Master Cutoff Switch
 

After returning from a month "down South" working Div 2 races including both the Baby Gators and the Gatornationals I must comment on an important issue I found missing on a lot of racecars.

As stated in the 2019 NHRA rulebook, master cutoff switches MUST be clearly marked for the OFF position. That means both the left-right lever style and the push-pull type.

It would seem simple to turn the switch off if an incident happens on the track. But let's look at it a different way. After an incident on track the first person to arrive at the scene will turn the master cutoff switch to the off position. The second person arriving may not know that the switch has been turned off and turn it the other way which would turn the system back on. This can happen when the switch is NOT clearly marked.

The other one is the push-pull type. Everyone knows that push OFF is the way these switches work....or do they. Marking with a PUSH OFF label will assure that in an incident the power gets turned OFF. All it takes is for one person to pull the switch and the system is reactivated.

Marking your master cutoff switch is a simple yet very important way to let everyone know which way is OFF.

Re: Master Cutoff Switch
 

Thanks for the heads up Travis....that’s some valuable info right there....

Re: Master Cutoff Switch
 

It would only make sense for a push-pull type of lever to turn the power off when pushed, as in backing the car into a wall. But, common sense has not been too common for many, many years........

Any car I work on has that switch properly marked, I never want anything to happen to one of my friends or customers, as well as myself and family members driving one of our cars!

Re: Master Cutoff Switch
 

Rulebook states "push" must be the off action on a push-pull type mechanism. And most of the levers on switches I'm aware of go CCW to turn off if it's mounted that way. Also states it must be marked.

I'm a fan of having some type of secondary cable or other way of operating the master from the driver's seat, for both safety and convenience.

Re: Master Cutoff Switch
 

I have one in the car next to me that kills everything, just in case!

Re: Master Cutoff Switch
 

Ditto.

Re: Master Cutoff Switch
 

This Might be part of the problem, you get in an accident, shut your power off, first guy there thinks he’s turning it off and has turned it back on...
It should also be mandatory if you have one inside the car it moves the lever outside the car also, which I’m sure most people already do

Re: Master Cutoff Switch
 

The disconnect inside the car will not be affected by the outside disconnect being in the on position. The outside disconnect feeds the inside disconnect.














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Re: Master Cutoff Switch
 

When I had a push-pull system, I had a cable running from the trunk switch to a lever in the cockpit, Pushing the lever physically moved the rod on the back bumper. Since emergency persons are trained to move that switch, they could possibly turn the car back on. My current setup is a rotary switch on the back deck that cuts all power between the battery and the car. The power feed into the cabin is through a continuous duty Cole Hearse solenoid connected to an aircraft switch on the console to energize it. If something goes haywire I can slap that switch and kill all the accessories and ignition power. There is still one hot wire in the cabin (the battery cable) but the juice isn't going anywhere. It's a quick way of shutting off the ignition and fuel pump without flipping multiple switches.

Re: Master Cutoff Switch
 

If I have battery in stock location and add a second battery in back do I need a master cut off switch?
I think I don't but asking as I need to add a battery.

Re: Master Cutoff Switch
 

General: 8.4 Mandatory when battery is relocated or as outlined in Class Requirements.


Check the current class rules for your car. My guess is yes. Battery in trunk = rear deck mount cut off.

Re: Master Cutoff Switch
 

I thought that at first, but I'm not re locating. Just adding

Re: Master Cutoff Switch
 

Jeff,
You do need a cut off switch at the back of the car since you are putting a battery in the trunk.

Raul

Re: Master Cutoff Switch
 

It's just a switch.... Unless you are adding under the hood, put it in.


A stock battery location is under the hood. Install one anywhere else and a cut off would be required. When the battery is under the hood the power usually runs to a distribution block under the hood keeping the feed short and contained. When you add/relocate a battery in the trunk, you have 10-15 feet of vulnerable wire running under the car. The cutoff switch is meant to do two things, kill ignition and fuel pump power (fire control) and prevent any pinched or cut wire from shorting the chassis and blowing the whole friggin' car up with you inside.


