Power Transfer Switch Burning Up

[Reswest]

Hi there

New to this forum. This was where I was directed by a couple friends to get help with technical issues.

I just brought my fifth wheel back home from storage and started in on a rotten floor issue that I unfortunately discovered after purchasing the unit a year and a half ago.

Anyway....

I have the trailer plugged in to a 15 amp plug in the house directly with adapters on the heavy 50 amp cord from the trailer. I was using a heater last night to dry some floor leveling compound and had the breaker in the house trip a couple times when I overloaded the circuit trying to run anything else. Nothing tripped on the trailer panel. Not a big deal but this morning I was using my skill saw plug inside and I lost power when the heater tried to start at the same time. Went in the house but the breaker was not tripped there and I still had power at the receptical where the RV was plugged in.

The RV has a solar pannel and 4 six volts but no generator installed. I believe the switch in the attached photos is to automatically switch in between generator power and 110, but not entirely sure. I am also a little lost in terms of what all the electical “stuff” at the front compartment actually does. It does seem quite extensive compared to our other RV’s.

I did not unplug the RV cord (I know I should have!) and I heard a noise coming from the switch box and heard the microwave beap indicating the 110 power return to the RV on its own. Knowing there was an issue in the box I unplugged the trailer and took the cover off.

I could see that the white wire leading to the box was burnt at the connection and the insulation had melted back a few inches.

I would appreciate any input as to what might have caused this. Is the switch even necessary if I dont have a generator installed?

We have had the fifth wheel plugged in living in it for a couple months before without issue. That was at RV parks both on 30 and 50 amp services. I know the circuit in the house I was plugged to is quite overloaded. This may be a stupid question but could that have something to do with it. I would assume not, as something should have tripped, either at the house or in the RV.

Thank you in advance for any suugestions or input.

Gary

[wnjj]

dougrainer wrote:
A Transfer switch is just 2 to 3 relay's, nothing fancy. The OP overloaded the system and the WEAKEST point failed. Which was the loose Neutral wire. The system generates extreme heat when overloaded and the Neutral burnt due to that heat. Your post is an excellent question that most people do NOT understand----Some assume that the FEED breaker will trip and save the burning or possible fire from overloading a circuit. NO always so and not so most of the time. One of the most common causes of failure of any RV transfer switch is running more amps than the feed circuit can supply. The Heat build up causes the relay's to fail. Doug

My point was the transfer switch wire burnt because it was loose and only because of that. It could burn with half the current the OP was using. A properly wired and operating 50A capacity circuit should never overheat when supplied via a 15A curcuit.

I’m a EE and understand current, voltage, etc. Heat comes from power dissipation. The equation is i*i*R. Power is poportional to resistance and the square of the current. The thing is, a 50A transfer switch relay should have very little resistance, in fact enough that 50A squared multiplied by it won’t produce more watts than can dissipate.

So in short, the loose connection caused the burnt wire issue and nothing more. We disagree only about it being “overloaded.” The more current you run through a failing connection, the more heat you produce. Yes, a fire can start without tripping a breaker as we all know you can make plenty of heat with less than 15A. I also concur that running heavy loads in a RV through multiple adapters is the best (worst) way to find those poor connections, usually starting the the receptacle in the RV.

[time2roll]

OP was plugged into 15 amp outlet. No possible way the 50 amp transfer switch was overloaded.

[dougrainer]

A Transfer switch is just 2 to 3 relay's, nothing fancy. The OP overloaded the system and the WEAKEST point failed. Which was the loose Neutral wire. The system generates extreme heat when overloaded and the Neutral burnt due to that heat. Your post is an excellent question that most people do NOT understand----Some assume that the FEED breaker will trip and save the burning or possible fire from overloading a circuit. NO always so and not so most of the time. One of the most common causes of failure of any RV transfer switch is running more amps than the feed circuit can supply. The Heat build up causes the relay's to fail. Doug

[pianotuna]

Hi wnjj,

I've had 30 amp plugs burn on a 15 amp shore power supply. The connections were NOT loose and were tinned. The Cameco female 30 amp seem to be prone to this. The culprit appears to be voltage drop. I do treat my plugs with anti corrosion spray. The best thing to do is to keep below 80% of the shore power supply capacity.

wnjj wrote:

dougrainer wrote:
The wire burnt from being slightly loose. The REASON it did that is because you are overloading the Circuit by running too many hi amperage items with the extension cords and adapters. Doug

So you’re saying a load that doesn’t trip a 15A breaker in the house will overload a 50A transfer switch? I agree with loose connection as well as you when you say remove the transfer switch if it isn’t used. Also agree that running a saw through that many cords and adapters is asking for trouble.

[brulaz]

Thanks for the reminder.
I really should get into my electrical cabinet and re-tighten all the electrical connections. The 120VAC ones in particular.
Things can get loose when bouncing down the road.

[wnjj]

dougrainer wrote:
The wire burnt from being slightly loose. The REASON it did that is because you are overloading the Circuit by running too many hi amperage items with the extension cords and adapters. IF you are NOT going to ever install a Genset, just remove the Transfer box and connect the Shore Power wires to the Power cord wires in a standard 120 electrical box. No need for a Transfer box if you do not have a Genset. Doug

So you’re saying a load that doesn’t trip a 15A breaker in the house will overload a 50A transfer switch? I agree with loose connection as well as you when you say remove the transfer switch if it isn’t used. Also agree that running a saw through that many cords and adapters is asking for trouble.

[pianotuna]

Monitor the voltage. Do not transfer power "under load". I hate automatic transfer switches.

[dougrainer]

The wire burnt from being slightly loose. The REASON it did that is because you are overloading the Circuit by running too many hi amperage items with the extension cords and adapters. IF you are NOT going to ever install a Genset, just remove the Transfer box and connect the Shore Power wires to the Power cord wires in a standard 120 electrical box. No need for a Transfer box if you do not have a Genset. Doug

[wildtoad]

Perhaps related, Newmar (not your unit) has a recall on transfer switches in some of the gas models due to loose connections causing heat to build and possibly a fire. So my take is loose connections could have been the cause. BUT quit doing what you’re doing and install a 30 or 50 amp circuit.

A few years back, I hooked my 30 amp MH into a 15 amp socket in a outbuilding installed by a previous owner, and was running the AC, and a vacuum cleaner. At some point it quit, and after looking found melted wires in the storage shed.

[Boon_Docker]

As mentioned above a loose connection will cause arcing and the wire at that point will heat up extremely.

[DrewE]

Mandalay Parr wrote:
The connection was probably not screwed down tight.

x2; this is the most likely cause, in my estimation. Fix it (and replace the overheated piece of wire at the same time). If the transfer switch itself shows signs of overheating, like discoloration or melted/blackended plastic bits, it would be wise to replace it or at least those components if they're individually replaceable...or eliminate it.

Some sort of a transfer switch is needed whenever you want to feed the same circuit from two different power sources (at different times)--in this case, from the shore power cord and from either a generator you don't have or perhaps from an inverter. If it's wired to a generator you don't have, and you do not foresee installing a generator, it would be perfectly reasonable to eliminate the transfer switch entirely.

Overloading your 20A supply, while a bad practice, would not have caused this particular failure.

[MrWizard]

deleted

answered the wrong question

[time2roll]

Just a loose wire. Yes if the second input is unused you can replace or bypass the transfer switch. You still need to make good connections and remove the burnt wire.

[Mandalay_Parr]

The connection was probably not screwed down tight.