Positive or Negative to Battery switch

Someone please explain how this works because I'm missing it completely.

Other than the wiring economics of switching negative to the frame, as in door switches, I fail to see how it saves life or arching.

RJsfishin wrote:
Quote:
As someone else said in the automotive world they switch the ground, but in this case you need to properly disconenct the positive to be safe.
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Where did that BS come from ?
!

That was one of the things I learned in the electronics classes at the manufacturers regional training center when I was a tech. The claim was that by disconnecting the negative side of the load there was less arcing hence the components would last longer. I don't know whether that actually pans out in real life, but it is what I was told is the way they design their cars. When I think about it now though, I bet they were referring to the switching that goes on inside circuit boards and not the large loads like the starter or headlight switch.

joshuajim wrote:

RJsfishin wrote:
Quote:
As someone else said in the automotive world they switch the ground, but in this case you need to properly disconenct the positive to be safe.
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Where did that BS come from ?
In reality, every switch and circuit breaker in an automobile, and RV, and boat, is in the positive wire.

Really? Try running 10 or 20 amps through a circuit board and watch the factory smoke leak out,

What does that even mean?
If a board is rated to pass 20A, then that's what it does.

RJsfishin wrote:
Quote:
As someone else said in the automotive world they switch the ground, but in this case you need to properly disconenct the positive to be safe.
----------------------------------------------------------------------
Where did that BS come from ?
In reality, every switch and circuit breaker in an automobile, and RV, and boat, is in the positive wire.

Really? Try running 10 or 20 amps through a circuit board and watch the factory smoke leak out,

Quote:
As someone else said in the automotive world they switch the ground, but in this case you need to properly disconenct the positive to be safe.
----------------------------------------------------------------------
Where did that BS come from ?
In reality, every switch and circuit breaker in an automobile, and RV, and boat, is in the positive wire.

Take it to house electrical,.........which wire is every circuit breaker and light switch put in ????? You only get 4 guesses !

Beemerphile1 and Wgriswold have it correct.

You have a trailer (5th wheel) and that has an emergency breakaway switch wired into the circuit. If the trailer becomes disconnected from the truck the brakes will engage and hopefully stop the trailer before it kills somebody.

Considering the breakaway needs 12v to engage you have to interrupt the positive side of the power BUT wire the breakaway around the cutoff and directly to the battery. This ensures that the emergency brakes will work regardless of whether you remember to engage the cutoff switch before towing. There is no parasitic load from the breakaway switch, it's just an on/off switch.

If you interrupt the ground your emergency switch power will not get back to the negative terminal of the battery unless you run a separate ground wire. But this will also allow the rest of the coach to use that same ground wire effectively negating the cutoff in the first place.

As someone else said in the automotive world they switch the ground, but in this case you need to properly disconenct the positive to be safe.

Electrically, it doesn't matter which terminal on the battery that you connect the disconnect to. I am assuming that you will disconnect at the battery terminal. Either one will disconnect everything on the trailer.

However, there is a good reason to use the positive. If the disconnect is at the positive you can wire the breakaway switch positive ahead of the disconnect switch and then even if the disconnect is open the trailer brakes will still engage if it comes loose from the TV.

If the negative is disconnected the only short possible would be a direct accidental connection (a wrench or screwdriver)between the two terminals of the battery. If the positive is disconnected the possibility of a direct connection of the terminals still is a hazard and in addition any connection between the positive terminal the the frame of the trailer will result in a short. Earth ground has nothing to do with our trailer's 12V system.

D.E.Bishop wrote:
It looks like this has pretty well played it's self out, however, I have a question. I have looked for a description of a Torx box without luck. Being that the discussion is about a TH and I'm more familiar with MoHo's, I kindda figure it has to do with towed RV's rather than powered RV's. Anyway, searches provided nothing but ads for TOXR wrenches.

Try TorkLift Power ArmorTorklift

ashnic wrote:
Just got my Torx box installed and my battery switch. Wanting to wire it up tomorrow. I believe I know (negative) but thought I would ask do I put the switch on the Neg or pos? Thanks for your help guys..

From a safety prospective, and engineering, and RIVA, and NEC you always switch the positive. After all that is where the fuse or breaker goes.

joshuajim wrote:
Not that it is relevant, but almost all computer controlled circuits like in cars are switched on the negative, Far less power handling requirement.

Whats that mean? Watts is watts, regardless of how its switched.

For electronics it much more straight forward to ground a junction than pass current.