If we have AC Current coming into our homes, then why we have different coloured wires?



If we have AC Current coming into our homes, then why we have different coloured wires?

In: Physics

Safety and speed. If I see a green or bare wire, it’s a ground. If I see a white or grey wire, it’s neutral. Anything else is “live.” This all assumes that the wiring has been done to code. [**See here**](https://www.thespruce.com/electrical-wire-color-coding-1152863#electrical-cable-and-wire-color-markings) for more info.

Power coming into houses in America comes in on 3 wires. A neutral, and 2 hot wires. The 2 hot wires are 180° part meaning when one wire is at the peak of it’s 120 volts the other wire is at -120 volts. Tying these two together in a circuit allows you to provide power for high power devices like air conditioners, car chargers, hot water heats and electric stoves. Typically the hots come in on a red and black wire while the neutral comes in white and ground is either green or bare copper.

Because one of the wires is at the same potential as ‘earth’ or ‘ground’, and you want to know which one that is. Technically you could touch the neutral wire with one hand and for example a metal pipe in your house with the other and nothing would happen.

If you do the same with the other (hot) wire, you’d get shocked. Light switches for example are supposed to switch the hot wire, not the neutral one, because otherwise a light fixture that’s turned off at the switch would still potentially be dangerous to work on.

The core idea here is that voltage is always relative. If you take an AA battery and you touch the negative terminal of it to a metal pipe in your house, then the positive terminal of the battery is now at +1.5V relative to the (earthed) pipe. But if you touch the pipe with the positive terminal instead, the negative terminal would be at -1.5V relative to the pipe and earth.

The fact that it is AC means the current is flowing back and forth, and this often creates the confusion which is the source of your question. If the current is going both ways, why does it matter which wire is which.

The answer is that the power is coming from the black wire. The easiest way to think about it is a spring. If I hold one end of a slinky and tie the other to the wall, and I push and pull it, the wires go back and forth – but all the power is coming from the end I am holding.