[BC] UPS Hell

[Mike McCarthy]

On 2/22/2012 11:44 PM, Clay Freinwald wrote:
>Entercom here in Seattle has a UPS Transfer switch around every one of their UPS's .
>
>I too have made these using an 8 x 8 plastic box (From Lowes).   I had a bunch of 120 V relays.   Purchased some short extension cords, b

All due respect, this is a dangerous practice.  I can't tell you how many seized contactor's and relays I've seen in industrial applications where switching loads was necessary.  Especially if only switching 208 or 240V.  What happens when one hot seizes closed one way and the other pole switches.  If they're not in the phase, you have a fault condition and tripping breakers (hopefully)

UL spec as I recall for autoswitching calls for three relays with an interlocked design to insure that both supply sides can't be closed at the same time.

We looked at auto-switching our new whole studio UPS system and it was ungodly expensive....and rolling our own wasn't a viable option.

MM