Re: UPS and power shenanigans...
>I can tell you for a solid fact that APC UPS units get mighty peeved when they see 220 on the _ground line_.
What, it's 2017 and this is still a problem! :)
Back in the late 1970's I worked for a company that installed IT systems next to railway lines ie. signalling systems. Where fluctuating voltages on the ground line were regular events (ie. every time a train went by). So the company had developed some rather fancy switch gear that sorted the problem. The other problem (to delicate IT systems) we saw in the early 80's were the power spikes caused by the then newly introduced thyristor controlled systems, these were particularly troublesome as they were invisible to the then new digital scopes but not to the analogue scopes.