A fundamental tenet of electrical wiring safety is that all connections (of AC household wiring, typically 120 or 240v) be enclosed in rated electrical boxes.

However, ceiling light fixtures and fans are typically mounted to 4" diameter circular boxes (heavier-duty ones for fans and other extra-heavy things). I note that very often the top (or "bell") of such fans and lights are considerably greater than 4" in diameter. Thus, there is an annulus of exposed material around the perimeter of the round 4" box, and the connections of the fan or light to the incoming wiring (typically NM-B or "Romex") are not completely enclosed.

Is this acceptable ? Is it ok to simply push the wirenuts (which make the connections) up into the box ? Should one fabricate a piece of sheet metal which fits flush against ceiling surrounding the box ? Or one of the available decorative such pieces ?

  • My current issue is replacing a 6" Halo recessed "can" with an ordinary luminaire. I plan to mount an old-work 4" round box in a piece of plywood glued above the 6" hole (covering it, so there's not a big air leak). In fact, the diameter of the new luminaire is considerably greater than 6", so there will be plywood exposed around the 4" box, plus drywall exposed around the 6" hole. Jan 19, 2022 at 6:15

1 Answer 1


This is acceptable.

NEC 410.23 states "Covering of Combustible Material at Outlet Boxes. Any combustible wall or ceiling finish exposed between the edge of a luminaire canopy or pan and an outlet box having a surface area of 1160 mm^2 (180 in^2) or more shall be covered with noncombustible material."

So unless the luminaire canopy is greater than 15" diameter, there need be no covering on the exposed ceiling.

  • Seems like this could be interpreted to mean no box is needed. Jan 19, 2022 at 7:40
  • 1
    Not sure what your comment means but the box is required the canopy covering the box the wire nuts can be in that zone protected by the canopy + for the code ref.
    – Ed Beal
    Jan 19, 2022 at 8:08
  • I'm unclear if the wire nuts themselves (the "connections") need to be pushed up INTO the box, or whether they just need to be in the volume enclosed by the box, the surrounding ceiling, and the luminaire canopy. Sounds like you are saying the latter. If this is the case, then what is the box really doing ? It's less than 16 in^2 of the 180 in^2 area of the ceiling that's allowed to be unprotected combustible material. Jan 19, 2022 at 18:38
  • The nuts can be below the box but the box is still a required part to stop materials from falling in the hole and to contain sparks and or flames no box and you can have a attic fire much easier, if you can put the connections in the box but after thousands of light fixtures you would quit fighting to get them in there but I can say I haven’t seen a case that a fire was started because of connections below the box inside a canopy including several where 14 awg wire was used on 20 amp circuits that did burn open, i won’t say the type of person that did the wiring but they did not have a license
    – Ed Beal
    Jan 20, 2022 at 0:33
  • Well, I am one of those DIY people. Though I also am an electrical/computer engineer, so have a pretty deep knowledge of electricity. These very practical issues, as well as the code issues, do confuse me from time to time though. Jan 20, 2022 at 2:20

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