Box Fill Calculation for 50 Amp Receptacle

[jonness]

I'm installing a NEMA 6-50 50 amp receptacle using 6 AWG wire (two hots and a ground). I installed 3/4" conduit and a 30.3 cubic inch box. Then I realized the box is too small.

6 awg = 5 ci x 3 = 15 cubic inches for wire
receptacle counts as 4 * 5 ci = 20 cubic inches for receptacle
total = 35 cubic inches needed in box

The box I installed has the screw holes for yokes as opposed to having the screws on the edge. Is there anyway to extend the box so I don't have to rip it out and start over?

 

[Chuckster in NJ]

You can use a BOX EXTENSION that screws onto the front of your 4 11/16" box.

FWIW..... "Sometimes" it is easier to install a new properly sized box.

 

[jonness]

Sorry, I'm learning as I go here. I had to rip it out one time before and am hoping the current configuration can be saved. Bending the 3/4" conduit is not my strongest skill.

I'm currently using a 4" square box. I don't see any box extensions at HD or Lowes that fit my style of box (with the screw holes for yokes as opposed to screws at the edges. I also don't see any boxes with side hangers big enough to meet NEC using #6 wire and a 50 amp double yoke plug.

The available extenders appear to all be of the variety that require corner screws (unless I'm just not seeing how to use them properly). It's looking like I'll have to rip it all out again, rerun the conduit, and use a box that allows an extender like the one in the photo. Unless, perhaps, Platt Electrical Supply has something that will fit.

 

[Don1357]

Lowes and Home Depot have them. Look online, asking the kids at the store is often worthless.

 

[jonness]

I checked online and in the stores. The only boxes big enough to fit I can find are the 4-11/16". But they don't have the side bracket for mounting to studs. It appears these are intended for flush surface mounting. Also, I'm not sure what covers to use for these.

I was also not able to find extenders that fit boxes with yoke front end screws (unless they install differently than I'm imagining).

I looked at a bunch of youtube videos to see what others were doing, and all of the ones I watched featured DIY'ers installing illegal wire sizes and/or box sizes. Apparently, nobody in the U.S. actually has a legal 240v 50-amp welder outlet setup in their garage. Or, more likely, I don't know what to look for.

Any help would be greatly appreciated.

 

[Shiftless]

Here is how it looked in back of my kitchen stove before I did the drywall repair. That’s a 4 11/16 size box with a mud ring to bring it flush with the front of the drywall.

 

[sberry]

Extensions would be the deal. Dont be a joker and cut the back of the box out with a plasma. Ha. Now you know, the right box is 4x4 deep made for cover.

 

[alfredeneuman]

You can use a BOX EXTENSION that screws onto the front of your 4 11/16" box.

The picture shown is not a 4-11/16 box.
It is a 2 gang switch box.
411 boxes have 8-32 threads on the corners of the box. It takes either a mud ring or a surface cover.
2 gang switch boxes have 6-32 threads spaced for the devices to screw directly to, which take the place of the mud rings. They're meant to be mounted flush to the drywall

 

[u2slow]

I'm installing a NEMA 6-50 50 amp receptacle using 6 AWG wire (two hots and a ground). I installed 3/4" conduit and a 30.3 cubic inch box. Then I realized the box is too small.

6 awg = 5 ci x 3 = 15 cubic inches for wire
receptacle counts as 4 * 5 ci = 20 cubic inches for receptacle
total = 35 cubic inches needed in box

This is for a welder, correct? Check the machine's manual for wire size guidelines.

You may be causing yourself more trouble than you need with 3x #6 conductors. EMT can serve as the EGC/bond in most cases; or, if you used a cable assembly instead, the bare wire would be smaller anyway.

 

[alfredeneuman]

6 awg = 5 ci x 3 = 15 cubic inches for wire
receptacle counts as 4 * 5 ci = 20 cubic inches for receptacle
total = 35 cubic inches needed in box

All you need for a 50A circuit is #10 ground.
If EMT all the way you don't even need a ground wire.

