[ELI5] How do power lines work?


Recently I saw a power line with 2 wires (hold on). Only one AC power line and one ground wire on top. If I understand power correctly you need at least 2 wires to make a circuit and power stuff. Also another question, which wires on the power line do what?

In: Technology

4 Answers

Anonymous 0 Comments

I’m in the UK here, so my answers are biased towards our system. We have 3 pin mains plugs here, in a triangle. Bottom left is live, bottom right is neutral(also called return), and top is ground. The purpose of these three wires is as such:

Live and neutral are the current path for a circuit. There’s a potential difference (voltage) between them, and when you connect a load across them, current flows.

Ground serves as an emergency backup. If your device has a metal chassis, one potential issue arises if the case is ever accidentally shorted to the live wire. In this instance, the path of least resistance will be the body of the human touching it. To this end, the neutral wire is connected to the metal case, and if the live wire ever shorts to the case, current will flow from the live wire to the ground wire, away from the human.

The ground wire therefore serves as a convenient out-path for any stray electricity. your house will also detect an issue using an RCCB, which measures the difference between live and neutral current to detect stray current.

In the case of the cable you saw, I suggest it was probably not the live and ground cable, but the live and neutral cables. This is because the engineer designing the system decided it didn’t need ground protection.

I’m not sure what kind of cable you saw, if it’s an overhead cable, it didn’t need grounding because it’s difficult for a human to touch.

If it was an appliance cable, it didn’t have ground because the casing of the device is plastic and there was no way for a short to affect a human.

Hope this helps!

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