Here is a question from a site visitor regarding a melted adapter plug for his R.V. supply cord.
The other day I went out to my R.V. to check how it had survived the winter, and to begin getting it ready for the up-coming start to the camping season. I found the batteries completely dis-charged, and the breaker that feeds the outdoor receptacle was tripped. Upon further inspection, the 125V / 30A to 125V / 15A adapter had obviously got very hot as it was melted and now rendered useless. I keep it plugged in to ensure the batteries stay charged and don’t freeze over winter. However I noticed that I forgot to turn the thermostat off, and had left in on the ‘cool’ setting. When the spring sun warmed the unit up inside I am guessing that air-conditioning kicked in and that’s what caused the plug to melt and the breaker to trip. My question is that why the breaker wouldn’t have tripped before the adapter got hot enough to melt?
It is a good idea to keep an R.V. plugged in over winter as fully charged battery or batteries won’t freeze. However, make sure that your R.V. electrical system incorporates ‘smart’ technology to avoid over-charging and eventually boiling the batteries dry, damaging them beyond repair. This is only a problem in older units so check your user manual to see what they recommend for winter or extended storage.
As you pointed out, your mistake was not disabling all unessential electrical loads. When you use adapters you need to ensure that you keep your electrical usage to a minimum. Here is a great article that talks about this topic in detail.
As for why the breaker didn’t trip, that is likely due to a fault with the breaker itself. The main function of a circuit breaker is to trip on a short circuit, where thousands of amps flow instantaneously. The secondary function is to trip on over-current, and the accuracy of breakers tripping on the rated current depends on the manufacturer of the breaker, the length of time that the breaker is in an over-load situation, or a problem with the individual breaker in question, etc. For example, some 15A breakers may trip at 14 amps, some may hold in for a while at 30 amps. If your breaker held in for a while at 30A while trying to run the air-conditioner, this would be enough to heat up the adapter and cause the heat damage to it.
If you are leaving your R.V. plugged in for an extended period of time, make sure you shut off the breakers inside the unit to all un-essential loads, and check the unit regularly throughout the winter to ensure that everything is OK. That way it will be ready to go when the camping season begins, and you can get out and enjoy all that spring and summer has to offer!