Keep tripping main breaker Randomly, sometimes after a week!

[aaron7]

I feel a long confusing post coming... please read the whole thing before replying!


1979 Shasta Class-C

We're full timers and not having power is very, very bad!!

Since we've bought it we've had problems with the main breaker tripping randomly.


Doesn't matter if you have anything on or even plugged in; seems to just be at total random.  Sometimes it'll go a week without issue, sometimes it'll do it once a day, and sometimes it'll pop every hour!

We've replaced the breaker (P20) with a new one hoping it was just weak. Wasn't easy to find! No change.

There is only one other breaker and that's strictly for the air conditioning unit.

I've removed all the 12v fuses from the converter to isolate the system and it still happens.

I've disconnected the fridge at the back; both 12v and AC.

Nothing is plugged into any outlet.

We do not use the water in the camper so the water heater is not used.

We don't have LP (leaky tank) so the furnace is not used. Did work fine before the LP was depleted.

Everything else functions fine. Fans, lights, all outlets, etc.

Disconnected the house battery in case it was shorted (though it's 6 months old); no change.

Also does not seem to be temperature related. Happened in the summer, happened the other night when  it was 30 out. Morning, noon, night... doesn't change.

At this point everything points to either the DC converter itself or a bad connection somewhere in the AC lines that's causing resistance and building up heat till that breaker pops.

Once the breaker has tripped it cannot be reset till you wait around 10 minutes. If you try and reset it before then it trips immediately. Also points to something getting hot.

I do see the main line feed to the plate the breakers mount to is melted at the end though that could be old.

I put a good fan on the converter insides hoping that was the problem... also not the case.

Problem is... I have no idea where to start.

Aside from gutting the damn thing, how the heck do I troubleshoot this further???

[aaron7]

Yes I understand it's very dusty! That's only recent due to the fan I put on top of it thinking it was a heat issue. I'll be sure to vacuum it all out!

The water heater is about 6 years old but I do believe it's LP only. If it also has electrical power I don't believe it's connected.

I do believe you are correct in thinking it's in one of the AC lines though. But since there's only one breaker for EVERYTHING AC I'm not sure how to go about tracing lines!

[legomybago]

I think I would pull each out going circuit one by one, and see when it stops tripping the breaker?

[sasktrini]

That coil of white (neutral?) wire could be generating excessive heat or resistance.

Your DC circuits run fine off the battery?

I would definitely dust the box out, and ensure there is clean unobstructed airflow.  Don't store any items where it could block air to the unit.

You could pull your AC outlets from the walls and inspect to see if any of them are shorting out.

[aaron7]

legomybago, the fuses are for the DC side of the circuit.

As stated in my first post, I've already removed the fuses and determined it is not a short on the 12v side.


sasktrini, all DC circuits work fine off both shore power (converter that is) and the house battery.

Box wasn't dusty before all this happened (that's due to my additional fan) but I'll clean it out just the same.


I guess all there is now is to do just that; remove every outlet and inspect.

Just getting cold in here!!

Sigh.

[sasktrini]

If that coil of wire seems excessive, it could be trimmed.  Long coiled wires generate more heat than short straight wires.  Like the coils of a transformer.  Could be impeding internal air flow.  Except it's probably original, so may be barking up the wrong tree.

If ambient temperature (hot days) are a clue, you may simply have to tighten down on all the AC connections, as they expand and contract with temperature changes.

[bakerman]

Start by looking at each of your electrical contact points both positive and grounds. You apparently have a interim bad connection that causes your breaker to over heat and it flips. It could possible be your plug at the electrical source ,if you have a ohm meter check your voltage then check the continuity. Remember when checking all points have the coach unplugged loosen all connections looks for hot spots and reterminate as required. Hope this helps just something loose can cause heat build up.   

[DaveVA78Chieftain]

That is a old Magnetek Power Center.  Wiring diagram for the converter section is on pdf page 19 of http://www.hayseed.net/~jpk5lad/RV%20Information/MagnaTek%20Pwr%20Converter/RV%20Binder1.pdf

Connection of the converter to the 12 volt side is shown on pdf page 18 under the Linear Type section.

Does the original fan (M; FM1) still work in the converter (back right hand side)?  If not, then I would suspect that when the temperature in the converter unit heats up and temp switch TS2 switch turns ON to turn fan ON, the fan is drawing to much current causing the main breaker to open.

The other temp switch TS1, is used to shut down the converter if the inside temp gets to hot.

Dave

[eXodus]

Disconnect every power source (shore,gen) - make sure every outlet is free

- Disconnect the converter
- then measure the resistance between hot and, ground, neutral. Should be indefinite or at least very high.

By this method you can be sure that it's not in the wiring, which would be the time consuming to find. But very important because a half-short in the wiring could produce so much heat that something could start burning.

Normally how breakers are constructed, if they are not able to reset after tripped, it had been overloaded for a longer time which causes heat to built up. If you just got a short spike the breaker are normally easy to reset.

Try and Error method: You could just install a additional breaker for the converter. A 10A should be enough, don't get the same size as you main - always smaller. If now this breaker gets tripped you also know whats going on.
And if not, you've got separate breaker to turn of the converter.

[aaron7]

Well everyone, it took a LOT of testing and redoing but we got it!

In the 5th pic down you can see the main power feed to the hot plate the breakers mount to was melted. This was the big clue that I didn't pick up on.  You can see the lug it screws into is cocked and not at a 90^ angle in relation to the hot plate.  Because this part is notched on the side (to butt up against the hot plate) being cocked meant that only the SCREW was transferring power between the wire and plate!  I took it all apart, put it back together properly, and tried it... but the breaker still popped.

Not to be discouraged I swapped the AC and Main breaker wires (to use the AC breaker for the mains) and guess what... it's been fine since!!!

So I think the excessive heat from the bad mains connection made the P120GF breaker pop too frequently and ruined it.

Only issue now? That breaker is $130 new! And no chance I'm getting a used one!

That can wait though... we don't need the AC till next year

So thank you everyone for all the suggestions and help!!!

[pvoth1111]

get an amp meter and measure the current.....my meter has a feature that measures it over time....also breakers get old and become weak...you could get a new breaker....and the breaker tripping often will weaken it as well.....get a amp meter turn things on and off and measure the amps...you will find it....its not magic just electricity.