At an inspection today I had a microwave that didn’t work. When I checked the upper outlet on the duplex plug, it showed reverse polarity. I unplugged the microwave to double check that half and it read normal. Rechecked the upper outlet and it now read normal. As soon as I plugged the microwave back in, it flipped to reverse polarity. Obviously the microwave is bad, no power at all, but how would it cause the tester to read this way?
I’m not sure that the microwave is part the problem. You would need to pull out the receptacle and see if it was wired correctly as well as test the conductors in the box. I would also plug the microwave into a known working receptacle to test it.
Your three-light “tester” is not sophisticated enough to give you a proper diagnosis.
How about a receptacle testing Hot/Ground Reverse and when light is turned on, testing polarity reverse…
Still not an accurate assessment. There is a wiring issue, but there’s no way to accurately diagnose it through the use of these devices.
I had this happen to me a few years ago. when I pulled the receptacle I found that the ground was bootlegged. That is what went into my report. If your 3 light tester is acting peculiar, it is always best practice to pull the receptacle and see what is going on.
Likely something is going on with the receptacle but it may not be what the 3-light tester says it is.
There is a thread somewhere on this site where three light testers were discussed in detail. They will indicate a problem but does not always accurately interpret what the problem is.