Battery disconnect wiring

I placed a disconnect close to the positive side of the battery and use it when I want everything completely shut off on my trailer. When I'm doing an equalization of my batteries I just turn off the factory installed disconnect.
So really it depends on how you want to manage your power.

Positive is the norm and is particularly important if it is a trailer.

Lynnmor wrote:
It really doesn't matter.

Contrary to popular opinion, I do wire the breakaway switch so that it turns off as well. If the switch gets accidentally pulled, or a short in the brake wiring occurs, I can simply turn off the power hopefully before there is a fire. There is no fuse in the brake circuit.

This is dangerous because if you forget to turn the battery back on, you have no breakaway brakes.

While I agree with disconnecting the negative wire first, that doesn't apply in this case. The disconnect switch should be on the positive side of the battery since you are not risking shorting a wrench handle to ground while removing it. That way, if it is a trailer, you don't disconnect the breakaway brakes (which SHOULD be connected directly to the battery). If it is a MH rather than a trailer, it really doesn't matter.

skipro3 wrote:
It is common practice that when you disconnect a battery for any reason, you disconnect the negative lead first, then the positive. Your situation shouldn't be any different. Disconnect the negative first, even if you are not going to disconnect the positive.
The reason negative is disconnected is because the electricity flows from negative to positive.

The main reason the negative is disconnected first on a vehicle is that a short from the tool being used to remove the terminal to ground would not cause problems for the negative terminal, but could be quite dangerous with the positive terminal: wrenches getting welded in place, batteries exploding, those sorts of difficulties. Once the negative is disconnected, shorting accidentally from positive to ground does not cause fireworks. For an (enclosed) disconnect switch, this is not a concern as one isn't mucking about with metal tools on the connectors to turn things on or off.

On an old vehicle with a positive ground system, the positive pole would be disconnected first.

What direction electricity flows in depends on what the charge carriers are. In metals, they're practically all electrons and so flow from negative to positive. In some areas of semiconductors or in some conductive solutions (i.e. some electrolytes), the majority of charge carriers are positive and so they flow from positive to negative. In some cases there may be both positive and negative charge carriers.

It really doesn't matter.

Contrary to popular opinion, I do wire the breakaway switch so that it turns off as well. If the switch gets accidentally pulled, or a short in the brake wiring occurs, I can simply turn off the power hopefully before there is a fire. There is no fuse in the brake circuit.

skipro3 wrote:
It is common practice that when you disconnect a battery for any reason, you disconnect the negative lead first, then the positive. Your situation shouldn't be any different. Disconnect the negative first, even if you are not going to disconnect the positive.
The reason negative is disconnected is because the electricity flows from negative to positive.

X2

It is common practice that when you disconnect a battery for any reason, you disconnect the negative lead first, then the positive. Your situation shouldn't be any different. Disconnect the negative first, even if you are not going to disconnect the positive.
The reason negative is disconnected is because the electricity flows from negative to positive.

It doesn't matter.

Ron3rd wrote:

dons2346 wrote:
Break the positive as close to the battery as you can. This keeps the positive from grounding out further down the line and causing a short to ground.

That's my opinion too.

On the other hand, if the negative connecting to the chassis ground is broken, then shorting the positive line to ground doesn't cause any difficulties either (well, assuming there are no voltage sources on the "other side" of the system like the converter, which applies in either case). No current flows because the negative lead is disconnected and you have no circuit.

Admittedly, I guess I do prefer switching the positive side, but not for any really solid reason other than it, well, feels like the proper way to do things. It's like washing dishes in the left side of the sink and rinsing them in the right side, which just seems to me like the proper direction to do things in, for no really scientifically justifiable reason.

dons2346 wrote:
Break the positive as close to the battery as you can. This keeps the positive from grounding out further down the line and causing a short to ground.

That's my opinion too.