Neutral Protection
Presentation
A long-time overcurrent protection function is dedicated to the neutral protection.
Availability
Neutral protection is available on:
-
MicroLogic 2.0, 5.0, and 6.0 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 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 |
|
Operating Principle
Neutral protection has the same characteristics as phase protection:
-
Its pickup is proportional to the long-time protection pickup Ir.
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It has the same tr time delay values as long-time protection.
-
Its short-time and instantaneous protections are identical.
Setting the Neutral Protection
On four-pole circuit breakers, it is possible to select the type of neutral protection for the fourth pole using the three-position dial on the ComPacT NS circuit breaker:
-
Neutral unprotected (4P 3D)
NOTE: With the 4P 3D setting, the current in the neutral must not exceed the rated current of the circuit breaker. -
Neutral protection at 0.5 In (3D + N/2, factory setting)
-
Neutral protection at In (4P 4D)
-
Cover for neutral protection three-position dial.
Follow these steps to set the type of neutral protection.
-
Remove the cover of the switch.
-
Select the protection type.
-
Put the cover back in place.
Setting Values for Neutral Protection
The following table shows the setting values of the neutral long-time protection and pickup for the type of neutral protection selected:
|
Neutral protection type |
Neutral long-time pickup value |
|
|---|---|---|
|
OFF |
No long-time protection for neutral |
|
|
N/2 (factory setting) |
Ir/2 |
|
|
N |
Ir |
|