Monoposto Racing Forum

Hi all,

Can anyone tell me the correct size/grade of positive battery cable to use? I've found an intermittent connection in the wire from the master cut-out switch and the battery in the front nose and need to replace mine, I seem to think that the newer cables can be different ratings despite the physical diameter being the same? I wouldnt want to buy cable that cant carry the amps for starting etc.

Help greatly appreciated!

Matt.

I reckon the lightest duty starter cable on your local motor factors shelves will do fine. Prob about 8mm overall dia. Race cars are not churned over endlessly in freezing weather - and are usually started cold with a jump battery on separate wiring - so whilst you get a little voltage drop with a long run it will work fine. Do secure it carefully though as the insulation is not very thick & can chaff through where it goes through bulkheads etc. If in doubt replace the master switch as well - if you are not running an alternator you only need the simple type which just has the two big battery cable terminals

Thanks Dermot.

Matt,

Please see the technical document regarding "Cable Sizing" on the following page of our website http://www.formulafordzetec.co.uk/formu ... ec_025.htm The document gives suggested cable sizes for specified loads including those for starter / battery cables.

ALL CABLES should be measured by the cross sectional area of the conductor, (which in the case and most other cases will be copper), NOT the overall diameter which will include the insulation. Just to complicate matters, some cables of the same cross sectional area have different current carrying capacities due to the types / grades of insulation used.

When I rewired my FF1800, I'm almost certain I used 16mm2 cables, which is probably as light as you'll want to go (rated for 110A). But I've never encountered any problems. And unless you have a heavy duty starter motor I'd say you'll be fine with that.

I get all of my electrical bits from Vehicle Wiring Products Ltd ( www.vehicle-wiring-products.eu ) and they are very helpful. If you choose to go larger than 16mm2 the only issue you might have is attaching the terminals onto the cables as the bigger crimping tools are much more expensive. Alternatively cut them to length and take them to a garage and get them to do it.

Hope this helps

James

Just as a foot note to the above...

From an engineering perspective, it might be a good idea to consider a cable that can carry the same current (or greater) than the maximum your battery can deliver.

So, if you are running a Redtop 15 you'll want a cable that can carry 190A. Personally, in a racing application I wouldn't bother as you'll end up fitting massive cables that are difficult to work with and aren’t really necessary. But it’s worth thinking about!

And don’t forget your battery negative will want to be the same size the positive!!

Thanks for this info, I've gone for the same as you (110amps) is probably more than enough.

I rarely need to start the car without using the slave battery anyway so it was just getting the right size cable to the battery box as a precaution really.

Matt