Neutral Protection

Presentation

A long-time overcurrent protection function is dedicated to the neutral protection.

Availability

Neutral protection is available on:

MicroLogic 2.0 B, 5.0 B, and 6.0 B trip units
4-pole circuit breakers

Description

Where the cross-sectional area of the neutral conductor is at least equivalent to that of the phase conductor, and the current in the neutral is expected not to exceed the value in the phase conductor, it is not necessary to provide overcurrent protection for the neutral conductor.

The neutral conductor must have protection against overcurrent if:

The cross-sectional area of the neutral conductor is less than the cross-sectional area of the phase conductors
Non-linear loads generating third order harmonics (or multiples thereof) are installed

MicroLogic B trip units are suitable for the following protection types.

Possible types	Neutral protection
4P, 3D	Off
4P, 3D + N/2	Half neutral
4P, 4D	Full neutral
P: Pole, D: Trip unit, N: Neutral protection

NOTE: With the 4P 3D setting, the current in the neutral must not exceed the rated current of the circuit breaker.

Operating Principle

Neutral protection has the same characteristics as phase protection:

Its pickup is proportional to the long-time protection pickup Ir.
It has the same tr time delay values as long-time protection.
Its short-time and instantaneous protections are identical.