Originally Posted by Vern
I asked myself "how could I have 'reverse polarity' one minute and not the next?"
Easy. But first one must understand how reverse polarity is detected.
To appliances, polarity is irrelevant since both hot (black) and whilte (neutral) wires constantly reverse polarity. Polarity is simply another layer of human protection. Polarity is determined by measuring voltage between those two wires and the safety ground.
So what voltage constitutes a reverse polarity? Normally safety ground and neutral are exactly same with no load and a few volts difference with a load. Reverse polarity is determined, for example, by a higher voltage difference. A failing or undersized neutral incoming to the pole might explain it. Or some problem with the pole's earth ground such as not fully conductive or, for some reason, is carrying current. (Earth ground and safety ground are electrically different.)
You know that reverse neutral was reported due to changing voltages. Many different voltages exist simultaneously on the same AC service - not just 120 VAC. That design of surge protector was apparently detecting one of those other voltage changes which, to a better informed electrician, implies something is slowly getting worse in local power districtuion.
Reverse polarity does not threaten appliances. It is simply one layer of human protecxtion that has been compromised.