Originally Posted by rogerkathy
I guess I better check ALL my house outlets.
Appreciate what was discovered. Polarity is one of many 'layers' for human protection. Polarity is irrelevant to appliance protection; is only one of many features for human protection.
Other human safety defects can exist - a three light tester cannot detect them.
Back to the camper. Some (first) faults will not be apparent when using a meter. Others become apparent after drawing power from a pedestal. A properly designed protector will not connect power until first checking for those (first) faults. And will continue checking when other (second) faults can be detected - after a camper draws power. Checking (ie with a meter) before connecting power dies not detect all anomalies since some may only be apparent after a camper consumes power.
Best protector disconnects when either (first or second) anomaly is detected. Meter only detects a fault. As oldtool2 so accurately notes, human cannot disconnect fast enough.
Cost should always be secondary to solving an unacceptable problem Especially when a properly designed protector is so inexpensive.