It was a great solution to what could have been a difficult situation between the electrician and the drywallers. Though, it was a little careless of the drywaller to lay board over the electrical box. Usually, they look for those things.
I agree with Beth, but Bob is right to question why the box was so far back that it could have drywall run right over it and not need a cutout. That is just plain poor work quality. Having done a whole lot of reworks of other peoples installations, it is clear that lazy construction practices make everybody else's work more difficult for many years to follow.
Of course, I am aware that if the box needs a cutout then the sheetrock installer needs to do more work, which does make the whole job take longer, but if the electrician needs to fight with a box that is set back to far, that also takes more time as well.
It is clever to use a portable radio with a ferrite loop antenna to detect the brush noise, but I agree the signal would not be significantly stronger at the box than along the wiring leading to it. Perhaps once this method had located the general area, one might use a metal detector, an RF based stud-finder, or even a pocket compass to find the exact spot. All this assumes that the electrician was not so sloppy as the dry-waller and used a traditional steel box.
in the old days we would just roll all the wires into the box, but later the electrical code required that for the rough-in to be complete the wires would be connected as they would be when the installation was complete except for the wiring device (outlet), so the hash would propagate from box to box, no problem. also a set of plans could locate the box to within a few feet, then use the transistor radio from there. the box location would usually give off a stonger signal due to the ball of wire in the box.
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