Old Work Box

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For cutouts in plywood, as opposed to frame mounted receptacles.


Old work box in 60 seconds:



There is a known bug in most old work boxes - the clamps are too close to the edge and these must be cut out while using a hole saw for the round diameter.

  • Check.pngAdmissible parts - For resi, I prefer the 18 cu.in. 4” round, #C1-18 Slater boxes. A 3-3/4” hole saw is a perfect fit for it. The Slater box is actually rated for 20lb fixture support, so I really like to use these for wall mount fixtures if the canopy will cover them. The old standard 14 cu.in. 3-1/2” round T&B phenolic boxes are still great for lightweight low profile applications having only a few wires. A 3-5/8” hole saw allows the for the C-clamp and ears to set in perfectly. - [1]
  • Legrand - Pass&Seymour Slater - C1-18 box - [2]. Note that the clamp screws are recessed, allowing full coverage of flange with screws, up to 20 lb - no need for keyhole saw tab fixing.
  • Check.pngCheck.pngCantex seems to need 4" hole, OD is 4.4" so almast 1/4" flange on each side. Marginal but ok. - [3]
  • This Allied box [4] works to 15 lb, with wall material up to 9/16", with 3.5" hole for tight fit. But, you can't take this box out once you snap it in!
  • T&B phenolic - [5]


Note on dimensions - the outlet mounting screws form the outer edge. These screws are protrusions, or inside the box, but their outer dimension defines the height of the box. That appears to be 3-5/8". It is safe to do 3-3/4" as the 4 front tabs are larger than this. The locking tabs on the back are even larger.

It seems safe that 3.75 is a safe height of cutout, and 2-3/8" is a safe width (widths all appear to be 2.25").

  • 3-7/8-Inch Length by 2-3/8 [6]
  • 4-1/8 x 2-1/4 [7]
  • 2-3/4 in x 2-1/4 in [8]
  • 2.75 x 2.25 x 4.3 [9]
  • 3.65 x 2.3 x 4.3 [10]
  • 2.25 x 4.38 x 2.75 [11]

Allowed in New Construction



From [12]

Just a heads up, if the wall is fire rated the box must be secured to the stud regardless of the box listing. This is a building code issue not a electrical code issue.

I have no idea if the opening posters wall is fire rated.