At one point, when we had monitoring (simple contact closure) connected,
we were having problems with the UPS failing a battery test and
immediately sending an unnecessary shutdown signal. I solved the problem
by using a simple mechanical relay, powered by a wall-wart, that would
block the shutdown signal if line power was still on.
We eventually abandoned monitoring, because even with that relay, we
were getting unnecessary shutdowns on very brief power outages. We, too,
have redundant power supplies on our E4A, either one of which, alone, is
enough to power the box, and we have one side on UPS, the other directly
into the wall. And we have everything else that's on UPS connected to a
separate failover switch, so that there, too, BOTH the UPS AND the line
power would have fail at the same time to shut us down.
If we have a power failure during business hours, then there's usually
at least one person on the premises who can do a PWRDWNSYS if the UPS
battery gets low during a power failure, and if it happens outside of
business hours, then there's nothing going on that we can't afford to
lose if there's a protracted power failure. Plus, having one side of the
power supply on the E4A going directly into the wall means that we can
simply monitor for losing that side.