Battery Disconnect Switch...Positive or Negative

I plan on installing a battery disconnect switch on our BC this spring when I bring it out of storage. My first inclination was to put the switch on the negative leg of the circuit. As I was considering this it came to mind that somewhere I had read and/or heard that the switch in this type of circuit should be on the positive side.

Does it make a difference?? Is it safer one way over the other?

Don't really want to do anything that would jeopardize the inverter or other electronics.

I have always been told and done.... Disconnect on the positive.

I always put the switch on the B+ side in my rigs and in all boats.

My battery disconnect is on the positive side and it came from the factory that way.

I installed ours on the positive side. I believe it's much safer this way. It would be easy for something to ground out to the frame, I suppose, and that would complete the circuit even if the negative terminal to the battery was off.

I always disconnect the ground because I have always had great success doing it that way.
The collector cars I store over the winter has the ground side of the battery disconnect over winter.
Its the only way the batteries will have full power the next spring when I start the vehicles.
The batteries hold their charge better with the ground disconnected. Don't know why but it works.

When you boost a car with jumpers or booster cables the ground is what is the most dangerous connection.
The batteries will blow up with ground problem as well.

Here is the Heartland engineering drawing showing how they wire the disconect switch from the factory. The important things to note is that when the switch is off, the truck can still charge the battery and, most importantly, the breakaway switch will still work.

It really doesn't matter. If you look at any service manual for anything with batteries, it will always tell you to disconnect the negative cable.

I to have my switch on the ground side. this is what most mechanics have told me

Everything I've seen in RV or Marine applications seem to have the disconnect on the positive side. Is there something different about marine or RV applications and/or wiring vs. automotive?

I had a look at the wiring diagram that Bob posted, and the factory uses the positive side as well. I'd love to understand why.

If you are removing a wire from the battery, remove the negative first. That way if the wrench hits the frame you don't short the battery as you could if you were removing the positive first.

Switches are generally in the positive side. Both in my boat and 5th wheel. But then in the boat it was used to connect one, both, or no battery.

When parked for a long time on shore power I usually disconnect 2 of the 3 batteries and cycle them including the truck that I seldom drive. The batteries all have a ground isolater that I bought at Wally World and I have a battery power extension that I sometimes plug the truck in to keep the batteries fully charged if I don't use the truck for extended time.

My friend has an SOB unit with a positif Battery isolator and blew up one of his batteries while switching it on. So far we have not been able the find the problem other then the power converter also blew at the same time. Very expensive occasion that we cannot explain.

wyleyrabbit said:

Everything I've seen in RV or Marine applications seem to have the disconnect on the positive side. Is there something different about marine or RV applications and/or wiring vs. automotive?

I had a look at the wiring diagram that Bob posted, and the factory uses the positive side as well. I'd love to understand why.

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I have read all the responses and I guess I'm still confused. Like wylerabbit, I too don't understand why RVs and boats seem to always use the positive side. I have always disconnected the negative terminal on autos or equipement that needed to be stored for any length of time.

It seems to me that someone mentioned on this forum something about arcing when throwing the switch that could harm appliances etc.

So at this point I'm still not sure what is the correct method and why it's the correct method.

You should unhook the positive on Auto's also

With regard to arching, connecting or disconnecting either terminal in an otherwise continuous circuit will draw a spark.

I will guess that with our common dc circuits being negative ground systems, disconnecting the positive terminal keeps the ground side negative. Disconnecting the negative terminal makes the ground side positive. I don't have an answer for the followup 'So what?'. Accessories/devices are wired to the positive side and then connected to a convenient ground. I suppose the disconnect switch could be considered a device and gets wired into the positive side. I prefer having both a positive and a negative busbars for connections instead of depending on the chassis for ground path.

Battery disconnects go on the positive side as close to the battery as possible.
With some switches you find may have a "field disconnect" That is for use in a automotive style charging system. The basic switch is the same and can be used.

Higher quality switches will have a make before break connection. This will keep your circuit live while you switch between 1-2 or both. Meaning that if battery #1 is connected and you switch to battery #2, #1 will not be disconnected until the connection is made with #2

If just disconnecting the battery for maintenance or repairs etc, the negative comes off first. Prevents you from causing a direct short with a wrench while removing the positive. Negative is last on for same reason.

Remove The Negative Cable First,
Re-connect The Negative Cable Last:
Why? Because the wrench or socket is touching the live part of the electrical connector. There is a good chance that the wrench or socket handle will accidentally touch something. The entire car is connected to the negative terminal.
If your wrench is on the positive terminal and it accidentally touches anything metal, you will short circuit the battery. The voltage isn't harmful, but the sudden unexpected sparks will startle the **** out of you, and could even burn you. There is so much current (amperage) available that your wrench literally becomes an arc welder.
If you disconnect the negative cable first, and reconnect it last, then the car is not electrically connected to the negative battery terminal. After that you can disconnect the positive battery terminal with minimal risk, because if your wrench touches any metal parts of the car there is no complete circuit, and nothing happens. The only risk comes from touching the other (i.e. negative) battery terminal.
While connecting or disconnecting the negative cable, you don't need to worry about the wrench touching metal parts of the car, because everything is at the same electrical potential. You only need to keep the wrench from touching the positive battery terminal. That's easy.

caissiel said:

When you boost a car with jumpers or booster cables the ground is what is the most dangerous connection.

The batteries will blow up with ground problem as well.

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Either connection can be dangerous. It is best to not connect to a batteries post when jumping if possible.
The ground lead should not be attached to the battery.

Jump start:
positive to dead battery positive post
positive to booster positive post
Negative to booster negative post

Last connection and the one that can cause your problems;
negative to an unpainted frame or bolt (dead battery). This keeps any potential sparks away from the battery.
Some vehicle (trucks) may have separate posts just for this.

After jump - reverse the process.

Batteries "blowing up" are rare.
I have seen at least a half dozen blow the top off in my career. Including a 36 volt forklift battery.
I have seen 2 blow up in the face of the mechanic - not a pretty sight.

BTW - batteries going dead because they are left on a concrete floor is an old wives tale.

Your instructions about the sequence of connecting positive and negative battery cables when jumping a dead battery are the same as those instructions which come with every set of jumper cables sold by automotive parts retailers.

All great information.

So? What's the consensus? On an RV, should the battery disconnect be on the positive side (as Heartland and other mfgrs do)? Or should it be on the other side?

wyleyrabbit said:

So? What's the consensus? On an RV, should the battery disconnect be on the positive side (as Heartland and other mfgrs do)? Or should it be on the other side?

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porthole said:

Battery disconnects go on the positive side as close to the battery as possible.

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Duramax1 said:

Your instructions about the sequence of connecting positive and negative battery cables when jumping a dead battery are the same as those instructions which come with every set of jumper cables sold by automotive parts retailers.

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Never bought cables from a retailer and never read any of those instructions.

Who reads instructions anyway?

Once one side is disconnected whether it's the Pos. or Neg. side...the battery is out of the equation. Really won't make any difference electrically. I like what Porthole has to say and totally agree...Don