Over Current Relay

<...what is the difference between "residual current" and "neutral Current"?...Over Current...>

Neutral current is the negative vector sum of all the phase currents. It indicates the state of balance between the phases and any single phase loads that they may be supplying at any instant.

• If all three phases were in balance and there is no residual current, the neutral current is zero.
• If only one phase is supplying loads and there is no residual current, then the neutral current equals and is opposite to the phase current.

Both of the above are entirely normal.

Residual current is the vector sum of all phase currents and the neutral current. It indicates that current is flowing to the earth conductor via a fault and can be used to disconnect the circuit so as to save lives from being electrocuted.

• If the residual current is less than the setting of its circuit protection device then there is no need to disconnect the circuit.
• If the residual current exceeds the setting of its circuit protection device, then the device operates so as to disconnect the circuit from the supply so as to minimise the risk of electrocution.

Overload current is that which exceeds the trip setting of a different circuit protection device. In overload, the circuit is in a fault condition that cannot be withstood without damage, which includes destruction of the facility by fire, for any significant length of time. The device operates so as to disconnect the circuit, thereby minimising the risk of fire.

Does that help?

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