Thermal Breaker

Here is basic information on circuit breakers.


"Thermal magnetic circuit breakers, which are the type found in most distribution boards, incorporate both techniques with the electromagnet responding instantaneously to large surges in current (short circuits) and the bimetallic strip responding to less extreme but longer-term over-current conditions. The thermal portion of the circuit breaker provides an "inverse time" response feature, which trips the circuit breaker sooner for larger overcurrents but allows smaller overloads to persist for a longer time. On very large over-currents during a short-circuit, the magnetic element trips the circuit breaker with no intentional additional delay"

It is possible that the circuit breaker may not want to reset as age a numerous trips can weaken the internal springs. Thus needs to be replaced.

dougrainer wrote:
There is NO 120 volt Thermal Breaker that will auto reset in any motorhome. Especially a 25 year old 30 amp RV. I will bet the CG system was OFF and when it came back on she got her 120 power back. Odds are also on a 1991 WINNE/Itsasca 30 amp RV there is NO 30 amp transfer switch. Back then, Winne used a hardwire plug in the shore Cord compartment and you had to plug in the 30 amp cord to that receptacle to get Genset power. Doug

I agree with the lack of a thermal, and the probability that there is no transfer switch. The CG power is not the issue however. The OP is the owner and builder of the CG, and a all around talented guy. He would be the first to know if the power was out.

There is NO 120 volt Thermal Breaker that will auto reset in any motorhome. Especially a 25 year old 30 amp RV. I will bet the CG system was OFF and when it came back on she got her 120 power back. Odds are also on a 1991 WINNE/Itsasca 30 amp RV there is NO 30 amp transfer switch. Back then, Winne used a hardwire plug in the shore Cord compartment and you had to plug in the 30 amp cord to that receptacle to get Genset power. Doug

A six-hour 120V thermal reset is BS plus no such thing in a 25 year old motorhome or any MH. For $12 I would replace the 30 amp breaker for her if I could not find any loose connections.

The last two replies mention inverters. I would guess that a 25 year old, thirty amp RV has a simple converter, which would have nothing to do with this issue. There is a possibility that the main breaker is failing, and intermittently failing to provide power. If the issues reoccurs, I would check both sides of the breaker with a meter, to confirm that power is actually flowing through the breaker. Remember that this breaker is typically wired backwards, as compared to a typical residential panel. The incoming power wire from the shore cord is attached to the screw lug on the breaker. Power flows through the breaker and feeds the bus bar, which all the branch circuits are attached to. As for a thermal reset, doubtful. As an electrician for 25 years, I have never seen one used in an application like this. A quick search online offers nothing about 120V auto reset thermal breakers used in RVs, except as a component inside of an inverter. If this was an odd situation, where there really is a thermal overload breaker in the 120V system, I would also expect to see a reset button. That said, I've never encountered a non-resettable, thermal only breaker in any 120V system. Not to say that it's never been done, but it sure isn't typical. In this case, I would be real concerned about the integrity of all the 120V connections from the cord cap to the panel box. This could easily be a heat related issue, due to a high resistance connection. I would trace the wiring, and pay particular attention to any connections and splices. The shore cord typically ends in a 4" square junction box, where it converts to 10/2 Romex. I would definitely want to tear into that box and look at condition of the spices. If the 30 amp plug on the cord is a replacement, I would take it apart and check all connections. I would also retighten all the terminal screws in the panel box.

The other issue could be a failing transfer switch, if it has one. On a lot of the older/cheaper units, the transfer switch was an option, and you simply plug the cord into a 30 amp receptacle fed by the generator.

Max, I hope you encourage this customer to have a qualified electrician take a look at the 120V part of her electrical system. I have done a lot of troubleshooting, and repair work, on 120V systems. Problems that "cure" themselves tend to make me nervous.

Our 2000 watt Xantrex inverter/charger has two breakers behind the main battery cable and very hard to see. The lower one is usually tripped if we lose power to the passenger side of the coach, even if using the inverter/charger for battery charging only.

Don't know if this may have been an issue ot not but I know I searched one time for the reason I lost power to outlets. I have a 50 amp coach and I was plugged into a 50 amp pedestal but most inverters(if she has one) only have a 30 amp pass through circuit. Somehow I over loaded this pass through and a number of the outlets went out. Finally, I reset the inverter(some inverters may have a thermal auto reset) which fixed the whole situation. Just a thought...

Most breakers are thermal and current.
What is V/A?
main breaker is tripped reset it.
Your tech is wrong for it being auto-resetting!

enblethen wrote:
120 volt power is fed through the circuit breakers like in a house.
Most circuit breakers in order to reset must be turned off applying light pressure toward off. Then main breaker would be turned on followed by branch breakers one at a time.
Auto resetting breakers are used commonly on 12 volt DC system and located adjacent to the batteries or in the battery control center.

It was the Ladys 120v power. 12 v dc was fine. That is the stumper, 120v ac fine at input to and through gen. sw.load tested, but not at 30ac dist. panel. Where and what interrupted the V/A ?
I be never heard of a thermal breaker in the line between . Why would there be one?

120 volt power is fed through the circuit breakers like in a house.
Most circuit breakers in order to reset must be turned off applying light pressure toward off. Then main breaker would be turned on followed by branch breakers one at a time.
Auto resetting breakers are used commonly on 12 volt DC system and located adjacent to the batteries or in the battery control center.