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Neutral conductor protection (N)

The ID letter for neutral conductor protection is "N".

The neutral conductor protection system protects the neutral conductor against overloads and short circuits.

The letters IN refer to the current setting value; the associated setting time is identical to tr.

NOTE

A neutral conductor with full cross sectional area (distributed neutral conductor of the same size as the phases) is normally protected by the phase protection system and does not require separate protection.

Neutral conductor protection

Neutral conductor protection must be implemented in accordance with the standards valid in the country of installation. Possible reasons for implementing neutral conductor overload protection are:

  • The neutral conductor has a smaller cross section than the phase conductors.

  • Harmonic levels in the installation are expected to be higher than normal.

  • A large number of loads, or predominantly single-phase loads, will be connected.

  • The neutral conductor will be isolated for functional reasons, e.g. because there are several voltage sources.

  • The neutral conductor will be isolated for safety reasons, e.g. because work is in progress on disconnected units

Neutral conductor protection and 3VA2 molded case circuit breakers

The following versions of 3VA2 molded case circuit breaker have neutral conductor protection:

  • All 3-pole versions with external current transformer for N conductor

  • All 4-pole versions

Oversized neutral conductor protection can be implemented in combination with the electronic trip units ETU 5-series and 8-series. This might be necessary to provide protection against third-order harmonics and multiples thereof.

Parameters of the neutral conductor protection function

  • Tripping current IN:
    Adjustable as a proportion of the current setting (Ir) for overload protection

  • Tripping delay:
    Corresponds to the delay setting (tr) for overload protection

  • Tripping current of the short-time delayed short-circuit protection:
    Corresponds to the short-time delayed short-circuit protection (Isd)

  • Tripping delay:
    Corresponds to the delay setting for short-time delayed short-circuit protection (tsd)

  • Instantaneous short-circuit protection:
    Corresponds to the tripping current (Ii) for instantaneous short-circuit protection

Example of a neutral conductor protection characteristic

Adjustment of neutral conductor protection settings

The tripping current IN can be adjusted:

  • for ETU 3-series trip units via setting buttons

  • for ETU 5-series and 8-series trip units

    • via the buttons on the ETU display

    • via a PC using powerconfig

Response threshold of the neutral conductor protection

Response threshold of the long-time delayed protection

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N

Neutral conductor protection

1)

At rated operational currents In ≤ 63 A: IN = 40 % … 100 % In

2)

Applies to In > 63 A

3)

Dependent on circuit breaker size and rated operational current

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