Why is the negative side of a battery grounded when it’s the source of electrons?

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I’m trying to understand the reasoning behind grounding the negative side of a battery in vehicle electrical systems, given that the negative terminal has an abundance of electrons. In electron flow theory, electrons move from the negative terminal (where there is an excess of electrons) to the positive terminal (where there is a deficit of electrons).
If the negative terminal is the source of electrons, why do we consider it a “sink” and connect it to the chassis ground? Wouldn’t it make more sense to ground the positive side, which is where the electrons are flowing to?

Additionally, I’m interested in learning about the thought process and design principles that electrical engineers follow when making this decision. What are the safety, performance, and practical implications of grounding one terminal over the other?

In: Physics

5 Answers

Anonymous 0 Comments

In an electric circuit the battery doesn’t “send out” electrons. The electrons already exist in the entirety of the circuit and the battery is just using energy to make the electrons contained in all of them circulate. Think of it as a chainsaw where the electrons in the entire circuit are the chain and the battery is the motor. 

Using the negative terminal of the battery as a reference point or ground just makes the math easier. At the end of the day what matters is what is your current return path and that’s taken into consideration when choosing where to ground your device.

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