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I searched on this site and also google and couldn't find anything definitive on this.

My GC installed a single-gang outlet box behind the range for a NEMA 14-50R outlet. Most of the 14-50R outlets require a two gang box, but I found this one by Preferred Industries that says it works with a one-gang:

https://www.wilmar.com/Sku/35-57070/preferred-industries-3-pole-flush-mount-range-receptacle-straight-blade-4-wire-nema-14-50r-black-125250-volts-50-amp-076335241999

Is this ok? I know there is a way to calculate the fill requirements to get minimum cubic inches of an electrical box but am not sure how to do it for this type of outlet.

Here is a matching one-gang wall plate: https://www.wilmar.com/Sku/94-7470/flush-mount-1-gang-wallplate-white-078477836781-80528-w

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  • How deep is the 1-gang box in question?
    – ThreePhaseEel
    Jul 25, 2018 at 11:41
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    I'm pretty sure it won't fit just from looking at it because I just installed two of these outlets (one 30A one 50A) and I had to use a metal 4"x4" box which isn't really 1 OR 2 gang
    – The Evil Greebo
    Jul 25, 2018 at 11:43
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    It's OK to use that device with a single gang cover plate, but that doesn't mean a single gang device box is allowable. You would use a single gang device ring on a 4x4 (or larger) box with this receptacle if you want to look at a single gang cover rather than a two gang.
    – batsplatsterson
    Dec 18, 2019 at 14:23

3 Answers 3

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Both answers above are incorrect. You need a 2 gang and not just any 2 gang, calculate volume as follows:

  • (3) 6 AWG conductors @ 5 cu in each = 15 cu in

  • (1) 10 AWG ground = 2.5 cu in

  • (1) NEMA 14-50R (2 straps, 2 conductors/strap) = 4 * 5 cu in = 20 cu in

  • (1) wire connector/clamp = 5 cu in

  • Total = 42.5 cu in

For background the number of straps is dictated by the receptacle device, 14-50R is a 2 strap device. Each strap counts as (2) conductors of the largest size present in the box (6AWG = 5 cu in). The cable connector, if located inside the box, which is assumed for old work installs, will count as another conductor of the largest size present (6 AWG = 5 cu in).

I have not found an 2g old work box that accommodates 42.5 cu in so use a new work box and drywall work will be required but luckily it will be hidden behind the stove so most can DIY that without a big ugly mud job visible.

Common misinformation I have seen is that you can clamp a 6/3 cable in any 3/4" knockout. This is not true, the Arlington NM842 can handle a 6/3 in a 3/4" KO so that's what I use. If using anything else check packaging and it should say the acceptable wire size. Every specialized range box I have seen with a built in clamp CANNOT handle a 6/3. The manufacturers intentionally do not list this on their packaging so I guess this is just a gap in the industry. I am still researching but damn this is a crapshoot if done to code.

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    Are you sure you're calculating the device fill from the 14-50R correctly? I've never heard of a "two conductors/yoke" rule before
    – ThreePhaseEel
    Jan 12, 2022 at 1:58
  • 314.16(B)(4) For each yoke or strap containing one or more devices or equipment, a double volume allowance in accordance with Table 314.16(B) shall be made for each yoke or strap based on the largest conductor connected to a device(s) or equipment supported by that yoke or strap. A device or utilization equipment wider than a single 50 mm (2 in.) device box as described in Table 314.16(A) shall have double volume allowances provided for each gang required for mounting.
    – Justin
    Jan 12, 2022 at 16:37
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    Yeah, I'm familiar with 314.16(B)(4) -- turns out, I thought that 14-50Rs were narrow enough not to be two-strap devices, but they are wider than the 2" given in that code section
    – ThreePhaseEel
    Jan 13, 2022 at 0:11
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Box fill calculations say you need a volume of 5 in³ per AWG 6 conductor that lands in, or is spliced in the box, plus an allowance of 2 wire volumes (5 in³ each) for the receptacle itself. For a 14-50R receptacle, you will have 4 conductors, plus 2 for the receptacle, means that 30 in³ is required.

A 2g remodel box is only 25 in³, which is not legally large enough, but is exactly what we use for every Tesla charger we install. It is difficult to squeeze the wires in and get the receptacle screwed down, so I recommend installing the whole assembly before mounting the box in the wall so you don't break the drywall with the force of the screwdriver pressing against the screw head.

I'm starting to reconsider this practice and may start using a 4"x2-1/8" square box, which is the minimum actually approved for this application.

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  • I always use a self contained box for tesla/ev chargers... You can mount them over a single or double gang and bring wires in through the back if you aren't running conduit... amazon.com/Talon-LGP1S-Enclosed-Outdoor-Receptacle/dp/…
    – T Taylor
    Dec 18, 2019 at 18:51
  • @DanielGriscom Please read posts completely before commenting, instead of robotically posting canned comments. This post contained a clear code-of-conduct violation that should have been addressed, not thanked.
    – nobody
    Jan 12, 2022 at 2:55
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Most 14-50 nema outlets look like they need a two gang... but they don't. They can fit in either. However we use a two gang for those behind a range typically. If you need more room and have the space behind the range, you can install an adapter box which is a metal 4 square box that would mount over the single gang box, you would need a metal industrial cover for it with a nema 14-50 size opening.

Such as this.... https://www.garvinindustries.com/electrical-junction-boxes/4-square-junction-boxes/2-1-8-in-deep-extension-rings/53171-sub

and this...

https://www.garvinindustries.com/covers-and-device-rings/4-square-covers-device-rings/industrial-covers/g1934

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