UPS/SPS testing re: AC protective ground

[Neal P. Murphy]

dave at westmark.WESTMARK.COM (Dave Levenson) writes:

>In article <727 at limbic.ssdl.com>, gil at limbic.ssdl.com (Gil Kloepfer Jr.) writes:
>...
>model?   I can imagine a failure-mode in which the relay fails to
>disconnect the primary power from the load when it connects the
>secondary power to the load, but I would expect this to cause the
>whole thing to oscillate...as the secondary power would trick the
>sensor into thinking the primary power had been restored.

No, it wouldn't oscillate. The load on the rest of the grid would
suck the output voltage down to almost zero (the previously mentioned
short). The sensor would not detect a power restoration, and the
backup power would last a few seconds and probably get extremely
hot. It might oscillate if one yanked the plug from the wall, though.

NPN