12v master Reset Breaker --- typical causes for tripping?

[SJ-Chris]

This is on a 2015 Thor Majestic 28a Class C RV.

On the control panel, there is a light to show that the 12v Reset Breaker has been tripped. Looks like this:



I believe this is a master 12v breaker that goes to the fuse box. Thankfully, it hasn't given me much trouble over the years. I've got two of these RVs and it has only tripped twice in 3 years. One of those times was today while a friend was using my RV. I told him how to reset it. Underneath the dinette seat where the fuse box and converter are, there is the breaker. It looks like this:



He pushed the button and reset it and all seems fine now. But I'm a bit of a perfectionist and I don't like when things like that happen and I'd like to know "why". I asked him what was happening electrically when the breaker tripped. He said he was unplugging from shore power when it happened. He said he first turned off the camp power pedestal breaker, then unplugged the RV from the pedestal, then he plugged the plug into the generator outlet junction box (generator was off) as he put the cord back into the side compartment. When he went back into the RV the master Reset Breaker light was on as it had tripped.

I believe the AC was not on (too cold outside), the microwave was not on, the water pump was not on. This RV has two 12v RV/Marine batteries that are in good shape and fully charged. This RV has 500w of solar along with a 2000w inverter that goes to two outlets in the RV. The inverter might have been on, but nothing was plugged into the inverter outlets when the reset breaker tripped.

Any thoughts as to what could have caused this?

Thanks in advance!
Chris

[pianotuna]

Chris,

I deliberately tested the RV by turning on everything. It did cause the 40 amp breaker to trip.

I've never had a repeat.

The charging wires for the "house" battery bank came with a "hard to find" 60 amp blade fuse.

I upgraded adding a 2nd charging path with #8 wire (oem is #8) and added two 50 amp auto-reset breakers. The meter I have maxes out at 70 amps--and I've had occasion to see it drop to zero as the auto reset connects and disconnects. I have manual control over the charging solenoids, which are rated at 200 amps, contacting. The oem solenoid had burned contacts.

I've now moved to a 20 amp dc to DC charger for the "house bank" using the starter battery to feed the house bank. I chose 20 amps based on the size and duty cycle of the alternator.

[SJ-Chris]

stevenal wrote:
A manual reset CB will open during an overload or short circuit. One can then investigate the cause and adjust the load or repair the short before resetting the cb. An automotive auto resetting cb on the other hand will alternataly open and close on this overloaded or shorted circuit until someone intervenes, the load drops by itself, or the circuit burns open. I find the auto resetting automotive cb to be a bad idea in general, and a particulary bad idea in a residence.

Thanks for your feedback. I guess I'd like to hear/learn more about the potential dangers of using an auto-resetting breaker. Anyone else care to comment? If they were dangerous, would they use them in autos/RV???

I did find this very interesting video. Shows a cutaway of an auto-reset breaker in action.

https://www.youtube.com/watch?v=lt4R-G46quc&t=98s

In my case, the manual master reset breaker has tripped very rarely (and then went back to normal operation when reset manually)
I feel an auto reset breaker would be low risk in my scenario to date. But if there was a true short/etc that continually tripped the auto reset breaker what would be the likely outcome?

[stevenal]

A manual reset CB will open during an overload or short circuit. One can then investigate the cause and adjust the load or repair the short before resetting the cb. An automotive auto resetting cb on the other hand will alternataly open and close on this overloaded or shorted circuit until someone intervenes, the load drops by itself, or the circuit burns open. I find the auto resetting automotive cb to be a bad idea in general, and a particulary bad idea in a residence.

[SJ-Chris]

pianotuna wrote:
Chris,

Replace any incandescent lights with led's.

I deliberately tested the RV by turning on everything. It did cause the 40 amp breaker to trip.

I've never had a repeat.

LED lights are one of the first mods I do on any new RV! Yes, they use MUCH less power. This RV has LED lights.

Just a random occurrence (tripped reset breaker) that has only happened twice in 3 years. I have ordered auto resetting breakers and will replace in all my RVs (an inexpensive and easy switch).

Thanks for the suggestions!

-Chris

[wa8yxm]

pianotuna wrote:
Chris,

Replace any incandescent lights with led's.

Excellent suggestion breaker issues or not.

A 1136 lamp is 19 watts or about 1.5 amps give or take a bit depending on voltage. The LED equivlent... closer to 0.15 amps.

[pianotuna]

Chris,

Replace any incandescent lights with led's.

I deliberately tested the RV by turning on everything. It did cause the 40 amp breaker to trip.

I've never had a repeat.

The charging wires for the "house" battery bank came with a "hard to find" 60 amp blade fuse.

I upgraded adding a 2nd charging path with #8 wire (oem is #8) and added two 50 amp auto-reset breakers. The meter I have maxes out at 70 amps--and I've had occasion to see it drop to zero as the auto reset connects and disconnects. I have manual control over the charging solenoids, which are rated at 200 amps, contacting. The oem solenoid had burned contacts.

I've now moved to a 20 amp dc to DC charger for the "house bank" using the starter battery to feed the house bank. I chose 20 amps based on the size and duty cycle of the alternator.

[SJ-Chris]

dougrainer wrote:
That is a 12 volt breaker. NO 120 appliance will cause the overload to trip. Also a short in the DC supply to that breaker will trip it. I do NOT like manual reset breakers. I would replace with a auto reset breaker of the same amp. Transient things in RV's cause fuses and these type breakers to trip. With an Auto reset, once the overload or short goes away it resets. Both Auto and Manual reset breakers can wear out over time if they continually trip. Doug

Auto-reset....great suggestion! And the location/etc would make that a simple change to make. AND it looks like auto-reset breakers are inexpensive.

From documentation I found online for my RV, looks like this is a 40a breaker. I think I'll buy these and install them.

https://www.amazon.com/Ampper-DC-12V-Automatic-Automotive/dp/B07W98CCNK

This way, if it trips on rare occasion for some non-frequent surge/blip, it will simply reset and nobody will be bothered.

Of course if it trips and doesn't reset, it would then be highlighting an actual problem.

Thanks,
Chris

[wa8yxm]

There are typically 3 or 4 things that trip a breaker

OVER CURRENT.. Well that's what is supposed to trip them
Vibration (I mean VIBRATION!!!!!!!) generally this only applies to a generator at shutdown or perhaps washboard alley.
Some do not like very high temperature environments. (Do not think that was the cause we are talking close to boiling here). (May be caused by bad connection)

And last.. this will cause FREQUENT tripping, not once every year or so.
Defective breaker. I had that happen to me a few times at campgrounds with the campground main 120 volt breakers.

[dougrainer]

That is a 12 volt breaker. NO 120 appliance will cause the overload to trip. Also a short in the DC supply to that breaker will trip it. I do NOT like manual reset breakers. I would replace with a auto reset breaker of the same amp. Transient things in RV's cause fuses and these type breakers to trip. With an Auto reset, once the overload or short goes away it resets. Both Auto and Manual reset breakers can wear out over time if they continually trip. Doug