Battery cut off switch

I've always been told to put it on the Neg. side.

BTW, I had many problems using that kind of cutoff. I finally went toe the blade type cutoff.

I had one of these on a collector ('40 Buick) car and it worked fine for me for about five or six years. It was on the car when I bought it, so who knows how long it was in service.

As I said, I had no problems with the item. Perhaps that's because I was using it on a starting battery and not in a deep cycle constant draw environment.

I don't really recall if the connector was installed on the positive or negative post. I guess the advantage of using it on the negative post would be not dealing with the potential "spark" issue when used on the positive side.

I hope this helps.

Robert
Huntington Beach, California

I use one of the two battery switches and I put it on the positive side of the batteries. I can pick "Battery 1", Battery 2", "Both" or "Off".

Conventionally it is put in the positive side, but electrically it will work in either side. Put it where it fits best, is the most convenient to access, or the easiest to install.

If this is for a trailer it MUST be in the positive side. Wire the breakaway switch directly to the battery before the switch.

I use a 250a that is used on race cars. Put it in a weather box outside the compartment. No need to open the compartment to switch. $25 from Summit Racing.

beemerphile1 wrote:
If this is for a trailer it MUST be in the positive side. .

Would like some facts to why it "MUST" be on the positive side.

Like others said either side...but...

With this type of device the Neg. would be better. If you have the battery disconnected and then plug in the trailer the disconnected end will be powered by the converter. If that loose end contacts the frame you can create a short.

The break-a-way switch is only a problem if you don't connect the battery before moving the trailer.

If the switch is in the ground/negative, someday, someone, somewhere will tow the trailer with the switch open and the breakaway system will not be functional. That is a dangerous and illegal situation. There is no real benefit to switching the negative, so why take the risk of something that is almost inevitable to happen eventually.

Learjet wrote:
...If you have the battery disconnected and then plug in the trailer the disconnected end will be powered by the converter. If that loose end contacts the frame you can create a short....

Why would there be a loose end anywhere? The topic is about where to locate a disconnect switch.

100ton wrote:
I guess the advantage of using it on the negative post would be not dealing with the potential "spark" issue when used on the positive side.

Sparking has to do with the current flowing and voltage across the switch. That's the same regardless of whether the switch is on the pos or neg. I can't see that it matters which side you switch, although convention is to switch the pos.

beemerphile1 wrote:
If the switch is in the ground/negative, someday, someone, somewhere will tow the trailer with the switch open and the breakaway system will not be functional.

The breakaway needs to be wired directly to the battery to function. If it's wired after the switch - regardless of whether the switch is on the pos or neg, it won't work with the switch off. If the switch is on the neg, then the breakaway needs to go to the battery negative directly before the switch. The problem with that is where the negative is tied to the frame. If your breakaway uses the frame as its ground, then tying the breakaway negative to the battery negative before the switch will try to power anything else connected to the frame - regardless of whether the switch is on or off. I'd put the switch on the positive, but if your breakaway design used an isolated ground, it would be perfectly fine to run that ground before the switch and put the switch on the negative after that connection point.