What gauge are jumper cables generally used for cars?
4 Answers
Small cars use 16 square millimeter copper cables, trucks use 25 square millimeter copper cables, and heavy trucks use 35 square millimeter copper cables. Since starting the engine requires high current and the battery voltage is low (resulting in even higher current), jumper cables should have as little resistance as possible. Below are the steps for using car jumper cables: 1. Clamp the red cable to the red positive terminal of the "dead vehicle's" battery. 2. Clamp the other end of the red cable to the red positive terminal of the "rescue vehicle's" battery. 3. Clamp the black cable to the black negative terminal of the "dead vehicle's" battery. 4. Then clamp the black cable to the black negative terminal of the "rescue vehicle's" battery. (If the negative terminal of the rescue vehicle's battery is connected first, the dead vehicle's negative terminal must not be connected to the battery's negative terminal but should instead be connected to the car body or grounded). 5. Start the engine of the "rescue vehicle" first, then start the engine of the "dead vehicle." If the dead vehicle still fails to start, check if there is poor contact in the metal connections. After successfully starting the engine, remove the jumper cables in the correct order to avoid potential short circuits.
I always keep a set of 25 square millimeter jumper cables in my car. Over the years working as a mechanic, I've seen too many incidents of smoke caused by using undersized cables. For regular sedans, the starting current is around 200 amps - 25 square millimeters is barely adequate but somewhat marginal, especially during winter when the battery condition is poor. If you drive a large-displacement SUV or diesel vehicle, it's more reliable to go with 35 square millimeters directly. The key factor is copper core purity - some cheap products with copper-clad aluminum simply can't handle high currents. Remember to choose all-copper clamps with large contact surfaces, otherwise the instant heat during startup can even melt plastic handles.
Last time I helped my neighbor jump-start their car, I did some research on this. The repair manual states that the minimum should not be less than 16 square millimeters, but in practice, I found this to be the bare minimum. From my experience, it's best to choose cables of at least 25 square millimeters, and keep the length under 3 meters—otherwise, the resistance becomes too high and affects performance. What amateur users often overlook is the quality of the clamps. Those thin metal clamps sparked as soon as they made contact, which scared me into switching to thicker copper clamps. Also, in winter, I recommend using 35-square-millimeter cables since the battery's internal resistance increases in cold temperatures, requiring stronger current.
As a veteran driver with 15 years of experience, I've gone through three sets of jumper cables. Now I exclusively use 30mm² pure copper cables with insulated sheathing - this wire gauge easily starts 2.0T engines. Don't believe those cheap sub-$10 cables online, actual measurements show they're not even 10mm². Pay special attention to the cable's flexibility - overly stiff wires tend to crack the insulation when coiled for storage. Always check the clamp spring tension before each use - rusted or stuck clamps can't properly grip battery terminals.
