Many moons ago when I was still gourd green I found a compressor contactor with a bad coil. Found it within minutes on a Carrier package unit. Thought to self oh yeah I got this! This heating and air gig is cake! All that could be made out on the coil was a 2. No problem thought, got this on the truck. Replaced the contactor and turned the machine on. Very briefly after the contactor pulled in is when I learned the difference between 24 volt controls and 208 ! Luckily I had stepped back from the machine and when the contactor exploded none of the shrapnel hit me. Always Always Always make sure of your voltage and if your company has arc flash protection for you use it!
Those mag jumpers are an accident waiting to happen. You had a worst case scenario, but even if the thing had stuck to cabinet or the c terminal with low voltage on the other end you would have had a blown fuse or transformer (speaking from experience)
Save those for recessed terminals like on a pcb connector and be very careful connecting them. If there is anything to grab, I'd stick to alligator clips, as much of a pain as they can be.
-another tech slowly losing his green sheen
Blown control fuse, I mean
One thing I noticed right away with the MagJumpers.
Not all screws have enough ferrous material in their alloy to hold the jumper to the screw head tightly. Some screws have so little ferrous material in them that the mag jumper won't hold at all.
IMHO, be ready to be underwhelmed if you buy a set.
Thats all I need, a jumper attracted to conductive objects.