I took post 3 by BisyB as an update to the voltage readings.

EDIT - Check that, read it as 208.7 volts not 228.7. Time to call it a day and watch some March Madness games.

I do trust fluke meters, even if I don't have one in my bag (yet). I would be curious what he finds in the power system as he starts moving closer to the service transformer outside.

In that case, have him check the battery.

Sixteen minutes after I started this thread, KOT called it:



Details, just as a reminder:

When my friend got the electrician on site and showed him the measurements, he said "that's how it is in Mexico."

My friend is troubleshooting and improving that system for another installer, who didn't think to measure the supposed 120V power and was unaware that he was slowly cooking components from the inside. They're going to switch the entire system to balanced power anyway (transformers made by Torus). The transformers for that are custom and will be built to output 120V.

Thanks for all your suggestions. Who woulda thought the stupidest answer would be the fact of the situation?