1993 travel trailer 12 volt exterior circuit breaker help

[CousinEddie]

I've got a 1993 travel trailer and I'm trying to understand the reasoning for using 2 circuit breakers in series. The first breaker is mounted to the frame at the front and is fed directly from the battery, I'm assuming it's 30 amp. When I took this breaker apart, the metal contact inside it is stamped with "30" on it. This breaker was damaged and getting replaced. The second breaker is inside of the junction box for the 7-pin harness connections and is fed from the first breaker, this one is labeled 40 amp. EVERYTHING in the 12 volt system is fed from the 40 amp breaker. That's what's confusing to me, I can't see the 40 amp breaker ever getting tripped. It's as though it's acting as a junction block and not a circuit breaker. If that's the case, I'd rather just remove it. Any thoughts would be appreciated. I can post pics if that would be helpful.

[franktafl]

Originally Posted by CousinEddie

I've got a 1993 travel trailer and I'm trying to understand the reasoning for using 2 circuit breakers in series. The first breaker is mounted to the frame at the front and is fed directly from the battery, I'm assuming it's 30 amp. When I took this breaker apart, the metal contact inside it is stamped with "30" on it. This breaker was damaged and getting replaced. The second breaker is inside of the junction box for the 7-pin harness connections and is fed from the first breaker, this one is labeled 40 amp. EVERYTHING in the 12 volt system is fed from the 40 amp breaker. That's what's confusing to me, I can't see the 40 amp breaker ever getting tripped. It's as though it's acting as a junction block and not a circuit breaker. If that's the case, I'd rather just remove it. Any thoughts would be appreciated. I can post pics if that would be helpful.

It protects the main feed (in and out) from the battery should anything short it (like a tire blowout or something else). I would definitely keep it, besides, what caused it to mess up in the first place? Besides, DC voltage is different than AC voltage in the respect that it uses more amps to operate devices. You may have an inverter in your rv to deliver 12 volts that is capable of 40 amps. The 12 volt system inside the rv is a branch circuit off of the 120 volt shore power. When you dry camp, you run off the battery and the inverter does not come into play (I don't believe).

[franktafl]

Originally Posted by franktafl

It protects the main feed (in and out) from the battery should anything short it (like a tire blowout or something else). I would definitely keep it, besides, what caused it to mess up in the first place? Besides, DC voltage is different than AC voltage in the respect that it uses more amps to operate devices. You may have an inverter in your rv to deliver 12 volts that is capable of 40 amps. The 12 volt system inside the rv is a branch circuit off of the 120 volt shore power. When you dry camp, you run off the battery and the inverter does not come into play (I don't believe).

sorry, should be converter not inverter... inverter is 12 to 120 converter is 120 to 12.


my bad. In my business, we call them power supplies and just want to know what voltage in and what voltage out.

[sundancer 87]

It seems like to me the 40 amp breaker would be first, just as a main breaker in a residential application. The 40 acting as the main and the the branch circuits protected by the smaller breaker, the 30 amp and so on.
There is a difference between DC breakers and AC breakers. Using an AC breaker in a DC application isn't recommended.

[wahoonc]

I wonder if one of them was set up to protect against reverse polarity? Or possibly one went bad and they previous owner just wired another one into the circuit?

Aaron

[CousinEddie]

Thank you for the reply. I understand the reason for circuit breakers, but what doesn't make sense is having 2 of them in series with different amperage ratings. The lower amperage breaker is always going to be the one to trip. That's what happened to mine. I got home from a 3 hour drive, and the 30 amp breaker was continually tripping and re-setting. The cause was the main large red 12 volt wire running into the camper was pinched between a floor joist and the frame of the camper. I had to slice open the underbelly plastic and go hunting. I'm assuming it's been that way since day 1 and just now chafed through the insulation to cause the short. Mine does have a converter with a built-in battery charger, but that shouldn't matter for my question.

[CousinEddie]

Originally Posted by sundancer 87

It seems like to me the 40 amp breaker would be first, just as a main breaker in a residential application. The 40 acting as the main and the the branch circuits protected by the smaller breaker, the 30 amp and so on.
There is a difference between DC breakers and AC breakers. Using an AC breaker in a DC application isn't recommended.

I see your point and that would make more sense. But I still don't see the 40 ever tripping. If the 30 is the one tripping, it just seems strange to me to even have a 40 in the circuit.

