UPS Behavior

[augie47]

I have one of those situations where one thinks witchcraft is involved.
For conversation sake, a UPS systems is fed by a branch circuit in Panel A, a building subpanel, and feeds a subpanel UP. If one turns off the branch circuit breaker in panel A feeding the UPS, the UPS performs as it is designed. If the facility looses utility power to MDP, or the main breaker on MDP is turned off, the UPS does not switch on.
(The UPS is fed by 208, single phase L1, L2 & Gr and has a 120/240 output L1-N-L2, Gr)

Any ideas ?

 

[zbang]

For conversation sake, a UPS systems is fed by a branch circuit in Panel A, a building subpanel, and feeds a subpanel UP. If one turns off the branch circuit breaker in panel A feeding the UPS, the UPS performs as it is designed. If the facility looses utility power to MDP, or the main breaker on MDP is turned off, the UPS does not switch on.

Does the UPS have a static or mechanical bypass line? If so-
When you turn off the breaker in panel A, does the bypass line still have power?
Is the bypass input carrying current when the UPS inverter should be?
(Or the simple test, albeit nonconclusive- when you turn off the panel A breaker, does the sound of the UPS change markedly? Most newer UPSs make substantially more noise when actually supplying the load.)

I'd check around with a meter to see which input and output lines are carrying current. If the outout is delivering 30a while the main input is only carrying 5a, that 25a has to come from somewhere.

If no bypass- is panel UP -really- supplied by the UPS?

z!