AND NOW AN irritating story from the old days
In the 90s I worked for a Motorola outfit, and installed E911 telco/ radio gear. Down in Ritzville, WA the SO had bought a new UPS. Took two big golf cart sized 6V batteries. it was 3 phase 240AC. The electrician wired it up, and it had a bypass switch for servicing. BEAR IN MIND this is a special switch. As you move the switch, in the middle of it's "throw" it CONNECTS the UPS output to the line power for a short time, before it "breaks." This bypasses the UPS so it's "dead" for service, and so that power is not glitched in doing so. Bear in mind the UPS output and the line power MUST be in perfect phase at this moment.
The electrician asked me to look it over and be certain he had not made a mistake, and then we "tested" it
Ker FREEKIN BLAMBO!!!! Smoke!!! Sparks!!!! NOISE!!!! FAIL!!!!! Turns out he HAD wired it correctly, there was something wrong with the way the UPS itself was configured. The company did not argue, they came out and repaired the UPSw
