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I've found the 'where' to drill a hole in the joist span to run wire across ceiling cavity (multi-story on first floor so no attic access). What I can't find is how does someone drilling from an access hole in the ceiling into a floor joist know that there isn't anything on the other side of the joist (e.g. stapled ROMEX on joist, etc.)? Example, if I have an access hole in my kitchen ceiling between joists 2 and 3 and want to drill through joist 2 to get to joist cavity 1 and 2, and I don't know if there's a previous remodel or wire-run stapled onto the non-viewable side of joist 2, how can I be sure nothing is there (is there a code or standard?...of course, you never really know without laying eyes on it and opening up the joist 1 & 2 cavity) but obviously would like to avoid additional work of opening a new cavity just to inspect).

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  • Some stud finder has an option to detect live wires. – user263983 Apr 14 at 11:32
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    Reach through the hole with a non-contact voltage detector. If it beeps, you know there's a live wire there. If it doesn't beep, you know... nothing. – FreeMan Apr 14 at 11:36
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    @FreeMan are you suggesting that the detector would work through a 1.5in joist? I'd say almost certain no beep, and I'd almost certainly know .... nothing. – P2000 Apr 14 at 20:18
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If it is at all possible, you make sure you can see the other side before you drill. In some areas fishing wires into an unopened space is considered concealed work and must be done by a master electrician.

That said, a few tricks I've seen used:

There are many types of electrical toner. I don't know the name of the one you want for this, we just called it an in slab or in wall toner, but it looks like a metal detector and you can sense wires 6 or 8 inches deep in something.

For holes into the top of walls where something may be stapled to the underside of the stud, you can use a hole saw without a pilot bit (only pilot to get started) and drill only part way through then smash out the plug.

You can also use a skinny volt ticker like the Fluke LVD1A taped to a stick to sense the bottom of a smaller hole before you drill through.

Depending on the geometry of where you want to check, a stud sensor with electrical sense has better depth than a volt ticker at low price.

You can get a cheap usb inspection camera for your laptop or phone and attach it to a wire to make a camera on a stick. Drill a hole somewhere safer, put the camera in, take a look.

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  • Thanks @K H for the in-depth response. I'll likely use an electrical sensor so long as it's appropriate for the joist thickness (in the case of double-joists). I was more or less wanting to know if there was a code that said something like, 'no wires can be stapled onto the bottom/top half/third/etc. or specific inches from end' to see if there was a general guideline (similar to rules about how thick a hole can be in a joist and also the placement of it with respect to top or bottom of structural joist. – habrockc Apr 15 at 2:04
  • What the code says in most cases is that concealed work shall be done by a master electrician. The word shall carries fairly absolute legal weight. Different volt tickers perform differently, so you should do a test to make sure you can sense a wire with the very tip through 1/4" of wood. Then probably use the hole saw method. Drill almost through and then use a flat blad screwdriver to break the puck out of the bottom of the hole. Sense before drilling through the last 1/8". If you have them, forstner bits are even better for safely getting close to the bottom of the stud. – K H Apr 15 at 2:13
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    Even if you don't sense anything, drill through as if you fully expect to hit a wire and want to avoid damage! – K H Apr 15 at 2:15

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