Which side of batteries for cut off switches?

RonD2 · Post by **RonD2** » Fri Dec 11, 2020 9:59 am

Hi Wes,
Perhaps I should start another thread to bring this up.

Maybe I'm missing something, but above you say that a battery master disconnect switch should be installed to interrupt the ground (negative) side of a battery, yet also show the relay schematic that interrupts the positive side of the battery. For safety, I believe that a battery master disconnect switch should only be installed to interrupt the positive (hot) side of a battery and that's how I installed mine.

Interrupting the ground enables a large safety hazard because it leaves the entire hot side of the circuit completely intact and waiting for a human to inadvertently contact something hot and complete the circuit to ground with a body part or a tool. Not good. Ground connections should always be intact when working around electricity.

Let me know if I should move this to a new thread topic and I will.

Post by **wesk** » Fri Dec 11, 2020 12:44 pm

Ron,

I would avoid opening another can of worms in the middle of another guys post. Probably better when you feel urges like these to PM the guy with your thoughts before changing the direction of the other guy's post. Try googling the current flow directions in DC circuits.

RonD2 · Post by **RonD2** » Fri Dec 11, 2020 1:17 pm

Sure thing Wes.

My apologies to Rick and everyone for being the guy to stray off topic. I should know better by now.

RonD2 · Post by **RonD2** » Fri Dec 11, 2020 2:23 pm

Thanks for moving this thread to new topic Wes.

Try googling the current flow directions in DC circuits.

There's nothing like a refresher reading of basic DC circuit theory to uncover brain cells buried long ago. Are we talking current flow (positive to negative), or electron flow (negative to positive)?

A main battery master disconnect switch should be installed off the battery positive (+) terminal post, to interrupt all load current flow.

Ideally, the switch belongs as near as physically practical to the (+) battery post, should be directly connected with nothing else in between, and using the shortest possible wire of the correct gauge. Some folks may choose longer wire runs to and from the switch in order to hide it as part of a "defense-in-depth" theft deterrent. Naturally, the switch has to be properly rated to handle the load current and voltage, because everything is running through it when it's "on".

Installing a switch off the battery negative (-) terminal to interrupt ground is tempting fate and asking for trouble, for the previously mentioned reason.

Here's mine, a mil-spec switch: