I had my TT hooked up to a 20amp gfci outlet in my garage with a Surge Guard 44260 power protector, to run the a/c and refrigerator. It was running for about an hour when I smelled something burning. I checked the power cord and noticed the surge protector was smoking from the end attached to the trailer 30 amp power cord. The 30 amp cord was also very hot but the 15 amp wall adapter was not. I have no idea why the breaker didn’t trip or what could have caused the short in the surge protector?
A bad connection or corroded plug or socket. I highly doubt if it was over the 30A rating especially since you are in a 20A outlet.
FYI, you a pushing it to run the fridge and AC on the 20A circuit but that was not an issue here.
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A burnt connection is a more common occurrence than it should be, but we see them here pretty often.
A burned connection like that doesn't increase the amperage so the breaker won't trip unless it burns badly enough to encompass the hot and neutral or ground.
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I have gotten into the habit of spreading the tangs periodically on the plug side (shore power and surge guard) and squeezing the blades on the receptacle side. (surge guard/outlet with power off!)
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As discussed here on a number of other occasions be sure to turn off the breaker before connecting your cords, and EMS units. Arcing over time, will cause the ends to burn/ corrode and eventually creat a high resistance connection causing heat. The prongs may not fail at that time, but down the road when put under heavier load. My experience with burned prongs on my adapters and cords all came under similar load situations to yours. 20 amp outlet with the AC on. If you see any heat signs on any of your cords, toss em.
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I clean the blades often, actually every other time i plug in. I carry a piece of emery cloth in my electrical bay If you continue to use a 20 amp circuit for your A/C you should periodically feel the electrical connections for heat. If you have a long run they could easily heat up.
"FYI, you a pushing it to run the fridge and AC on the 20A circuit but that was not an issue here."
Ummmm, I disagree. A PROPERLY WIRED receptacle can CONTINUOUSLY deliver ONLY 80% of its' rating (20A x 80% = 16A CONTINUOUSLY; there is supposed to be a 20% safety factor to cover BRIEF usage above the 80% rule) An air conditioner and a refrigerator together could easily exceed those 16A. Throw in the SURGE drawn when a compressor kicks in and, you have a disaster waiting to happen. Now consider that the circuit breaker has probably seen "better days" and there may well be corroded connections so, it's surprising that we don't see more overheated plugs and receptacles.
I connect my 30 amp trailer landline to a 20 amp outdoor outlet controlled by a GFCI breaker. I had one adapter that got hot after a few uses and it was on the verge of melting when I took it out of service. I run the AC while plugged in, and I will run other appliances for testing them. I always check the cord, connection and breaker for heat. I use a thermometer to do this... like what they use at the door of a doctors office when they check you. Always monitor!!!! Always !!!
Never heard of an 80% rule. I HAVE heard of a rated capacity. Also professionally speaking, for whatever reason, the connectors were not making good contact OR the connector was poorly made and the contactor and wire within cable were improperly bonded/crimped.
‘This is true. A 15 amp breaker should not carry a CONTINOUS load exceeding 12 amp. A 20 amp breaker at 16 amps etc. This is an electrical code requirement in Canada and, I might assume, also in the US. (NEC)
As has been discussed multiple times, a motor under start-up (AC unit) can see an inrush current of up to 300% over a short duration. The circuit breaker is a slow reacting device and the inrush is over such a short time, the breaker does not have time to react to the surge.
additional amp draw from converter charging batteries
The converter is also increasing the amp draw when plugged into shore power, install a battery disconnect if connected to a 20 amp circuit while running the AC, or even the microwave.
I have seen where the problem is the manufacture process. The method of how the fine strand wires are attached to the blade is a trouble spot. Some times after use, or defect in manufacturing, some of the fine wires break off where they attach to the blade. Then instead of a 30 amp connection it is reduced to a lower capacity while heating up the blade. In the case of a molded plug, there is nothing you can do!! But what I do is to buy a cap at the hardware store that screws on. Then you can form the strands and tin them, or use solder to make a solid wire for screwing to the plug. Cut one of these molded plugs apart to see the connections!
The heat is where the high resistance connection is. You clearly had a poor connection where the trailer 30 amp plug connects to the surge protector. Both parts are damaged, I cannot tell you which one started the problem. I can tell you, it had nothing to do with the 20 amp outlet you were plugged into, Again, the heat is where the poor connection is.
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I would recommend testing the breaker as well. I had one explode and start a fire in the service entrance panel when I reset it. Echo the advice to only attach plugs with the power off. Many marina fires from not bothering to do so.