Whenever I exercise my building generator feeding the optional stand by system the commercial 60 three phase breaker trips when the transfer switch switches back to commercial power. When we reset it it holds just fine. The load is only about 40 amps. But, it feeds a 30 KVA three phase UPS first. Does the UPS have a large in rush?
Breaker Tripping on Transfer to Emergency Power
- Thread starter JdoubleU
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petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
The UPS might have a large enough inrush to trip a breaker but one would think it would have been charged from the generator so it should be fully charged. How long is it taking to trip after the switch occurs.
texie
Senior Member
- Location
- Fort Collins, Colorado
- Occupation
- Electrician, Contractor, Inspector
Yes, I would agree. Depending on the ATS he may be limited on options, but if nothing else, hopefully there is there are settings to put a few seconds of delay between sources.
Originally Posted by meternerd
You could be transferring out of phase. Your switch may have a synch-check feature. There's usually a switch or software setting that enables this feature. It should be enabled.
About 15 years I ran into the same situation. The UPS was a Liebert and the ATS a Russelelectric.
The ATS did not have a 'synch-check feature', you spoke of. Russelectric did have an add on kit that delayed, slightly paused, the motor action of the transfer switch after contact break to contact make of the switch mechanism. It solved the problem.
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