Finally figured out why my garage circuit was acting up

I had a similar scare last summer working in my garage. I was leaning against a run of 3/4" EMT while moving some storage bins and felt that unmistakable buzz thru my forearm. When I pulled out the Fluke, I was reading almost 90 volts between the conduit and the concrete floor. It turned out to be an old Appleton round box where the ground screw had shaken loose over forty years of vibration from the shop compressor.

One of the wires had a tiny nick in the THHN insulation right where it entered the box. Like your T-slot outlet, those old cast iron fittings are incredibly sturdy, but they don't leave much room for error if the grounding path isn't perfect. I ended up pulling new 12 AWG wire through that whole section beacuse the old cloth-covered stuff was just crumbling in my hands.

I totally get wanting to keep that vintage look, though. There is somethig about the weight of those old Killark or Crouse-Hinds covers that modern plastic or stamped steel just can't match. I ussually try to sand them down and repaint if the threads are still good, but once the internals start failing like that, safety has to come first. Glad you caught it before it became a path to ground through someone's hand.

I’ve run into a few of those hot casings, but my approach ussually involves trying to preserve that heavy-duty vintage hardware if the casting itself is still solid. Those old Killark and Crouse-Hinds bodies are built so much better than the thin alloy stuff we get at the big box stores today. Last time I found a hot LB, I acutally kept the housing and just focused on a full internal overhaul. I pulled out all the old cloth-covered wire that had turned to dust and replaced it with THHN, then spent some time with a wire wheel cleaning up the ground contact points. Instead of swapping for a modern plastic or thin-gauge unit, I tapped a new 10-32 hole for a dedicated ground screw inside the original casting. It took a bit more effort than a swap, but once I had a solid bond to the equipment grounding conductor, I knew that casing woud never be a hazard again. There is something satisfying about making those old industrial pieces safe for another fifty years rather than sending all that good iron to the scrap heap.

Glad you caught that before it bit you. Those old T-slots look cool but they're a nightmare for wire capacity. Whenever I run into a hot enclosure like that, I don't just check the hot—I’m looking at the bonding bushings immediatly. People forget that on those heavy cast iron runs, if you don't have a solid bite into the hub, your ground path is toast. I ussually swap out the old fiber washers for some high-quality nylon or just go straight to a modern Hubbell 5362 if I'm replacing the outlet. That heavy-duty spec-grade stuff at least has the brass grounding strap to give you some peace of mind against the casing.

I ran into a hot LB last winter on my patio. The culprit for me was a locknut that had backed off just enugh to lose the bond. Now, I always use a wooden dowel to tuck the wires deep into the corners before screwing the plate down. It saves me from that 'crunch' feeling when the cover bites the insulation. I also make it a habit to check the exterior hub for any white crusty oxidation—ussually a sign that moisture got in and is eating your ground path. I don't even touch a metal cover anymore without waving a non-contact tester over it first.

Quick update—I took the advice to keep the original Killark body, wich defintely looks better. However, even with the new internals, I’m still getting a tiny trace voltage on the casing. I checked the bonding bushings like suggested and those were fine. Now I'm looking at the locknuts on the conduit run. Is it common for those to lose thier bite over forty years?