Proper wiring for a battery disconnect switch

[AStravelers]

The REASON for disconnecting the negative cable first is so that when you are using the wrench and it accidently touches part of the frame or ground it is not a problem.

Accidently shorting the wrench to the frame when removing the positive cable first, not only can cause sparks, but can weld the tool to the frame so you can't get it loose. It can also quickly heat up the tool so if you grab it to pull it loose you can get a nasty burn. Also continuously shorting the battery to ground can possibly cause the battery to rupture or maybe explode.

About the disconnect on the positive or negative, I don't know for sure. I guess I could argue for both sides.

 

[Ex-Calif]

It will never be settled and everyone is correct.

Most switches you buy (I have installed a bunch) show the +ive being isolated. That's how I have always installed them but there are compelling arguments for the -ive.

Bottom line for me they both work equally. I am a "hard core" engineer. People toss around the "safety" word pretty fast and lose.

Either method for battery isolation is safe for any measurable quantity of safety.

 

[chuckbear]

Somehow I can't see a reason to have a disconnect switch in the disconnect position while the vehicle is going down the highway, which is when some posts indicate as an issue during a collision. The switch will mostly be used when in storage or at the very least in a resting situation. So collision issues should probably not be something that needs to be considered to determine the position of a cut-off switch. Trying not to muddy the waters. Chuck

 

[CharlesinGA]

The few trailers and motor homes I have had contact with had the disconnect in the positive side, apparently that is the way the manufacturers do it.

Is this in reference to a trailer? I have to assume that motor homes have disconnects already, and some trailers.

If a trailer, be sure and put the breakaway switch power feed directly to the battery so it cannot be disconnected accidentally.

Charles

 

[Gary RV_Wizard]

The hot wire is the one with significant potential on it with respect to ground. Many things are tied to ground, so you can be easily connected to ground depending on what you're touching, like a radiator, water faucet, sink, computer chassis, and other things you might not realize are grounded.

That's why disconnecting the battery negative from the chassis ground is the safest method in a negative ground vehicle. Nothing in the body of chassis is "ground" any longer - the only remaining ground is the actual battery negative post.

 

[Jkoht]

On my boat, which is the only thing I have a factory kill switch on, the manufacturer put it on the positive side. The housing and even the switch itself is all red, which I know doesn't necessarily mean it has to be on the positive side, but visually it makes it easy to work on if you have to do anything or add a new positive wire.

 

[Ex-Calif]

We haven't talked about the type of switch. My RV came with a (shudder) exposed blade type switch. Anything dropping on that could have easily made a short to ground.

I still am happy with the 1-2-All-Off switch. You can do it with relays but I like the positivity of the mechanical switch. When I get to rewiring the DC mess on Marvin This will be mounted near the driver's station in the coach.