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An uninterruptible power supply, also uninterruptible power source, UPS or battery/flywheel backup, is an electrical apparatus that provides emergency power to a load when the input power source, typically mains power, fails.

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apc Back-ups cs 500 amber on battery light flashing

i just bought a ups and it is flashing the on battery light rapedly. it does this even with a battery removed. any ideas?

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1 Answer

Chosen Solution

Check your AC outlet! You have a mis-wired outlet.

APC UPS Users Manual

Point #4

Check site wiring fault indicator (rear panel-top)

A lit indicator means that a shock hazard exists due to faulty building wiring , that should be corrected by a qualified electrician.

If the building wiring fault indicator is lit, one of the following conditions exist:

• Open or high resistance ground• Hot and neutral polarity reversal• Overloaded neutral circuit

Note: Improper building wiring will not prevent the UPS from operating but will limit it's protection capability. Faulty building wiring could result in equipmentdamagethatisnotcoveredbyAPC. Please refer to APC's Equipment Protection Policy for details.”

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Power Gear 3-Wire Receptacle Tester


wall is fine


Nope! You have improperly wired outlet. You may have the issue in the fuse panel or a device which is shorted to ground.

Best to get an electrician in to service your wiring.


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