Description
2.6 Protection system
3VA molded case circuit breakers
78 Manual, 04/2015, A5E03603177010-02
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 I
N
refer to the current setting value; the associated setting time is identical to t
r
.
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.
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