What is the difference between neutral and ground in a three phase system?

Answer 1

No matter whether we're describing a three-phase service or a a single phase service, the bare copper "earth" or "ground" wire normally carries no current. Its purpose is to provide an emergency path for current if ever there is any accidental contact between a hot wire and the external (or internal) metal parts of any electrical device which a user may be able to touch. The electrical device can be a motor, a water heater, an air conditioner unit or any other kind of appliance.

By carrying away the excess current in a fault condition - which should cause the protecting fuse to blow or the circuit breaker to trip - the "ground" or "earth" wire protects the building and its occupants because the power should be cut off before anyone gets electrocuted or any overloaded circuit wiring or appliances catch on fire.

The neutral is the normal "return" wire. In systems where the load is supplied from only one hot (or "live") wire, the neutral completes the circuit and carries current back from the load to the power station. In "Y-" or "star-connected" three-phase circuits the neutral doesn't normally carry any current if all three phases are properly balanced.

If the three phases actually have unbalanced loads - which can easily happen if each phase is being used to provide power to different single-phase circuits, each with their different loads - then some current will flow in the neutral wire and will result in unbalanced 3-phase currents flowing back to the power station.

All the neutral and ground (or "earth") wires in a building are tied or linked together at the incoming service main breaker panel. This is the only place they should ever be tied together because it is "upstream" of all the fuses and/or circuit breakers protecting the hot (or "live") wires for the various circuits installed in the building.

Warning: we must never assume that a neutral is safe to touch: it has to be checked with a voltmeter or a voltage indicator to be sure it is not "live". This is because a neutral wire is designed to carry current under normal circumstances.

So, if a neutral wire going back to the incoming main breaker panel has not been properly connected - or suffers a deliberate disconnection or some accidental damage which causes it to break - then it and any neutral wires connected to it further downstream will go live up to the break because of being connected to the downstream loads which still have hot feeds coming into them!

That is why we should never use a neutral as a substitute for a proper, separate, ground or "earth" wire.

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If some external accidental damage or electrical breakdown of the wiring's insulation occurred anywhere to the house wiring, to a socket outlet or to an appliance, these things could be very dangerous if there was no such protective wire.

For example, if there was no protective ground or earth wire, a fault could happen that is of a kind which did NOT draw enough extra current to blow a fuse or make the main circuit breakers on the incoming supply panel "trip" to cut the current off - but the wiring could still catch on fire and/or someone could be electrocuted!

Neutral wires are the return paths to the power generation station for current it supplies to the house or building via single live or "hot" wires in the branch circuits.

For more information please click on the Related Questions below.

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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.

Answer 2

The neutral is a live conductor intended to allow the flow of current from the load . An earthing conductor is intended to allow the flow of current in fault conditions only when a metal part ( not part of the electrical system eg a metal handle on a cooker ) becomes live .

Answer 3

well first of all we must understand difference between neutral and ground (earthing in some cases, but preffered as grounding when it is on any other planet than earth).

neutal is provided in any system to complete the circuit or to run the device we are connecting it to.

the ground is provided for protection purpose in case of motor or electrical device rises to potential ,it can harm the operator of it so we provide the ground wire to it (with lower resistace than human body obviously) thus making it possible to flow the current through it in case the outer body of motor rises to a potential and saving operator.

In a 3 phase system (say star or Y connected) the mid point is the point which should have no potential at all in a balance system so a wire is provided from it to carry out the current in case of unbalancing of system .

the grouding (earthing in some cases) dictated earlier is called equipment grounding while which discussed in later part is known as system groundig.

Answer 4

Phase and neutral are both conductors. The load circuit receives (so to speak) power from the phase conductor, and returns (so to speak) power back to the neutral conductor. In this fashion, a complete series circuit is formed between the distribution power transformer, the load, and the two conductors connecting them.

The only difference between phase and neutral is that neutral is grounded at the distribution panel. This is a single point ground so, technically, no current flows on ground. The purpose of the ground is to place a limit on the voltage present at any point of the circuit with respect to ground, and also to be able to detect and protect against a ground fault.

Answer 5

The neutral conductor provides a return path for single-phase loads and you would expect to find neutral current flowing as a normal condition.

The ground conductor provides a return path for fault current when a hot conductor accidentally comes in contact with a grounded object. This is a safety feature of the wiring system and you would never expect to see grounding conductor current flow during normal operation.

At one point in the wiring system, the neutral conductor and the ground conductor are connected together, but they still serve different purposes.

Answer 6

In a three phase power system, ground is at ground voltage, and the neutral, depending on whether it is grounded or not, may or may not be at ground potential (it may be "floating").