Originally Posted by Neoteny
This is for two theatres that do not have backup, and with the current building works they wanted a temporary measure in place IF the power fails.
Even the Nightingale hospitals fully meet the requirements set out in BS 7671 section 710 (IEC 60364-7-710). You can't mitigate away the requirements for the electrical installations in medical locations by "sticking a UPS" onto a medical device!

Also remember you are creating (or modifying) a ME System. This is not just an electrical safety issue (leakage current, EMC, etc.) but a design change. Will the UPS handle the inrush current, can you start up the UPS without a mains input, what happens if the UPS overloads, etc.

My advice, as Geoff said, step away and pass this upwards!