Why do we need to attach one negative cable to bare metal when jumping a car?
In: Engineering
The best answer is a combination of AndMarmaladeSkies and TheDevler: modern cars are all negative grounded, which means the negative terminal of the battery is connected to the metal chassis. When boosting a car, it’s possible that a spark could ignite gases from the battery. So, to be safer, you make the final connection somewhat away from the battery, ie, on the metal chassis. This prevents you from doing the connection at the battery itself, where there is a tiny risk.
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