10 it goes up to ~190'. For#8 its ~300'.

On the twist-lock connections, each voltage and current rating is unique... and you will pay extra for the ones with higher ratings. In general, they are quite costly.

Dryer plugs (14-30R/P) are insanely cheap... probably the main reason why the electrician used them. There is also no shortage of 'free' cord ends at the dump/xfer-station. :D

The two most common connections I see on factory cord-connected 240V compressors are the NEMA 6-20, and 6-30.
http://www.evenheat-kiln.com/technical/recept/620R.gif http://www.evenheat-kiln.com/technical/recept/630R.gif

If you have, or plan to acquire more 240V equipment, now is a good time to standardize on your connections. ;)

[CaglezXJ]

CaglezXJ - you've inspired me to elaborate on my recommendations.... :D

(sticking withe Canadian Electrical Code - cuz its all I have :p )

Motor supply conductors - min. 125% of full load current
125% * 15A = 18.75A min. ---> 20A ----> #12 wire

Overcurrent device (breaker) - max. 250% of full load current
250% * 15A = 37.5A max. ---> 30A (closest smaller size)

However manufacturer's ratings override the Code rules.

Maximum circuit length for #12 wire while maintaining acceptable voltage drop (using 3% here) is ~120' from the main panel. For #10 it goes up to ~190'. For#8 its ~300'.

On the twist-lock connections, each voltage and current rating is unique... and you will pay extra for the ones with higher ratings. In general, they are quite costly.

Dryer plugs (14-30R/P) are insanely cheap... probably the main reason why the electrician used them. There is also no shortage of 'free' cord ends at the dump/xfer-station. :D

The two most common connections I see on factory cord-connected 240V compressors are the NEMA 6-20, and 6-30.
http://www.evenheat-kiln.com/technical/recept/620R.gif http://www.evenheat-kiln.com/technical/recept/630R.gif

If you have, or plan to acquire more 240V equipment, now is a good time to standardize on your connections. ;)

NEMA 6-50 same as the photo on the right but with the prongs up and down. Good post with pics, I was lazy.