[CousinEddie]

Originally Posted by wahoonc

I wonder if one of them was set up to protect against reverse polarity? Or possibly one went bad and they previous owner just wired another one into the circuit?

Aaron

I was wondering about the possibility of someone prior adding a second breaker. Based on the connections and mounting, it looks like other stuff on the camper, which is why I'm guessing it's original :confused. That's why I was hoping someone out there with a similar vintage might chime in. Thanks for the reply though.

[sundancer 87]

Originally Posted by CousinEddie

I see your point and that would make more sense. But I still don't see the 40 ever tripping. If the 30 is the one tripping, it just seems strange to me to even have a 40 in the circuit.

Here's my take on why there are two of them. The 40 amp will disconnect the battery from everything. In the event you wanted to remove/replace the 30 amp breaker you would only have to throw the 40 amp one, instead of physically removing battery cables for safety purposes.


You could delete the 40 amp breaker and go with the 30 amp one. Or you could get serious and break out all the circuits on the 30 amp one and fuse each branch.


Why they do what they do or what a previous owner does is not easy to answer. You have options to make it your way.

[CousinEddie]

Thank you all for the replies! I'm going to put it back together with the 40 amp breaker in place, mainly because it isn't hurting anything. I was just looking for opinions as to why it's there.

[persistent]

Originally Posted by CousinEddie

… 2 circuit breakers in series. … mounted to the frame at the front and is fed directly from the battery, I'm assuming it's 30 amp.

Wire Size Determines Maximum Breaker Size
My Kodiak Cub has a 40 amp breaker there. It is a self resetting breaker like yours,. It protects the battery wire and provides power to the emergency electric brake should your TT become separated while moving.
1) What size is the wire to the battery from this breaker. Wire size is the key to breaker or fuse size. Load capacity and charging capacity are important, but wire size determines the maximum breaker size.
My Cub has a 6 AWG wire with a 40 Amp self resetting circuit breaker. It connects the emergency electric brake and 7 pin tow vehicle connecter. It originally also connected to the TT 12 volt converter. I installed a separate 50 amp manual breaker. It connects the battery to the TT 12 volt service. It delivers 50 amps through about 20 feet to the TT 12 volt converter unit when my 120 volt inverter is running and it is used to disconnect the battery when shore power is connected for long periods.

12 volt wire tables:
6 AWG is good for 50 amps up to 28 feet.
8 AWG is good for 50 amps up to 16 feet
8 AWG is good for 40 amps up to 28 feet
10 AWG is good for 40 amps up to 16 feet
10 AWG is good for 30 amps up to 24 feet
12 AWG is good for 30 amps up to 16 feet
The max distances are for both load and charging purposes. Using larger wire is sometimes used to reduce line loss and raise voltage at the far end.
Warning! Do not use these values for AC wiring such as 120 volt. Larger wire sizes are needed for AC circuits.

"inside of the junction box for the 7-pin harness connections labeled 40 amp. EVERYTHING in the 12 volt system is fed from the 40 amp breaker."
I assume the 7-pin harness is the connector to the tow vehicle.
1) Is the 40 amp breaker a self resetting, or manually controlled? If it is manually controlled, it can be used as a battery disconnect switch. It may have been installed to prevent "boiling" the battery during long periods of charging from shore power. In this case it is not the 40 amps that is important. It is the manual switching capability.
2) Are you sure the electric brake emergency activation switch is not connected near the 30 amp breaker?
Assuming nothing is on the 30 amp breaker side as you stated and the 40 amp breaker is manually reset, you should move the electric emergency brake switch wire to the 30 amp side so it will activate even if the 40 amp breaker is off.

" I can post pics if that would be helpful"
Posting pics would help greatly.

Paul Bristol

[persistent]

The tow vehicle 12 volt pin should also be connected on the 30 amp breaker side of the 40 amp breaker. The tow 12 volts charges the battery when the 40 amp breaker is off which is necessary for the emergency electric brake.

[CousinEddie]

The 40 amp breaker is self resetting. The emergency brake activation switch was connected to the 40 amp breaker. Pictures wouldn't do much good at this point. I already removed both breakers and took the junction box apart to re-do the wiring. I'm installing a larger box that is weatherproof and moving the 30 amp breaker inside of the box, so they'll both be in there. Also putting in new wires from the battery to the junction box.