Batteries and wire gauge questions

[MarkEHansen]

Originally Posted by apachewolf

I always use a master disconnect on the NEGATIVE side, that way all power is disconnected, no guessing about "phantom" loads draining the battery when you think it is disconnected. In car service you always disconnect the negative first to ensure total disconnect.

Happy camping.

That is not why you disconnect the negative cable first. You disconnect the negative cable first because disconnecting the positive cable first runs the risk of shorting your wrench to ground.

As for a battery disconnect, disconnecting either the negative or positive makes absolutely no difference. Once the circuit is interrupted, no current will flow.

The reason why there are phantom loads in RVs even when the battery disconnect is off is due to those loads being attached to the battery before the disconnect - as they need power all the time (and should not be "disconnected").

[LHaven]

In my old rig, if you disconnected the positive clamp, you also had to remember to disconnect the obscured wires connected to the positive screw port. Disconnecting the negative side instead was one and done.

[Frank G]

Caution... careful with the placement of a battery disconnect. The following conversation is about the brake away switch and how it gets it's power. One of the wire bundles you have pictured comes form the Tow Vehicle power cord. There is a neutral wire (-12vdc) grounded to the frame, the TT (-12vdc) battery is also grounded to the frame. Both are not to be interrupted. A hot wire (+12vdc) from the TV that goes straight to the TT Battery. Off of this Circuit is the +12vdc power to the Brake Away Switch. In a separation of the two (TT and TV), the system is relying on power from the TT Battery to set the TT brakes. The brake away switch power connection to the TT must be before any circuit breakers or disconnects.

On our 2017 Laredo 5th wheel there are (2) two leads connecting to the positive terminal of the battery. The heavy lead goes to the disconnect the other to the brake away switch.