What is the purpose of the neutral conductor in a 3 phase/4 wire system?

Answer 1

It allows a single phase load to be connected.

The phase to neutral voltage is equal to the phase to phase voltage divided by the square route of 3. So for 480v, the phase to neutral is 277v. For 208V, the phase to neutral is 120v.

Answer 2

Actually, its 208 volts any phase to any phase and 120 volts any phase to neutral. If the only load is three phase balanced (i.e., a 3 phase motor) you don't need the neutral, but you should have a ground wire to the motor frame.

If you want to run 120 volt loads from any phase, you need the neutral.

Answer 3

I think you are asking if it is necessary in a three phase power system? Yes, it is still necessary. Just remember that each phase lead allows 120 volts for each lead-in, if you need 120 volts (house current) or 240 volts (dryer, electric heat), or 3-phase 3 X 120=360 volts (generator, welding, high-phase applications) , all still need the neutral.

Answer 4

Most three-phase systems power equipment at 220 volts - that's 110 phase 1 to 110 phase 2 (or 1 to 3, or 2 to 3). The neutral allows the same supply to power a 110 volt devices (phase to neutral). That's the fourth wire.