 

[sberry]

If I had to buy wire for this would have been 8 and 10. There is a lot of fuss over sizing but a good thing about larger wires is really connections, you can snug them right up without hurting the wire.

 

[sberry]

I think a new style outlet fits in the shallow box. A traditional brand name 6-50 really takes 2 1/8 plus a raised cover to fit right especially with big wire. A lot would simply depend on what wire I had at the time, what welder I was hooking up. Most welders today do not need a number 6 in pipe, doesnt need to be a true 50 circuit. Last 3 outlets I installed for specific machines were 10 in pipe, 50 breaker. Another one to the hoist was 10/30, added a welder outlet for a 180 mig. Hoist motor is a 30 breaker.

 

[sberry]

Like a lot of guys here not a fan of the legal minimum on these circuits but do ok with a size up and on some machines a 10 is 2 sizes.

 

[Chuckster in NJ]

The picture shown is not a 4-11/16 box.
It is a 2 gang switch box.
411 boxes have 8-32 threads on the corners of the box. It takes either a mud ring or a surface cover.
2 gang switch boxes have 6-32 threads spaced for the devices to screw directly to, which take the place of the mud rings. They're meant to be mounted flush to the drywall

Good catch!

 

[u2slow]

Like a lot of guys here not a fan of the legal minimum on these circuits but do ok with a size up and on some machines a 10 is 2 sizes.

Heh. Yup.

The Miller Thunderbolt XL (stick) machine I wired up last week was nameplated at 47.5A@230V. Because of the low duty cycle it allows a #12 circuit up to 87' on a 70A breaker. The 6-50A cord was a #12 too.

I upgraded it all to #10 because we had it; tested out fine on a 40A breaker.

 

[Terry D]

Check me if I'm wrong. Since you ran conduit, # 8 THWN is good for 50 amps

A 4 x 2 1/8 box can have 10 #8's

Receptacle 4

Grounds 1

2 Hots 2

Total 7

Although not the box i would use, I believe your box meets the minimum requirements

 

[jonness]

Check me if I'm wrong. Since you ran conduit, # 8 THWN is good for 50 amps

Although not the box i would use, I believe your box meets the minimum requirements

I believe you're correct. I bought the wire prior to realizing there were box fill limits but I could switch out the wire. Out of curiosity what box would you recommend using?

 

[sparky 1971]

I believe you're correct. I bought the wire prior to realizing there were box fill limits but I could switch out the wire. Out of curiosity what box would you recommend using?

A 4X4X2-1/8 box (Raco 232, 235, 236, 237) with either a 2 gang mud ring that will allow it to finish flush with the wall or a raised cover (Raco 810c) if surface mounted. There are brands other than Raco, I just know Raco part numbers.

 

[Terry D]

I believe you're correct. I bought the wire prior to realizing there were box fill limits but I could switch out the wire. Out of curiosity what box would you recommend using?

I agree with Sparky 1971. The mud ring will give you a little extra depth. The box you posted is not set up for mud rings. When you mount the bracket to edge of the stud, the box will stick out 1/2" to be flush with drywall. A 4x4x2 1/8 mounts flush with the stud, the mud ring brings it out flush with the drywall. They make these boxes with side brackets to.

Sometimes, if running #6, I will switch to a 4 11/16 box

 

[jonness]

or a raised cover (Raco 810c) if surface mounted

I'm thinking that direction makes sense, since I'm using it in an unfinished wall. The cover would add 6.5 cu. in. capacity, which would make the total area in the box:

30.3 + 6.5 = 36.8

Thus, it would accommodate the #6 wire.

I already have a similar Steel City 30.3 cu. in. box and a steel city cover that adds 5.0 cu. in. I didn't use it previously because I didn't realize the cover counted as additional capacity.

Thanks to everyone for their help!

 

[sberry]

I ran across one where a guy had drilled 4 holes in a cover and screwed it on.