Voltage Detector through Drywall
Design2Reno
| Posted in Tools for Home Building on
I will be performing a renovation on an older home and may replace some old electrical wiring. I am looking for a detector that can detect regular home voltage through drywall so I can carefully cut a path to remove the old wiring.
Thanks in advance.
Replies
My cheepie Stanley studfinder detects wiring also.
Most of your non-contact voltage detectors will work through plain (non-foil-faced) drywall. Heavy plaster or any surface with lots of metal in it will cause problems, though.
Note that "hot" romex/K&T is much easier to detect than metal conduit or BX, and "cold" romex/K&T would be very hard to detect.
Is the wall sheet rocked? If so, what I do is take my sabre saw and break off a blade so that it sticks out only 1/2" to 9/16" with the saw blade all the way down. That way I can cut out the sheet rock. Even cut right across 2X4's and I don't have to worry about hitting anything inside the wall.
My question is, why open up the walls just to remove the old wiring?
If you're abandoning wiring in walls, it's perfectly acceptable to disconnect it at the source end (like where it goes into the wall from attic or basement), and leave it.
Just make sure that it's disconnected from power at an accessible point. With knob and tube, you can wire-nut the end at the last remaining knob and tape well . For BX or loomex (cable with cotton and bitumen sheath, also called "rag & tar"), disconnect at the last upstream box still in service, and remove the abandoned cable from the box.
At the far end, wirenut and tape off the abandoned end, and put a label/flag on it saying "dead & abandoned".
Make sure it is dosconnected. Look for goofy things like circuits that are fed from two breakers (on the same leg, of course), or set up in a ring or loop, where power comes from two directions, or that might be switch or thermostatically controlled. The first two situations aren't right, and aren't normal, but they happen--often accidentally, occasionally by intent. It's amazing how messd up electrical wiring can be and still function normally.
If you want to remove the old wiring and run new wire in it's place--I can see that, but really old wiring (K&T) was run VERY differently than romex. The hot wire and the neutral didn't run together, i.e., were often run on different sides of a stud. So trying to be surgical about opening walls to re-wire, and remove old wiring, is pointless, IMHO. My experience--and I've rewired a lot of old houses--is that you either abandon the old wiring in place and fish the new wires in, making a minimum of holes to run the new cable, or you lay waste, and open the walls up completely.
One think to keep in mind about removing old wiring--those old porcelain knobs in K&T are very hard and brittle. You may want to remove one or two carefully with the wire attached (especially a splice--soldered and taped), just to preserve a bit of history of the house. Then it becomes an exercise with a framing hammer and safety glasses. But, watch it when using a hammer to smash the knobs. A steel hammer on the porcelain is like a flint and steel. It can generate some pretty good sparks. Either keep the area broom clean or make sure you're around long enough to notice a smoldering spark in amongst the debris.
Cliff