There’s jump leads, and then there’s jump leads

Posted on 02 Mar 2016 by

7am, it's raining, and you left the interior light on in the car, last night. So the battery is flat, but never mind, there's that pair of jump leads that came from the discount supermarket in with the spare wheel and ready to do sterling service. You open your bonnet, unravel the jump leads, try and reach them between your car and your wife's and...damn...they are only 3 metres long and the gap is 5 metres. So, you shuffle her car around, get them closer, the leads reach, you start her car engine and carefully connect the negative to one battery, then the negative to the other, then you repeat the process for the positives. You reach in to start your engine and...not enough beans to spin it over...but the supermarket jump leads are getting red hot, because they are made out of fairy light wire. 

Damn, again, but you were smart enough to buy your wife a pair of jump leads too, after all, they were only $49 a pair, so you get hers out, and double up, so now there are two leads between the positives and two leads between the negatives - surely that'll be enough.

Jump in your car, turn the ignition odd noise from the side of your engine bay...then nothing. At this point, you disconnect the leads (positives first, one end then the other, then repeat for negatives) and you call a taxi. You then call the car dealer, they send a tow truck and, when they get the car, they charge the battery and replace the computer which got fried when a huge voltage surge jumped between the cars and the supermarket jump leads didn't have anti-zap protection. 

So now you are down a few thousand dollars for a computer, towing, labour, taxi, dry cleaning, whereas spending $150 or so on a set of good leads would have made all the difference. 

So, why the difference?

Take a look at this image first of all - 3 sections of jump leads all rated around 200amp by their makers. The top one is from the maker that we like. The next two aren't. Copper is expensive, rubber isn't, so a feel of the cable size, alone, doesn't tell you much. It's all about how much HIGH QUALITY copper is in there (and, by the way, the bottom image isn't the worst that we've seen).

Next comes the antizap unit. The power running through jump leads during a tough start is colossal - think of enough to run 5 washing machines on their hardest cycle - so if there isn't an antizap unit then the chances of damaging sensitive electronics are high and, if there is an antizap unit, you'd have to hope that it wasn't made to the cheapest specification possible. 

Then the way the cables are connected to the clamps - high grade copper is useful for conductivity, but cheap steel is preferred by the budget players.

Then the clamps - need to be strong, resistant to warping, chemicals, acid, corrosion, with a hell of a strong spring to give a nice, tight, bite. Some are made of metal so soft that you could bite through them.

Then the length - a good set of leads will be 6 metres long, and 4 metres is the absolute minimum. 

A good set of leads looks like this:

A dodgy set of leads looks like this:

and this is a photo of a cross section of the dodgy one compared to proper cable of the same external dimensions. 















I made my own jump leads, because I needed extra long leads and they needed to be able to start anything, so the size of cable was all-important. To put it in perspective, they cost nearly $300 in materials, at trade prices. If I could have done it cheaper then I would, but then I know I'll need them.

The truth is that spending $50 or $75 on a set of leads is fine if they are never going to be used but, if you do need them, you'd be awfully glad if you spent $150, on something that'll last a lifetime.