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SJ-Chris · 11-19-2022, 03:06 PM

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

twinboat · 11-19-2022, 03:46 PM

The inverter or any 120 volt items wouldn't be wired thru that breaker. Only 12 volt house loads.

Do you have a slide in that rig ? Could be a breaker for that.

SJ-Chris · 11-19-2022, 03:57 PM

Quote:

Originally Posted by twinboat

The inverter or any 120 volt items wouldn't be wired thru that breaker. Only 12 volt house loads.

Do you have a slide in that rig ? Could be a breaker for that.

There is no slide on this RV.

That breaker is for all 12v for the RV. When it trips, none of the 12v items work.

Just trying to find some of the usual causes for it to trip.

It seems to have happened this time when someone unplugged from shore power. Just thinking out loud.... When plugged in to shore power, the converter should be supplying all 12v power (right??). Then when the shore power is unplugged, the converter stops providing 12v power and the coach batteries take over. Could there be some sort of blip or surge when this transition takes place?

Like I said, it has only happened twice in 3 years. Thus far I would say it's not a big issue. I just like to understand "why" it might be happening so that I might be able to cut off future problems from developing.

Thanks!
Chris

Jon_C · 11-19-2022, 05:37 PM

Typical cause for trip would be any load or short that pulls more current than the rating of the breaker.

Do you have anything that can pull more than the breaker is rated for?

Neither the breaker or wiring in pic looks anywhere near big enough to power a 2000w inverter, if so that could be the problem.

Unplugging from shore should not Cause it to trip, everything is connected to battery all the time, when you unplug, the battery voltage just drops a little bit due to not being charged.

My guess is the breaker has gotten weak and needs to be replaced.

SJ-Chris · 11-20-2022, 11:56 AM

Quote:

Originally Posted by Jon_C

Typical cause for trip would be any load or short that pulls more current than the rating of the breaker.

Do you have anything that can pull more than the breaker is rated for?

My impression is there isn't much load on the overall system when this happened. Just a family in the RV doing normal stuff. Just the 2nd time in 3 years and there wasn't a good explanation for the other time either. I guess my plan is to just replace with a self resetting breaker.

Quote:

Originally Posted by Jon_C

Neither the breaker or wiring in pic looks anywhere near big enough to power a 2000w inverter, if so that could be the problem.

The inverter is connected directly to the batteries and has it's own fuse.

-Chris

CharlesinGA · 11-20-2022, 09:06 PM

Quote:

Originally Posted by SJ-Chris

My impression is there isn't much load on the overall system when this happened. Just a family in the RV doing normal stuff. Just the 2nd time in 3 years and there wasn't a good explanation for the other time either. I guess my plan is to just replace with a self resetting breaker.
-Chris

I would not use a self resetting breaker. Instead, I would use a breaker as large or slightly larger than the output of the converter.

You probably had a weak battery, converter went all out to charge it and exceeded the breaker capacity.

https://powerwerx.com/bussmann-cb285...reaker-surface

Charles

THenne1713 · 11-20-2022, 10:49 PM

That SMALL GRAY, w/ small button reset style, I believe is usually 30a or less, and higher ratings are usually the LEVER style? My 30a for slide also killed main Fuse panel and lighting; old age, internal corrosion can lead to HEAT trip on LESS than rated amps. GOOD LUCK, FIND LABEL FOR RATING AND ORDER/ CARRY A SPARE?

SJ-Chris · 11-21-2022, 12:27 AM

Quote:

Originally Posted by CharlesinGA

You probably had a weak battery, converter went all out to charge it and exceeded the breaker capacity.

Thanks for the idea. But my coach batteries are healthy and almost always at 100% because I've got more than enough solar. On top of that, the user was unplugging from a campsite which meant the batteries were also being charged all night. So it was not likely from a weak battery or converter charging the batteries.

-Chris

SJ-Chris · 11-21-2022, 12:55 AM

Quote:

Originally Posted by THenne1713

That SMALL GRAY, w/ small button reset style, I believe is usually 30a or less, and higher ratings are usually the LEVER style? My 30a for slide also killed main Fuse panel and lighting; old age, internal corrosion can lead to HEAT trip on LESS than rated amps. GOOD LUCK, FIND LABEL FOR RATING AND ORDER/ CARRY A SPARE?

The documentation I found online for my RV indicates pretty clearly that the reset breaker is 40a. Shows a diagram of the breaker and shows it in the location where it actually is in the RV. When I pull it, I will look to see if it says 40a on it.

I'll have to give it some more thought about whether or not I should replace the existing breaker with an auto-resettable breaker or not. My first thought was yes, but now I'm not sure. If, as it has been to date, the breaker trips for "no apparent reason" and then resetting it works fine and no other action is needed, then having an auto-resetting breaker would be nice. But if there was an actual (active) short then my understanding is that it will trip, reset, trip, reset, trip, reset and on and on and on until the breaker wears out. In a situation like that, I would prefer a manual breaker. Hmmmm.....

MichaelBarb · 11-23-2022, 10:44 PM

Most devices shutdown when voltage goes low. Still as voltage drops they all draw more current. I had a small fan once that plugged into the cigarette lighter. It would pop the fuse on the outlet when I shut off the engine and left the lights on. Battery was old. Went through a lot of fuses to figure this out and got rid of the fan. Replaced the battery before winter which I needed to do an. Never popped the fuse again.