The up-time isn't linear; half the load will give more than twice the run-time. Rule of thumb is about 5 minutes minimum for a fully loaded UPS, and about 15 for half-load. Long enough to get the generators up and running, and not much more! But as NJwirenut says, it varies wildly from UPS to UPS and use to use. Know the precise draw of the X-Ray equipment would be crucial to a good estimate; for the price they'll pay for 2000+VA UPS, it's worth it to stick a clamp on for a bit so you don't overspend or underestimate.

Also, don't forget to factor the charging circuit of the UPS in, too! If you suspect those two boxes are drawing 14.5A on a 15A circuit, two UPSs on there charging batteries will push it right over the top. I've spoken to engineers at APC who have stated all their Smart-UPS draw 1A while charging. I asked specifically regarding the SmartUPS 1500 and 700, but they said the while line draws 1A while charging. I assume they meant only up through 2000VA or so, as the 15kVA and others certainly draw more!

[This message has been edited by SteveFehr (edited 04-11-2005).]

[This message has been edited by SteveFehr (edited 04-11-2005).]