Another 3-light tester failure!

What can cause a 3-light outlet tester or surge protector to randomly indicate reverse polarity?

Everyone,

I’ve occasionally had readers send me questions about a strange phenomenon at campgrounds where a surge protector first indicates that the pedestal wiring is correct, but sometime later it shows reverse polarity.

Review how 3-light outlet testers and surge protector indicator lights work HERE.

How I first discovered this error condition…

I remember observing this strange error condition some 20 years ago when I was studying what causes a hot-microphone voltage on music stages. Here’s my portable live-sound shock and hum demonstration gear which lets me induce hot-mic voltage or ground-loop current into sound systems.

Random reverse-polarity indication at a campground pedestal can be caused by a reflected hot-skin voltage!

Watch this important 4-minute video about hot-ground voltage below.

What is a Reflected Hot-Skin Voltage?

This is a bit tricky to understand, but it happens more than you might think. In a campground, the feeder conductors typically daisy-chain from pedestal to pedestal, fed by a common circuit breaker in the main service panel. If there’s an interruption in the grounding conductor path back to the service panel bonding point for any reason (corroded or loose connection in one of the pedestals, a broken wire underground, or even a disconnect of the bond to the neutral in the service panel), all RVs that are downstream of the ground break will have their chassis connected together, but none of them will be grounded (bonded) to the main service panel.

All for one, and one for all…

So, in that case, if a single RV has something like a fried electric element in the water heater, without proper grounding that 1 or 2 amps of fault current can easily turn into 80 to 120 volts of hot-skin potential. And that same voltage can be “reflected” to the other 6 or so pedestals on that group. So, if one RV has a fault current that turns into a hot-skin voltage, all the other RVs in the area can have the same hot-skin voltage if there’s no service panel ground bond.

Final Analysis

If you’re at a campground and the surge protector or 3-light tester indicates correct wiring one day and reverse polarity wiring later, it’s likely caused by a reflected hot-skin voltage that’s changing from another RV’s leakage current.

Time to get out your meter and check the voltage between your RV chassis and earth ground. Read my in-depth article about troubleshooting hot-skin voltage conditions HERE.

If your RV measures more than a few volts AC between chassis and earth ground, then you need to make the campground staff aware of a potential failed ground connection in that group of pedestals. Don’t delay since this could be a very dangerous condition.

Let’s play safe out there… Mike