Posts Tagged ‘circuit breaker trips’

Circuit Breaker Trips and UPS Dies

July 21st, 2009 Comments off

MIDWEST was asked by a maintenance foreman “why his computer went off’ even though it was on a UPS when they lost power.  He said they had a brand new circuit breaker trip and within a couple minutes his computer went blank.  His UPS just died the first time he needed it.  When we asked why the new circuit breaker tripped, he just smiled and said “OE.”  OE (Operator Error) usually means “We know why but don’t want to say, so don’t ask any more questions.”  Used, obsolete, General Electric, Westinghouse, Square D, Cutler Hammer, used, obsolete, and even new circuit breakers by any mfg. are not designed to protect you from OE.


We explained that a small UPS on a single computer usually is sized to provide power long enough to “save” whatever you are working on and then “shut down” your computer properly so you don’t lose anything.  The UPS also keeps the computer on if you have a brief outage of a few seconds because of things like a storm or utility switching.  The UPS on my computer will keep the computer and monitor and small light on for 12 minutes.  Yes, we’re Engineers, so we actually tested it. Twelve minutes and 27 seconds, to be precise.  Here’s a big tip!  Plug the monitor into the UPS also.  It is not easy to properly shut your computer off when the monitor is blank.  And if you don’t have an office window, we suggest adding a small desk lamp to the UPS.  But a small UPS on a single computer is not designed to outlast OE.


Larger UPS systems will provide more power or power for a longer time.  In any case, UPS systems are only a temporary source of power to critical equipment or to safety equipment.  Sometimes a UPS is used in conjunction with an automatic transfer switch.  The “Automatic Transfer Switch” (ATS) transfers a circuit or panel of circuit breakers from the normal power source to another power source or generator. When an ATS switches, there is a momentary power loss, so computers will still shut down, unless there is a UPS on the computer to provide power for that fraction of a second it takes the ATS to switch from one circuit to another. 


The maintenance foreman’s UPS worked properly.  He didn’t realize the UPS would provide backup power for only a few minutes.