I install and repair coffee and espresso equipment and we sometimes run into electrical problems beyond my knowledge (well versed in household wiring, good with fundamental applications of ohms law, etc. but I'm no physics major!) The issue that comes up most often is dubious grounds, or occasionally neutrals. If there's a loose wire-nut connection, a partially broken wire with one thin strand left, or a very poor connection in a breaker box, I could get good multimeter readings from the building wiring going into a coffee brewer (120vac from each of the two hot legs to ground and to neutral, 240 between them (or 208 if feeding from three phase power), and 0 voltage from neutral to ground... but that thin/loose/weak connection wouldn't be able to carry the current necessary for the machine to operate safely and properly. So my question is, what can I do, beyond the multimeter testing I just described, to try to root out wiring that's not completely mis-wired or disconnected, but simply undersized or poorly connected? If it helps at all, the most recent issue to make me wonder about this is a large (240vac, 25amp, brews up to 3 gallons at a time) coffee brewer at a hotel which had run fine for years until it's main circuit board caught fire. We didn't have a replacement board, but had a spare machine, so we installed a different machine (eliminating the likelihood that any problems with internal wiring of the machine could be the culprit), which subsequently blew up its main circuit board within 24 hours. At that point, I checked and re-checked the wiring to the best of my ability and hoped that it was a terribly unlikely coincidence... and installed a new circuit board, which caught fire within about 2 hours of being hooked up! If the neutral wasn't acting like a proper neutral, the relay and a few triacs on the board could see way higher voltages than they expect, which might explain the meltdowns, but I don't know how to find the wiring problem. Sorry for the long first post. I'd greatly appreciate any insights into testing neutral and ground wiring.