Why doesn't current flow through the neutral to earth?

Answer 1

The 'hot' wire delivers current from the power station into the load, which could be any electrical appliance such as, for example, a fridge, a light or a motor.

The 'neutral' wire is there for the specific purpose of carrying the current coming out of the load back to the power station. If the neutral wire was not there, there would not be a complete electrical circuit from the source (power station) to the load and back to the source.

In normal operating conditions the connection from the neutral wire to the Earth does not carry any current.

There should always be 0 V (zero volts) between the neutral wire and the Earth. i.e. no potential difference should ever exist between the neutral wire and the Earth.

The "neutral to earth" connecting wire is fitted to ensure that no part the neutral side of the circuit can develop a high voltage above Earth. If that connecting wire wasn't in place and the circuit had no other protection device (such as a GFCI or RCD) fitted, a very dangerous electrical shock hazard could be present which could electrocute the people using the appliance.

That is why any grounding wires, fitted either to the appliance or to the breaker box, should never ever be cut or removed.

Answer 2

Kirchoff's Current Law states that the signed sum of the currents entering a node is zero. If the neutral point is the node, then, in a balanced system, hot matches hot, resulting in no current through neutral. Any imbalance, either due to neutral to hot current flow that is not balanced by neutral to opposite hot current flow, or due to ground fault, will result in a current flow on neutral, so that the sum of zero is maintained.

When you think about this, remember that the law said "signed" and "entering". When you analyze a circuit, simply be consistent in your usage. For instance, in a balanced system, current entering the neutral node from one hot side is considered positive, and the current entering the neutral node from the other hot side is considered negative, i.e. it is leaving, not entering.

Ground fault will, of course, "change the rules", because you no longer have only three paths to that neutral point node. In fact, that is how ground fault current interrupters (GFCI's) work - they measure outbound current and compare it to inbound current - they must be equal and opposite, i.e. they cancel each other out - otherwise there is another path - a ground fault - and the device trips.

Answer 3

Unbalanced neutral current does not flow to earth unless in case when there is a neutral to earth contact on the consumer side of the supply.

In such case, the earth leakage protection unit will then be activated because there's an imbalance between the currents flowing through the three lines, of a three phase power supply, and the neutral. The imbalance come about because part of the neutral current is flowing back to the supply through the consumer earth continuity conductor. The sum of currents flowing to the consumer must be equal to the sum of currents flowing back from the consumer.