I just added a circuit to my breaker box and it got me thinking about how the wiring all works. The neutral and ground both go to the bad bar in the circuit box, if they’re both in the same place then why can’t that just be wired inside the outlet and a single wire runs the length instead of two?
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In North America the power comes into your house as 240 volts carried on two live or hot wires. If you need 240 volts only you don’t need a neutral. Air conditioners for example generally only have two hot wires as they only need 240 volts. Many other appliances such as ranges will have the 240 volts and a neutral. This allows for both 240 volts (live to live) and 120 volts (live to neutral) to be available at the appliance.
Since most of the circuits in your house are 120 volts, it is provided by one live hot wire (typ. Black). But to complete a circuit you need a path back to the source. This is provided by the neutral (typ. White). The neutral can be considered as a center tap between the two hot wires provided by your utility. By doing this you end up with 240 volts from hot to hot, but 120 volts from hot to neutral. You should now be able to appreciate that the neutral is actually a current carrying wire.
The ground wire is a safety wire and is intended to only carry current in the case of a short circuit. If you use it as a neutral (bad idea) it becomes current carrying. This is not what you want.
The neutral is tied to ground at the panel to give you a zero reference. Voltage is a differential between two points. The neutral being tied to ground gives you the base reference.
Another poster stated that in much of the world, the neutral is not tied to ground at the service panel. In these cases it is very likely that the working voltage for the residence is 240 volts, not 120 volts.
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