Emerson 250-400kVA Manuel D’Utilisation

If a problem occurs within the UPS, review all alarm messages along with other pertinent data. Con-

tact Liebert Services at 1-800-LIEBERT to report a problem or to request assistance.

For each alarm message on the Display Screen, you can find the recommended corrective action in 
Table 7.

During normal UPS operations, short-term overload current demand from the bypass source may 

reach 10 times the UPS output current rating. This overload current demand may be caused by the 

magnetizing inrush current of one or more downstream transformers (i.e., power distribution units) 

or faults on downstream branch circuits. The instantaneous trip point(s) of the upstream bypass 

feeder breaker(s) must be set to support these temporary overloads. The magnitude of short-term 

overload bypass current demand is typically six to eight times the UPS current rating, but must be 

determined by analysis on a per-site basis. This analysis, generally known as an End-to-End Fault 

Coordination Study, must be done by a registered professional engineer experienced in this activity 

and familiar with local codes and related requirements.
Liebert strongly recommends periodic inspections of the bypass feeder breaker instantaneous trip set-

tings, as well as the module input (rectifier) feeder breaker trip settings, to ensure that they are cor-

rect. For a variety of reasons, although typically during circuit breaker maintenance procedures by 

others, trip settings have been known to be inadvertently left improperly set. Correct trip setting of 

these circuit breakers is most important to achieving high-availability from your Liebert UPS system. 

For further information regarding proper trip settings for your feeder breakers, call 1-800-LIEBERT.

NOTE
The instantaneous trip setting of the breaker feeding the UPS bypass input should be high 

NOTE
While Liebert can provide typical guidelines, the responsibility for the proper breaker trip