Covering screws used to mount receptacle boxes

Question

Should screws that are used inside a receptacle box to mount it to a stud be covered by tape or some non conductive material?

Answer 1

TL;DR No

First of all, I recommend using metal boxes. In which case the screw would be not better/worse than the rest of the box. If you use plastic boxes then the screw head won't matter because it is not connecting with any conductive anyway, unless you have metal studs (unusual in the US for residential construction, but not impossible).

But even using the metal box/metal screw example - where any stray wire could contact the box:

• If the stray wire is ground then it doesn't matter, because the box is grounded.
• If the stray wire is neutral then it does matter a bit, though if there is any GFCI protection then that will kick in to prevent any serious problems.
• If the stray wire is hot then it matters a lot, which is where the difference between metal and plastic boxes comes into play. With a properly grounded metal box, the circuit breaker will trip. With a plastic box, that screw won't actually complete a circuit because the screw is not going anywhere that it can complete a circuit, unless you have metal studs. If you have metal studs and a plastic box then it gets rather interesting, because if the studs do not themselves complete a circuit (incomplete grounding) then you have now made a portion of the building structure hot...which is not a good thing.

So if you have metal studs then use metal boxes, and don't worry about the screws. If you have wood studs then use metal boxes or, if you must, plastic boxes, and don't worry about the screws.

What can be helpful in a very tight metal box is to put a wrap of electrical tape over the screws on a receptacle or switch. Some would argue against it, but done properly it can make things easier, particularly if you have to adjust the receptacle or switch to make everything line up properly. But often if the box is an older, smaller, box it is better to just replace it with a larger box.