Electrical Wiring in the Home/POSSIBLE NAIL HITTING WIRE
MC7 wrote at 2013-02-15 18:13:53
Disconnect power to the switch, then remove the wall plate and switch. Look inside the box and see if the wiring (plastic jacketed ROMEX most likely) enters from the bottom or top. If from the top only, you probably had hammer shock. However sometimes there may be another run stapled to the same stud and this run bypasses the switch box so look one. If the only wiring is that which enters the top of the box, and there are no wall outlets below the switch, install switch and wall plate. You are done.
If there is a wall outlet under and inline with the wall switch, skip the switch instructions above and instead start at the outlet.
If wiring enters from the bottom, or from top AND bottom, use a flexible inspection camera to look down the wall cavity. If wall is insulated this can be difficult to impossible depending on length of the camera's fiber optic flex shaft.
Alternatively, look in the wall box and note which side of the box is the wall stud. Put a length of painters tape on the wall surface such that the bottom edge of tape abuts the baseboard - this is to mark the top edge of the baseboard for a later step. Remove the baseboard. Making sure the top edge of the hole you are about to drill is well below the tape (top of the baseboard), drill a half inch hole about 2 inches away from the wall stud and again use the camera. Or drill/cut a larger hole and use a dental mirror. If necessary, gradually nibble away the dry wall towards the stud until you can see if there is wiring attached to the stud. If there is no wiring, reattach the baseboard and install switch and wall plate. You are done.
If there is wiring, with power OFF, take a nail and push it through the hole made in the sheetrock and use this as a visual "guide pin" reference. If you hit wiring, unless you drove the nail on an angle, you missed the stud and maybe hit the wiring you are concerned about if it exists. Looking through the hole you drilled/cut, try to see this nail and proximity to wiring.
If it looks like the wiring was in fact struck by the nail, you will need to replace / repair the wiring. Now may be the time to add either a wall outlet or even a stairway light as this may make a repair easier versus pulling new/replacement wiring.
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