Thread: Master Battery disconnect

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Regarding the installation of a master battery switch should the switch be placed in the postive or negative current path of the battery. I have read a few post that suggest you are better off to open the ground side than the positive.

Any suggestion out there... Hot or Ground

Do it either way you like, but if you plan to compete at a NHRA track, the positive side of the battery goes through the switch.

Denny, I've asked the reason from several people in NHRA and I always get the same answer...."because that's what it says in the rulebook".....profound, hey?

Originally posted by DennyW


Tech, the hot by the rules, is that because if it made a ground, you would be in trouble ? And a ground would be easier to make than a hot ? Just wondering.

I' found most NHRA rules are aimed at "What can go wrong in the event of an accident". If you have both the battery and cut off switch (right by the battery) in the trunk that kills 99% of the circuit. if you cut the neg. side you'd still have a live circuit runing throughout the vehicle. Ground that circuit anywhere (In an accident) and you have a dead short. Bad Bad Bad.

Originally posted by DennyW
Ok, That's what I was thinking. Just wanted to make sure. Plus, we just gave 29arod a good reason.

Yup ..... we supply a copious collection of data.

All the sanctioning bodies specifie the ground on the hot side. A ground on the negative side would not be good for the reasons sited above, plus will not prevent parasitic drains on your battery from sources that are grounded to the chassis.

My son ''the electrician'' (Wired our house with ALL switches interrupting the positive side of the circuit . Doing anything other than that drew a ......."What da' heck do you think you are doing" ....... LQQk from him. HEHEHE

Originally posted by DennyW
Yes, on alternating current for residential, and factories, you always switch the hot side. That way, when you have a faulty ground, and it runs through you, you only get about 60 volts, instead of the full 120, hahaha.

Had a guy at Winnebago touch a hot 440 circuit on a stamping press one day. Only thing that saved him was his elbow was resting on the machine. Blew a hole in his elbow, but he lived to tell about it. Had the 440 gone through his body ...... he would have had a much worse day.

The reason you switch the positive, in all cases is so you won't electricute yourself. Even in a house you don't switch a ground, or neutral.

Think about it. If you switch the ground and accidently lean on the positive, "YOU" become the ground. If your standing in a puddle of water, you could feel the effects of a fully charged battery. Although it is only 12vdc it could over excite ones pace maker.

Just make sure all of your circuits are fused correctly.

Don't skimp on price. Go down a get one that is going to cost more then 40 greenbacks (buy USA ) and you will have a switch that will last forever.

Originally posted by 81fleetside
The reason you switch the positive, in all cases is so you won't electricute yourself. Even in a house you don't switch a ground, or neutral.

Switching a neutral on house current won't shut the light off. If it does somethingz' wired wrong. Switching the ground will. That's why inexperienced do-it-yourself-ers wire them that way sometimes. Won't pass code though.

Don't even get me started on what our house wiring looked like when we bought the place. First thing we did was start from scratch. The previous owner had solid core wire twisted and taped to multi-strand. Then a few feet further it would be lamp cord, then another short piece of something else. (And to make matters worse NO junction boxes at any of these splices). I think his motto was ......... if the light goes on ........ it must be right???

Oh Oh, back to the thread................ Positive side disconnect is a good thang'.

Do they put fuses in grounds? Do they switch a ground or neutral to your light?

No they don't.

You never switch a ground for safety reasons. If you disconected the ground and leaned up on the positive, it could make your "pace maker's" beat rate go into double time!

A 12 volt battery would not be life threatning (in most cases). Just don't be standing in a puddle of water with your new sneakers while disconnecting the rusted positive terminal with your bare hands.

Dont skimp on price either. Go out and buy an American USA brand, for a little more then 40 greenbacks and you will have a switch that will last a lifetime.

I would not even consider one of these devices for theft reasons. The criminals today can gain access to the most highly sofisticated alarm systems.

I never have used one, but the steering wheel device looks like it would be more then a petty criminal would want to deal with on a Saturday Night!

Wow! great response to my question! I will relocate the battery disconnect to the postive side..... Thanks for your opinions

Regarding prior post: Master battery disconnect.....

"There's considerable controversy over wether it's best too hook up the master shutoff("kill") switch to the positive or negitive side of the battery. As far as I know, NHRA rules mandate connection at the positive side. However most stock car sanctioning bodies require installing the kill switch on the negative side and for good reason. It's much safer to route the negative cable through the main battery disconnect. If you through the positive side, the exposed terminals on the back of the switch could contact the body metal during a crash. The negative cable connects to the body ground already, so it doesn't matter if it touchs. www.mercurycapri.com/technical/electric/ks.html "

with the big alt. and a computer car putting it in the neg. wire makes more sense. its to easy to spike the computer or another part of the IE. ive did both, but the word ground has taken on a new meaning with the late model cars. JMO