What function does the neutral wire serve in a four wire unbalanced wye system?

Answer 1

Answer for USA, Canada and countries running a 60 Hz supply service.

The neutral, by definition, carries the unbalanced load back to the source of power. The neutral carries the unbalanced load, meaning the amps on one leg that are greater than the amps on any other leg, back to the generator or transformer that supplies power to the whole configuration.

(Just a point of education) That means that when we have a 2 wire circuit with one hot black wire and one white wire we call the neutral, the white wire is not technically a neutral. There is no unbalanced load in a simple 2 wire circuit. The white wire is technically the "grounded conductor"; the black is technically the "ungrounded conductor". This is important because the code makes the distinction. So understanding this principle is necessary to understanding the code.

An example of a four wire unbalanced wye system is a commercial 480v 3 phase oven with associated lights, timer, and clock. The 3 phase oven operates very efficiently without a neutral. But very often, any associated lights, timer, and clock run on 277 volts supplied by just one leg of the 3 phase system. This creates the unbalanced load. The only amps on the neutral in this scenario are the amps used by the lights, timer, and clock.

You cannot safely supply this appliance without a neutral. This is a hypothetical scenario that is intended to help you understand the circuitry.

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As always, if you are in doubt about what to do, the best advice anyone should give you is to call a licensed electrician to advise what work is needed.

Before you do any work yourself,

on electrical circuits, equipment or appliances,

always use a test meter to ensure the circuit is, in fact, de-energized.

IF YOU ARE NOT ALREADY SURE YOU CAN DO THIS JOB

SAFELY AND COMPETENTLY

REFER THIS WORK TO QUALIFIED PROFESSIONALS.