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I am replacing some receptacles that are contained within metal electrical boxes in my shop.

Is it proper technique to wrap the outlet with electrical tape to prevent shorts with the grounded box (See New receptacle tripped/sparked for example)?

If wrapping the outlet is correct, does it need to be de-rated due to the potential higher temperature caused by the insulation effect of the tape?

  • Photo of box in question would be helpful. – The Evil Greebo Jun 15 '17 at 14:02
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If the box is grounded, there isn't a reason for wrapping tape around the box unless the receptacle is loose, and you have movement of the receptacle. This would be a poor way to correct the problem, because the tape on the box may come loose over time because of dampness in a workshop. The optimal approach would be, to use oversized screws to correct this. I would also use a metal box cover for the metal box.

Furthermore you may want to see if one of the outlets ARE GFCI protected type. You may or may not have water in your shop, but usually there can be a lot of dampness present in a shop. If one of the receptacles isn't GFCI then you may want to purchase a GFCI breaker for your box, and replace the breaker that powers your outlets. You could also use a GFCI receptacle for the GFCI (Ground Fault Circuit Interrupt), but it is normally limited to the number of receptacles depending on your local codes. Good luck!

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In my opinion, no, this is not "proper". If your receptacle moves enough when plugging thing in to short out to the box, then you have other problems. The receptacle should be rigidly attached, so that it does not move during normal use.

A mistake I have seen made, is where the unused screw terminals are not tightened down. Depending on the size of the box, this can put the terminal screw quite close to the wall of the box. Which means it only takes a slight bit of movement, to get the screw to make contact with the wall of the box.

Another mistake is to carelessly tuck the grounding conductors into the box, so that the bare ground can come into contact with the ungrounded (hot) terminals.

If you do decide to wrap the receptacle in tape, you should not have to worry about higher temperatures.

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There's no doubt it's a matter of "belt and suspenders" (redundant protection).

The main reason to do it is for the installer. You are in that box later, pulling that yoke out, and either a) whoopsydaisy, it turns out that circuit was not de-energized after all; or b) you are troubleshooting a problem which "lights up" things which should be off.

Once I definitely did turn off the right breaker (the breaker was unclipped from the bus), and bumped hot against ground, got a tiny arc flash. WTH? it was a tiny flash, so I connected it firmly, and voila, a fluorescent light on the circuit lit up. These things do happen.

Also, I have had cases where due to the shape of the box, you had close contact. That is particularly when dealing with the relatively shallow steel boxes and also Romex, where you have ground wires flopping about (which you do not in EMT). Worst case: side entrance of Romex into 1-gang.

As far as thermal derate, you are at the screw terminals, where there is a mighty slug of metal. No chance of overheat there (we aren't using the backstabs, right?) If it really bothers you, do a 30% derate off the 90C numbers. (This derate is already required; natively, 12AWG is good for 30A.)

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