Question on 240v outlets

Wiring up my new shop with 240v single phase which will power VFDs, 240v single phase items like my compressor etc. Ran 4 conductor cable but after buying 30 amp and 50 amp outlets discovered that the 4 wire 125v/250v versions don't fit in a standard work box but the 3 wire 250v only outlets fit fine. The only box I could find that would work is a metal square box with a faceplate that centers the outlet and doesn't cover the inevitable gap in the drywall around the box. Yeah, I can fill the gap with compound and screw with it enough to make it look half way decent if I have to. In my old shop I used the 3 wire outlets so didn't realize that 4 wire would be an issue.

So while the aesthetic issue isn't a big deal, it brings up the question - Is there any reason I might need the 4 wire 125v/250v outlets in a hobby shop?

Thanks.
Steve.

I live fine without 4-wire outlets. I had one once upon a time, but since have abandoned it. It was dedicated to my home-made table saw/router table. The tablesaw had a 120-V outlet on the side for the router and a vacuum cleaner. The 240-V table saw motor and the router/vacuum were powered from the single 4-wire outlet. Now I just have a bunch of 3-wire 240-V outlets and 3-wire 120-V outlets. In all cases, I got away with one less wire because I used the EMT for the ground path.

rklopp:

The National Electrical Code does not now allow use of EMT as the safety ground. There must be a ground wire no smaller than the current carrying conductors.

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My opinion is with the 4th wire (neutral) you have a legitimate way to get 120vac if you need it without a control transformer.

With only 3 wires, the ground must not be used to get 120vac......

This would probably be most useful for machine lighting (integrated) but of course those could be plugged into other, dedicated circuits.

The only box I could find that would work is a metal square box with a faceplate that centers the outlet and doesn't cover the inevitable gap in the drywall around the box. Yeah, I can fill the gap with compound and screw with it enough to make it look half way decent if I have to. In my old shop I used the 3 wire outlets so didn't realize that 4 wire would be an issue.

Click to expand...

Yeah, this is kind of a sticky point. I like using the metal duplex boxes with that mud ring that makes it a single box, as it gives TONS of room to do the wiring inside. If you get a 4 wire range outlet (is that the 50amp 4-wire you're referring to?), or even a 3 wire dryer outlet, then you can get a "fat" faceplate that covers all of the metal box. It's the size of a blank duplex cover, but with a hole in the middle for one of the two sizes of outlets I listed above. The outlet should have a four-screw pattern on it that matches these "fat" faceplates. I got mine at H-D, but most hardware places seem to have them as well.

If you get a different 240V outlet that needs a different size hole in the faceplate, you may have to buy a blank duplex metal faceplate and cut your own hole - or special order it. I have several L14-30 twist-lock receptacles for my 240V single phase (4-wire), and I "think" (don't quote me on this) that the hole size needed in the faceplate is different from BOTH the sizes easily available from dryer or range outlets.

Chad

P.S. You probably already knew this, but with the metal boxes (and assuming wood framing), you install the front of the box flush with the framing, and then install a mud ring (thing that converts your duplex metal box to a single box)with a lip equal to the thickness of drywall you expect to put up, then install the outlet, then the faceplate over the top.

Gar, when was the rule about not using the EMT as ground put into effect? I could swear that my 2005 copy of the NEC talks about how EMT connections must be made with ground wire "jumpers" to ensure a consistent connection between joints.

Yes of course use the 2 gang metal outlet box. In fact if you can find the right P-ring (plaster ring) get the 4 11/16 deep boxes.

The box is set behind the sheet rock and the P-ring protrudes through the sheet rock. You can select from a variety of P-ring styles but I use the 2 gang made to hold 2 standard receptacles. You will find all your 30 and 50 amp 240 volt receptacles will have the 4 screw holes to fit directly into these. Finish it off with the 2 gang stainless steel covers.

The extra large boxes give you plenty of room for splicing in your branch receptacles. You can have several outlets on each circuit depending on the demand needs.

As for the 4th wire, I use it in my shop because once the sheet rock goes on you can’t change it easily if you need it for a given piece of equipment.

gar
When was the ground wire size changed from a min of 1 size below the conducter?
mike

<<<gar
When was the ground wire size changed from a min of 1 size below the conducter?
mike >>

For circuits above 50 amp I believe

EMT can be used for a ground but it is not advised as these tend to fail over time.

Steve F

If the walls are still open you might want to consider pipeing in vacume along with power and air. I think Home Dippo can order or provide you with the special sweeps you need for vacume, but sure wish now I had done it

Use the L14-30's. You can put two in a standard double work box. I did this in my shop. Then take a standard double switchplate cover and bore the switch slots to match the outlet profile. I think I made 10 or 12 of these for my shop. I just screwed the plate down to a wood block, clamped them into my mill vise and used a boring head to trepan the hole. It took longer to describe than to do one. Pretty easy.

For anything small like a air compressor or a welder I use a Heavy Duty 3 prong outlet like for a heavy duty clothes drier or electric oven.

My complaint with the round ring type 4 prong outlet is that if it is somewhere where people can trip over it, they will. Usually tearing the cord out of the socket. After a few times it ruins the plug or the socket. The 3 prong outlet is so heavy that all it does is pulls the cord side out of the outlet. You just plug it back in and you are back in buisness.

I even have a Gen Tran Switch on the shop that plugs into a regular " Heavy Duty" 3 prong outlet that runs all the lights and 110 outlets when the power goes out.

When I did some research on earth ground resistance several years ago one of my references was the NEC2002 Handbook in our library.

I will have to go back to the library to get a specific reference on the ground wire requirement. It might have been in Article 250 of the NEC2002 Handbook around page 178.

My primary reason for the study was to get information on machine ground relative to noise. This I have discussed on my web site www.beta-a2.com on the NOISE and GROUNDING page.

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