Battery disconnect switch

[BertZegers]

There have been a debate about if the battery disconnect switch should be in the plus or in the ground. On tractors and heavy equipment the SINGLE POLE shut off switch is mostly used, and is often put in the positive battery wire. In my opinion it is safer to put the switch in the ground wire.
The costs are the same and the work is the same.
I have an example of an electric diagram with the battery shut off switch in the plus wire, and a diagram from a tractor company with the battery shut of switch in the ground wire. It is not complicated, and we do not have to make it more complicated than need be.
Because some people have claimed that it makes no difference if the switch is in the plus or in the ground wire, I have tried to make the difference understandable in a drawing.

One note: if the battery ground wire shorts to ground before the switch, no dangerous current path is created. If a plus battery wire shorts to ground before the switch, it might start a bad fire.

Let me know what you think.

 

[SPYDERLK]

Fair enough. No worry about exposed terminals on the switch is good for me.

 

[jaxs]

Fair enough. No worry about exposed terminals on the switch is good for me.

If a switch is needed,I agree with the logic about exposed terminals. Why would a switch be installed? It add's at least 4 connections to the original 2 that develop resistance and cause poor/no start situations.

 

[Wagtail]

If a switch is needed,I agree with the logic about exposed terminals. Why would a switch be installed? It add's at least 4 connections to the original 2 that develop resistance and cause poor/no start situations.

My first guess would be an anti-theft switch/device.

 

[Diggin It]

There's also an issue of battery drain if left connected full time. Some prefer to disconnect if the machine won't be used for long periods. I get concerned about some of the electronics that have any sort of programming that might be lost if left unpowered over time.

On topic of positive or negative, when I disconnect a battery in any vehicle for any reason, I pull the negative terminal/cable first. My reasoning is my clumsiness with tools and the possibility of shorting the wrench or driver to ground if I pull the positive first. In a passenger vehicle, I've heard of cases where that can cause the airbag to trigger.

I'd be less concerned about that with a fixed/mounted switch.

 

[LouNY]

Most battery disconnect switch instructions call for them to be installed in the ground cable.
Many are not rated to be installed on the battery hot lead.

 

[JerryK]

Does not matter if you install it on the ground or positive cable. Negative cable would be my choice. Most positive cables are factory configured with extra leads/possible fuseable links/etc... and usually the ground cable is just the one cable going to the frame. I put one on my Cat excavator on the ground, whilst the ground also had an OEM contactor in that lead to shut power off to the starter. There is absolutely no difference in the amps carried between the ground and positive cables. With DC current, operating the disconnect switch with little or no load is no problem. Operating the switch near rated load will quickly destroy the contacts. DC is nasty stuff. Working with batteries, it is always better to connect the negative last, disconnect it first unless you want to take the chance of shorting the positive to ground with your wrench.

 

[ptsg]

Installing the switch on the positive does have the disadvantage of exposing the terminals, on the other hand, it's easier if you want to run a separate wire for a radio, GPS trackers or something along those lines.

That being said, I still installed mine on the Positive side. It worked better that way for me.

 

[seville009]

My skidsteer came with a quick disconnect on the negative post installed by my dealer. He advised to keep it disconnected when not running because it would otherwise drain when off. He was right.

About five years later I out a new alternator in and that eliminated the drain; still have the disconnect on the battery, but I leave it connected and have never had the battery drain issue anymore.

The point made above about many other things being connected to the positive post is a good point.

 

[kthompson]

My volvo excavator has factory disconnect and right sure it is on the ground. It is a little extra anti theft benefit and to me helps limit drain and I prefer power disconnected if given reasonable option.