Battery Disconnect , Positive or Negative ??

NHRA isn't the only racing organization that MANDATES a POSITIVE battery cable disconnect, - assuming NEG. ground -
SCTA - Southern California Timing Association - (Bonneville / El Mirage) also requires it.

As already said; unless you use a disconnect switch with provision for alternator - generator - shut-off, the engine will continue to run if the switch is used in EITHER side; and the disconnect switch is turned off while the engine is still running. (the alt./gen. continues to power the ignition)

Personally, of all the vehicles I have wired; I switch the POS.
Then a smaller wire - fused - to keep clocks, memories, etc.; powered if used.
(I did automotive wiring for a living)

With the available "boots" that can be used to cover the end of the battery cables and the terminals of the disconnect switch, I've never run into a "shower of sparks" situation.
No different than staying clear of the battery posts.

 

We cut the + side

 

I've done it both ways.. if your really concerned.. pull the cables off both sides..

my only suggestion is to NOT ever use one of these


over time it will corrode between the plates and cause a problem.. (ask me how I know)

for those who are concerned with "saving memory" (in my case to an ecm) speedway offers this neat little contraption..



basically its a nice little holder for a fuse (i didnt buy speedways, I built my own) anyhow.. when my master power switch is off.. the fuse allows a small amount of current to bypass and keep some accessory's powered up, BUT if i were to attempt to start the car, the fuse blows under the load.

which I like for theft protection too (both items are hidden)

 

If you use a reall "kill" switch it really does not matter what side you put it on. There are valid arguments for both but since you don't plan on racing there is no rule preventing you from putting it on the negative side. IF you do put it on the positive side you need to be sure that nothing can get to it and possibly short it out. You can also run a small fuse holder to jump the 2 terminals to provid power for a radio memory if that is desired and, as stated, if someone attempts to start the car the fuse will blow. If you are disconnecting the batery for storage safety and to keep it from running down over time just forget the switch and the radio memory since the radio memory is what kills most batteries during long term storage.

Another good thought for storage is abattery tender. They are pretty cheap and will keep the battery conditioned so when you do need it you just hook it up, turn the key and hit the road.


Happy motoring.

 

Nhra rules say it MUST BE on the Postive side .
That is wrong however . it should be on the negative side but they arent bright enuf to understand that.
When electricity was first discovered it was thought electrons flowed from positive to negative. About the time vaccum tubes for radios were developed it was discovered this was bunk and it actually flows from Negative to Positive. This is by the way very provable.
The first is called Conventional electrcal theory and belongs with the flat earth society and the theory of evolution. It is utter nonsense but is still taught because we dont want to let it go . It is because of that that NHRA has the Positive only rule.
The second is the Electron theory and states quite appropriatley that current or electrons flow from neg to positive.
It is correct.
I was caught by the NHRA electrical police n my own race car and finally had to change it if i wanted to race so i did begrudgingly.
In truth a fair way would be a rule that says battery current must be able to be switched off from outside the car by an external switch.
Theory aside if the current is off it is off period. but to do it right it should really be the neg side. Bottom line is it should not be in the rules , the only thing it should say is that a switch must be installed which interrupts the battery current.

 

Interesting thread ! I just read the SCTA rules for Bonneville section 3.K and they do not mention the side that the switch must be on. Just the fact that they must have one mounted and clearly marked etc.??

 

Ya got my vote !! Should be on the negative !!

 

Negative !!!!!

 

I put mine on the negative cable because it was closer to where I wanted to mount the switch behind my grille. I did it solely as a theft deterrent since racing or a low battery from sitting were not even a consideration.

 

But if the negative side of the battery isn't connected to ground, there is no circuit to short out....this would be like disconnecting your negative terminal & taking a screwdriver & "shorting" the positive terminal to the chassis - with the negative terminal disconnected, nothing will happen.

I don't have one on any of my cars, but if I did, it would be on the negative side. Not that it matters a lot, really...an open circuit is an open circuit.

 

Funny you should mention that... I shut off my positive power switch and the engine continues to run...!

 

Positive side as close to battery post as possible. Any short circuit in the system gets no power if the positive side is disconnected.

 

Sounds like half-n-half.
How about what Dejon Sanders said......gimme BOTH.
Install one accessible on the outside of vehicle connected to positive to satisfy NHRA and hide the negative disconnect near the battery. In storage or, if your parked and want to slow down a thief,switch off both switches. If your not concerned with NHRA hide both switches. If your running and have to kill the motor, hit the positive or external switch. Both switches off = absolute Isolation of all power from your ride. All this for an additional $20 switch.

 

If you guys check it out... Electrons actually flow from Negative to Positive.. Remember back in the day cars were Positive ground... If it is just a safety issue I would switch the ground.... Jason.

 

My vote is to go big...ever since caterpiller started using electric starters the battery switch has been in the negative cable..
any and all heavy equipment cuts the negative..
And i believe someone a whole lot smarter than me designed this system..
my vote is ..cut the negative...
any body want to debate another fun one? do you know that the ford starter solenoid is directional ? and has to be grounded to work properly?
dave ;-)

 

Well, first off, Fords have starter relays, no solenoids!

Seriously, define "directional" because I've damned sure hooked 'em up both ways & had 'em work....but not sure what you're saying here...

 

Disconnect both then you you`re definately gonna be right!lol.

 

All of our companies forklifts are on the ground side next to the battery.

 

I have mine on the positive side.

Why don't you just buy another switch and put one on both pos+ground?????????????????????

Then you won't have to worry

 

Working on heavy equipment , mostly CAT all use ground disconnects , your not running anything until the disconnect is turned on , yeah yeah yeah , its not a CAT heavy equipment forum , just putting my 2 c 's in . also i agree if storing car for the winter i trust no ground , but if ur racing follow NHRA rules . peace out bitches

 

...after 11 years.

 

POSITIVE!

 

Someone stated the SCTA says positive (+). That is not true. It states on page 46 in the 2017 rule book. "All vehicles shall be equipped with with a main battery disconnect switch. The disconnect switch or a positive mechanical control (cable or rod) for the switch shall be located at the front or rear of the vehicle, operable externaly and clearly marked. ".
Mines been on the negative since 1975.

 

I count 11 years.

 

Oops, you are correct!

 

From everything I have read here,there is no consensus.

I have always used the negative post for a battery disconnect while others prefer to use the positive post for the disconnect. HRP

 

The negative disconnects that I've seen don't fit on positive post terminals, they're too small.

 

I use them on the ground side. Why? Well, that's the way I have always done it. Not very scientific, I know.

 

Negative side


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As a couple of other guys already posted (a number of years ago) all heavy earth moving equipment have the battery disconnect on the ground side, this is the correct way to do it. As someone else posted above as well, electron flow goes from negative to positive. And finally, disconnecting the positive side is a real good way to get an arc, disconnecting the negative side is far less likely to arc, that's why you always pull the negative battery cable first when disconnecting a battery, and connect it last.

For those that argue that it won't kill the engine, it's a battery disconnect switch, not an emergency shut down switch, that is something else.

Bottom line, unless you're racing NHRA and have to have it on the positive side per their rules, put it on the negative side.