Water Heater and 120v Problems

It isn't as if I didn't know better, but somehow when winterizing my trailer and draining the water heater last Fall, I was rushed at the time and forgot to flip either the breaker or the outside panel on/off rocker switch for the RPod's electric water heater.

Of course when I plugged the trailer in to top up the battery and run some lights and a little radiator mid-winter, the water heater was dry and the heater element was energized and unknown to me at the time promptly burned out, which I only discovered last week when de-winterizing.  The other 120v power in the trailer was unaffected, and the water heater 120v breaker in the RPod did not trip off.  What I guess happens is the coil just gets very hot then cracks and the current stops running through it, without any short out.

BUT - a secondary effect that had me scratching my head for a while - after I had refilled the hot water tank but before the penny dropped and I realized the heater element was burned out, the trailer was impossible to power-up with 120v shore power to a GFI plug outside my home.  Plug in, power would snap off instantly at the plug breaker.  Mystery deepened when I methodically turned off all the 120v breakers in the RPod - and still could not plug in without tripping the GFI plug at the house.  Not happy because of course I now couldn't even charge up my 12v battery, and non of the electrics worked.

I was wondering, had my 30 amp cable developed a fault?  When I had washed the trailer had water seeped into the A/C or Fridge vents and somehow was sorting the whole 120v system?  Was it damp in the extension cord I was using? 

Then some internet research and an AH HA! moment.  By now even though I had no power I saw that the water heater switch had been left on along with the breaker so I assumed I had burned out my element. 

The 120v system failure was coincident with filling the water heater, even though with it now turned off at both the switch and the breaker power was still tripping off at the shore plug.  Turns out modern GFI plugs have two failure sensor circuits - one for the hot power circuit, of course, but the other is for the neutral circuit, which is unswitched.  So the water in the tank, I was guessing, was completing a neutral to ground circuit in some very small voltage or amperage (ie. tiny) but that was still enough for the clever GFI plug to sense a fault and immediately trip.  Safety first.  I could have plugged into a non-GFI plug to test my theory but was afraid if I was wrong I might be frying a short elsewhere in the hot circuits and might do a whole lot of damage to my power main in the trailer.

I was sweating bullets about some mysterious power problem that was going to be a repair nightmare as I replaced the water heater element and crossed my fingers I could now plug in the trailer.  Ta da!  All problems solved.  Total cost of my mistake about $20 and a whole lot of unnecessary worry.

So if you have a mysterious complete inability to plug in without tripping a shore power breaker or GFI plug - the prime suspect may be your water heater element with a fault in the neutral circuit.

BTW - Check out YouTube "RV Water Heater Element Replacement" or similar and there are lots of easy to follow videos on the easy-peasy self-fix for replacing the element on a Suburban brand RV water heater.  I did it and am no mechanical genius, just a screwdriver and wrench job and about 20 minutes.  About $10 for the replacement 1440w/120v standard screw-in water heater element available at almost any hardware store, and a one-time purchase of a heater element wrench if you don't own one for another $10 or so - it looks just like a sparkplug socket on steroids, and is necessary to grasp the large hex collar that is used to screw the heater element in and out.

That's all it took me to learn 

Wow, good to know, thanks for sharing this.