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Quick Blog about the FIA spec Battery Isolator's

Brent Peters Battery Isolator CAMS FIA

We’ve done a couple of YouTube videos about them but thought we’d go to print about their use and why they’re needed in your track car.

In basic terms the FIA spec isolators are a normal battery isolator switch with an additional two contacts, one normally open, one normally closed.  These contacts serve two very important purposes. To kill the engine and give the electrical system a safe discharge to earth/ground.

This is the key thing to understand, in an emergency you need to not just isolate the battery but kill the engine as well – most people get this wrong and use a normal battery isolator. With these they just isolate the battery.  When the engine is running and you isolate the battery the electrical system is going to keep going being supplied from the Alternator, then once you stop the engine the alternator has nowhere to discharge its power as it spins down creating a spike that can damage electrical components.

The officials at the track are well trained and there to respond in an emergency – if you are unfortunate enough to have an accident and your unresponsive the officials know to hit the isolator to kill the car. If your isolator just cuts the battery and the engine keeps running on pumping oil everywhere or worse fuel its not going to end well.

How do the 2nd contacts work?  

Contact two is on (closed) when the main switch is on – This can be used to switch the power supply to the ignition system (coil in a carby set up) or ecu.  When I wire these switches up I use the contact two in line with the feed to the relay switching the ecu, some people use it for the relay to the fuel pumps. I recommend against this as in an emergency or engine run on scenario there’s enough fuel pressure (or fuel in the carbie) to continue to run for a few seconds or more – in a fire these valuable seconds can be the difference between being able to put a fire out and losing the car or worse.

Contact one – is off (open) when the main switch is on, what you do with this is run a wire from the main power supply out of the main switch (not the battery side) through contact one and then to ground via the supplied 3-ohm resistor.  What this does is give the electrical system a small load path to ground to safely discharge the power from the alternator and rest of the electrical system as it spins down and is isolated from the battery. This works in the same way as the safety surge arrestor on jumper leads.  With out this there can be voltage spikes and surges that can damage the alternator and worse I have seen hi end ECUs damaged from not doing this.


These isolators are the cheapest and easiest way to isolate and kill your engine meeting CAMS/ ANDRA rules. there are some other great isolators out there that also do this with the same principle – Cartech do a solid state relay version which is expensive but a very very nice unit and for the remote switching removes the need for a cable to run the 2nd outside isolation point needed for racing category’s.

I really hope this helps clear up some of the info out there on these and helps. Please post up and tag us in your set ups or if you have any questions,  

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