Why do I measure voltage on the outputs of my UPS even though the output is turned off? Why do I measure voltage on the input when the UPS is on battery?

Search FAQs

Issue:

Why do I measure voltage on the outputs of my UPS even though the output is turned off?
Why do I measure voltage on the input when the UPS is on battery?

Product Line:

Smart-UPS

Environment:

All models, All Serial Numbers

Cause:

Phantom voltage can sometimes be detected with a voltmeter on the output of the UPS even though the UPS output is switched off.
This voltage is not actually present, and If a resistive load (such as an incandescent lightbulb) were to be applied, the voltage will immediately collapse.
This behavior is normal and to be expected.

This same phenomenon can be seen on the input of a UPS when it is on battery. This would also collapse if any load were to be applied. All Smart-UPS incorporate backfeed protection and meet UL specifications for such.

Resolution:

This is normal operation and will not affect any equipment connected to the UPS.