That's panned joist - a duct made by applying sheet metal across the bottoms of two adjacent joists. The staples are going into the wood on the side and through the metal and into the wood on the bottom. - Jim Katen, Oregon Somehow though, that entire panel seemed electrified. If you brought the voltage sensor anywhere along it.... BEEEP!!!! [:-bigeyes If you're talking about those non-contact volt sticks, it might not have been telling you that the entire panel was electrified. Those testers aren't really voltage detectors, they're electric field detectors. The ungrounded circuit was probably inducing a field in the nearby metal. It's very common. On the other hand, maybe it was all electrified. The only way to know for sure (safely) is to use a real tester on it. - Jim Katen, Oregon Oh yes, 3 different voltage/electric field sticks. Mind you, with an electric field 5 feet away from the actual circuit you get an idea that something is not quite right in bubbatown. It seems like we have the whole houses amperage coming through that hole behind a heating pipe, stapled to a metal duct - ungrounded going from 3 to 4 wire, beside a septic line that was duct taped at the vent, spliced twice, held up by bent nails, spliced without a box, spliced in a box without a cover and all hidden behind drywall. The same owner also his oven hood wired with the hot energizing the ground. Had 40 amps #10/3 (yes - 10# going to a light socket (with a 13w bulb in it), an outdoor light that didnt match the box so he just screwed it onto the soffit, #10 wire going to a single outlet in the kitchen -(not on the counter - but not necessarily unreasonable)- also 40 amp - buried junction boxes and a bunch of other crazy stuff. Needless to say, I have to rewire my house when I can afford to. I've done my best to get it all closer to code.