Stray Voltage?

I have run into this 3 times now on different RV's. In every one when the water heater breaker was turned off, no more hot skin. In all 3 the element had been dry powered and melted. The water heaters all had good grounds connected but there was still power getting to the chassis.

This is an old-wives tale I've heard for years, but which has no basis in fact. While casual observation might suggest that a melted element in a HW heater by itself can cause a hot-skin condition, in reality there must also be an open or high-impedance path in the EGC ground connection for any appreciable (more than 1 volt) to occur on the RV skin. This is my Mechanical, Electrical and Power Distro Engineering background(s) of over 40 years talking. In fact, I've set up similar experiments in my backyard using corroded and shorted HW heater elements to observe fault current and hydrogen gas production in fail mode. However, a compromised ground in an RV due to corrosion, broken ground pin, or even an missing or loose bonding screw for the G-N bond at the service panel would make it act like you describe, especially if a local ground rod alone was the only way the RV was being "grounded". In that case there will typically be 1 or 2 amperes of ground fault current flowing through the broken/shorted heater element to the chassis of the RV. This could create a hot-skin voltage and current if there was a local-only ground rod, but not with a proper EGC connection back to the service panel.

However, I know that it's hard to believe me without a real world mock-up and demonstration of the situation. This would make a great video to debunk that myth, wouldn't it? I'll see if a HW heater manufacturer who sells to the RV market will send me a hot water tank with some extra heating elements to burn up for the experiment. Do you have any suggestions of HW heater brands and models that are typical. Does the forum moderator have any manufacturer contacts they can suggest?

Mike Sokol
No~Shock~Zone