Disclaimer: I am a bracket racer. I have a full cage, window net, neck collar and fire extinguisher in my 12 second car.



Anyone know the kill requirements for electric vehicles? Jeff Lane, you out there? I'd ask Garlits but I don't think he's around these parts much.

Re: Master Cutoff Switch
 

Yes! And if you want to wire this car "correctly" you will need a large constant-duty relay under the hood to disconnect the front battery from the rear switch........ Pain in the butt and extra cost, but well worth the hassle. I did an NHRA Stocker like this, the only "issue" is you need to remember to turn the main power off, especially after you put the car in the trailer. That constant-duty relay pulls a decent amount of power and will drain your batteries.........

Now, back to the battery location issue. I have a 2008 Buick Lucerne, stock battery location is under the rear seat. My 2015 Camaro has the battery in the trunk, from the factory, so do the newer Vettes.

These batteries are no relocated, wonder when the NHRA will start looking at these vehicles and making people put a switch in the rear of the car.

And what about those electric vehicles............

Re: Master Cutoff Switch
 

It's sort of a side step instead of a total thread derail, but I'm pretty amazed that no one seems to be concerned with batteries in electric cars.


Ever seen a vid on Youtube where some idiot shorts the battery of a vaping device and it goes into thermal runaway? Hellfire and carnage results.


Teslas use the same battery. But they have 8000 of them in their battery packs. Haven't heard a peep from the NHTSA, nor DOT for that matter.

Re: Master Cutoff Switch
 

I'll take a shot at answering the master cut off switch for electric vehicles question.. Jeff, team and I built the eCOPO as well as the orange car "Shock and Awe" that has run around division 6 for a few years.

All our cars, per General Rule 8.4, have master cut off switches. They are push off and clearly marked. When pushed they remove all low voltage power to the rest of the car (including to the low voltage components that connect the high voltage to the propulsion system).

We also have an "oh-sh#*" switch on the dash, that if ever needed (hasn't been needed in almost 175 electric runs) would remove 12v power to the master contactor in the hv motor system. That too is push off. That does not remove 12v power from the entire vehicle, just disconnects the HV.

Here's a picture of the back of the orange high school car.....
Pat

Re: Master Cutoff Switch
 

Thank you for the answer. In regards to the questions about EV cutoffs from others, the rule book has cutoff switch requirements. It must disconnect the motor and power pack. It's in the EV section buried up with ET Snowmobiles.

Re: Master Cutoff Switch
 

It is worth mentioning that the cutoff is supposed to be on the Positive side. If you have it the other way and crash and fold the quarter panel into the Negative terminal the switch won't work,
The rules are written in blood as they say.

Re: Master Cutoff Switch
 

I’ve decided to run a switch even though I don’t plan on putting a battery in the truck just yet.

My question is about the wire from the alternator, can it run to the battery or does it need to be run to the switch?

Re: Master Cutoff Switch
 

Coincidently, NHRARacer.com has a battery question this week. I never had or plan to have a car faster than 9.99 or 135 mph. but I never knew or even noticed that they apparently need a cut-off regardless of battery placement. External switch also?

http://www.nhraracer.com/content/gen...336&zoneid=132

Re: Master Cutoff Switch
 

probably need a cutoff like this one

Re: Master Cutoff Switch
 

Your alternator wire and battery cable should be on the same post on the switch. The other post on the switch will run the cable to your starter solenoid.

Re: Master Cutoff Switch
 

Travis, I’m guilty of not having mine labeled. Thanks for the reminder, I will address it.

Re: Master Cutoff Switch
 

I had a double pole Moroso to kill the alternator until a short at the starter burned it out. I replaced it with a single pole rotary at half the price wired like this and it works fine. No engine run-on.

Re: Master Cutoff Switch
 

This is the simple legal way to do it without extra wiring, solenoids, etc. You just have to be mindful that the alternator lead is always hot, and pay attention to making sure it is protected where it is routed and when working on the car..