I have wondered about this also. If you run it at full load it could be a
problem. At say half load or less it should be safe unless the vendor is
really pushing the semiconductors past there limits. In this case you
should not be using the thing for and UPS anyway.
The best thing to do is test it. Run the UPS for a while and see what
gets hot.
As long and the parts don't get so hot that you cannot keep your finger
on them for at least a few seconds you are ok. Don't do anything stupid!
There are LETHAL voltages in the UPS. Probe around with a meter before
you stick you hands in there and keep one hand in your pocket when you
do just in case.
Please note the average human finger can only be held on and 55 degree C
object for about 3 or 4 seconds. Most devices are safe to operate at this
temperature for long periods of time.
A temperature probe is the best way to do this test of course.
Mike Duvall
ac4zq