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What is the minimum box volume required for a L5-30R receptacle? This is a 125V, 30A, single phase twist-lock receptacle. Is a 4" box required or is a 2" single gang box acceptable. Also are there any special mounting requirements due to the twisting action required. Can the box be tabbed directly to the drywall opening with no attachment to wall framing (for after the fact installation). Thanks in advance.
The manufacturer may have instructions but the NEC is silent on the mounting. Box fill is 2 conductors allowance, same as any device. That doesn't mean it will fit.
Common sense says use a box that has enough room and mount this securely. Twist lock implies there will be some extra strain on the cord and you won't simply pull out the plug cap. We used a lot of twist lock and usually put them in a 4" box with 4 screws per device.
Quote
Can the box be tabbed directly to the drywall opening with no attachment to wall framing (for after the fact installation).

Depends, I learned here that if you are cutting into a firewall, the box must be attached to the framing of the wall.

I think Roger or Bob(iwire) have the link, it is not in the code book, but a building code if memory serves me right.
Iwould use a deep 1Gbox to allow the wires some room.

If you are worried about the twisting working the old work box loose after awhile look at using one of the new smart box style old works that screw to the side of the stud.

Arlington makes one, check www.aifittings.com or www.smartbox.com for another brand.
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