Charge wire not fused at the coach

[dryfly]

We keep missing the point that the RV side of the 12v+ (charge wire) in the 7-way plug is connected to the RV battery/12v bus and is hot even when the truck is disconnected. That wire will satisfy the 15 minute rule. You don't need a separate circuit to satisfy the emergency braking rule although some RVs may have one.

Maybe we are saying the same thing but the OP was about putting a fuse in the 12vdc charging circuit from the tow vehicle. Unless I'm misunderstanding, the break-away circuit has nothing at all to do with the charging circuit from the truck. The break-away switch is a normally open circuit, and receives power from the trailer battery. Please correct me if I'm wrong, but it's still gonna function if the truck is nowhere in sight.

[LMagelitz]

Maybe we are saying the same thing but the OP was about putting a fuse in the 12vdc charging circuit from the tow vehicle. Unless I'm misunderstanding, the break-away circuit has nothing at all to do with the charging circuit from the truck. The break-away switch is a normally open circuit, and receives power from the trailer battery. Please correct me if I'm wrong, but it's still gonna function if the truck is nowhere in sight.

Unfortunately, the breakaway circuit and the +12v charging wire are not separate and distinct circuits on some trailers, mine included. My 310 has a junction box right behind the pin box where Grand Design tapped into the +12v charging wire to supply power to the breakaway switch. When it’s pulled, the brakes apply. So there are actually a couple of issues here.

1. On my 310 there is no overcurrent device on the coach side to prevent the RV batteries from feeding a fault anywhere along that +12v charging wire. That’s a problem if the wire gets chafed or pinched somewhere and shorts out. The truck side isn’t a problem, as there is a fuse that will prevent the truck batteries from feeding any fault along that +12v charge wire. I can fix the RV side of this by installing a circuit breaker in the front compartment of the RV where the charge wire connects to the RV 12v system/coach batts.

2. @Jomani brought up an excellent point earlier, which is the second issue. If you have the RV actually break away from the tow vehicle, the 7 pin connector will be ripped out, or the cable will be torn away from the trailer. If this causes a fault in that +12v charging wire, and that wire is the one that supplies voltage to your breakaway switch, the brakes may not apply. This is an argument for having separate and distinct circuits for charging and breakaway, but that’s not what I currently have.

[MccNeo]

Unfortunately, the breakaway circuit and the +12v charging wire are not separate and distinct circuits on some trailers, mine included. My 310 has a junction box right behind the pin box where Grand Design tapped into the +12v charging wire to supply power to the breakaway switch. When it’s pulled, the brakes apply. So there are actually a couple of issues here.

1. On my 310 there is no overcurrent device on the coach side to prevent the RV batteries from feeding a fault anywhere along that +12v charging wire. That’s a problem if the wire gets chafed or pinched somewhere and shorts out. The truck side isn’t a problem, as there is a fuse that will prevent the truck batteries from feeding any fault along that +12v charge wire. I can fix the RV side of this by installing a circuit breaker in the front compartment of the RV where the charge wire connects to the RV 12v system/coach batts.

2. @Jomani brought up an excellent point earlier, which is the second issue. If you have the RV actually break away from the tow vehicle, the 7 pin connector will be ripped out, or the cable will be torn away from the trailer. If this causes a fault in that +12v charging wire, and that wire is the one that supplies voltage to your breakaway switch, the brakes may not apply. This is an argument for having separate and distinct circuits for charging and breakaway, but that’s not what I currently have.

Very good point. I will be looking at my wiring arrangement to see where the Break-Away power is tapped in. If it is in the 7-Way J-Box, I will be modifying wiring to correct that along with installing a appropriately sized breaker.

BTW, I have a tandem axle totally enclosed Haulmark cargo trailer configured for motorcycles that I know for a fact isn't protected now that I think about all this. That trailer will definitely need some re-wiring also.

[ajg617]

1. On my 310 there is no overcurrent device on the coach side to prevent the RV batteries from feeding a fault anywhere along that +12v charging wire. That’s a problem if the wire gets chafed or pinched somewhere and shorts out... I can fix the RV side of this by installing a circuit breaker in the front compartment of the RV where the charge wire connects to the RV 12v system/coach batts.

All of my wires coming into and out of the junction box are wrapped with an outer bundle of insulation.

Where are you seeing the charge wire connection in the front compartment? I know mine has to have it, but I sure can't find it. I wonder if there is any wiring difference with disc brakes?

EDIT: Looking further, I'm assuming it is under the cover circled in red in the pic below.

[440scout]

All of my wires coming into and out of the junction box are wrapped with an outer bundle of insulation.

Where are you seeing the charge wire connection in the front compartment? I know mine has to have it, but I sure can't find it. I wonder if there is any wiring difference with disc brakes?

EDIT: Looking further, I'm assuming it is under the cover circled in red in the pic below.

Following this thread.

[LMagelitz]

All of my wires coming into and out of the junction box are wrapped with an outer bundle of insulation.

Where are you seeing the charge wire connection in the front compartment? I know mine has to have it, but I sure can't find it. I wonder if there is any wiring difference with disc brakes?

EDIT: Looking further, I'm assuming it is under the cover circled in red in the pic below.

Yes, take off that little cover and you will probably find it. I have disc brakes too.