Good question. The logic I would use behing a cutoff would be on the + side. That creates a total diablement of the electrical system anywhere after the cutoff. If you used the - side, areas of the electrical system could energize if they were supplied a ground. (Keep in mind that this is a what if condition.)
One advanage I THINK would be behind the neg mount cutoff is a reistance issue. Again, I THINK that it would create more resistance breaking the + side, but you would need to confirm it with someone that knows a little more about electritity.
Yes, good question. I originally chose the + side but ended up on the - when the cut-off I purchased would not fit well on the positive side. It fit perfect on the negative side so there it went. The terminals are different sizes.
The rule of thumb seems to be the neg side. Repair manuals always say to disconnect the negative battery terminal before doing electrical work. The electrons flow out the negative terminal (not sure what that matters, but it may start a fun argument )
I was always taught negative goes on first and off last.
Therefore, I would assume that you disconnect the positive, that way a spark still has a ground circuit to ground, so to speak.
If you keep the positive connected you could still Zap yourself, or something else, for example if you were to complete the circuit with your finger, or any metal object (and possibly fry something)
A battery quick diconnect switch should be placed on the neg. side of the system.If it is put on the pos. side there is more chance of a spark when switched on or off.I don`t mean to offend anyone here,but any shop manuals that I have read say to remove the neg. first and connect last,doing the reverse can cause a larger spark when diconnecting or connecting.
I also talked to my mechanic neighbor this afternoon and he said the same thing, put it on the negative side as there is less chance of spark. Doesn't seem to jive with what 4d noted but there ya go... I think I will move it over to the Neg.
I agree, What I meant was the negative should have the break, now that I read my note, it's sounds the opposite. Sorry about that. I was referring to when you connect the terminals neg on first and off last. That is how I was taught, many moons ago.
I was always taught the negative also. Flow is out the negative. I guess people think the positive is "hot", but I'd put it on the negative side. Same one you disconnect to work on the car.
Let's address the dangerous part first!The reason that the manuals (and most mechanics) say to disconnect the negative side first is that if/when the wrench you are using to loosen the clamp or bolt touches a metal part of the car, you won't short out the battery. Doing the same while removing the positive first would result in a direct short from positive to ground (zap/ka-boom!). For those who learned it the other way, now would be a good time to change! Those of you with Jags and other positive earth vehicles may continue to disconnect the positive first.
If you disconnect the positive, you could still short the battery by dropping a wrench across the positive post and any nearby metal part of the car, whereas with the negative cable off the only way to short the battery is by dropping the wrench on both top posts. Safer all the way around disconnecting the ground cable.
An interrupted circuit is an interrupted circuit, so a quick disconnect can go on either side of the battery, whichever is more convenient. That being said, the master switch on race cars is on the positive side and if wired correctly has a separate circuit for the alternator to completely shut off the car when it is running. If the vehicle is off, it doesn't matter, and I'm assuming that the cutoff is to prevent battery drain when sitting for a while, not to kill a screaming engine when the car is upside down!
That really makes no sense, as the battery will always be HOT while the NEG ground is connected. Anything touching the POS will cause a spark connection while the NEG is stilled grounded.
With the NEG disconnected, you can touch the POS all day and not cause a spark connection. The only way to dick that up is to have whatever is touching the POS to simultaneously touch another metal component and cause an arc.
Without a doubt, having the POS connection covered with a normal rubber battery boot, and having the NEG with the quick-disconnect is the safest choice. In my opinion.
'68 428 HO M3 Monster, 4-on-the-floor! Need I say more?
As Ponchoshop noted, racing applications have the master switch (not a quick disconnect but a high amperage switch) on the positive side, in an easily accessible location and well marked to allow someone (pit crew, fire or corner marshal, etc.) outside the car to cut the power in case of a crash or fire. Wired correctly, the engine will also be shut off and reduce the chance of fire or further damage. Wired incorrectly as I've seen quite a few, the alternator will continue to supply juice to the engine even though the positive lead has been effectively cut and defeat at least part of the purpose of having the master switch, that of shutting off the engine.
So it does make very good sense - for racing classes. It is a very important safety item that likely has saved many lives. Since you're not racing, do it the way that makes the most sense to you!
Négative side always off before the positif because if you disconnect positif with a wrench and you touch accidently the chassis you will make a short circuit wrench can pass easy 600 amps or more. same logic apply when you reinstall so you put négative last. So put your device on the négative!!!!!
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