Ask an expert

Are jumper leads are all the same?

Jason

From the "Ask Jack" archives - 29 August 2008

No, quite often you get what you pay for.

In many cases the cheaper leads are okay, particularly if they're being used to start the average petrol engine vehicle and are not in constant use.

The problems arise when these leads are used to start a diesel or a high capacity large petrol engine, or are used on a regular basis.

We're assuming that the jumper leads we're talking about are identified as being spike protected. Simply put, this helps prevent damage from a power surge in voltage when the leads are disconnected, which can cause damage to components such as on-board computers and alternators. We're also assuming the user knows how to connect and disconnect them correctly. If in doubt, don't try to jump start a vehicle - ring the AA!

Many people gauge the strength of jumper leads by the thickness of the cables. The danger here is sometimes the insulation makes up the bulk of the cable, leaving a very thin amount of cable core to carry the current from the donor to the flat battery. Have a closer look at where the cable core is secured to the jumper lead clamps. Firstly look for a good connection, and there should be a reasonable amount of core cable in relation to the total cable thickness. Poorly crimped connections can fail if the jumper leads are in regular use, as the angle of the cables when connected can cause the inner core to work loose. Diesel engines operate on a much higher internal compression ratios, so more electrical load is placed on the cables in comparison to an average-size petrol engine. The thinner-cored jumper leads can suffer from sever overheating, and in most cases the amount of current flow is insufficient to boost the flat battery.

While your jumper leads may be adequate for your needs, be careful when offering to assist fellow motorists, especially if they're driving diesel or large petrol-powered vehicles