Site wire fault detectors

[electronics-whiz]

I was testing a UPS unit the other day. Part of the test was the buck, boost circuitry. I used a variac to change the input voltage. I noticed plugged unit in wall the wire fault light was out, when I set the variac to 120 and tried it was on. Variac, output socket is all grounded and to my knowledge is wired right.

I don't get why the variac would trigger this light. I don't know how this type detection system works either. Only thing I can think is that because the variac has hot and neutral that maybe somehow it is sensing an issue because connection between hot and neutral in the variac.

[ConKbot]

Make sure your variac is wired correctly, N to N, G to G with a good low impedance between them (sub ohm).  If it was wired incorrectly (a 5 terminal variac, for example, could be mistakenly wired wrong) it could appear to work normally, but if you measured neutral to ground with it on, you may see some voltage, which would trigger the site wiring fault light.