Description
2.5 Protection functions
3VA molded case circuit breakers with UL and IEC certification
Manual, 01/2019, L1V30435333-01
73
2.5.8
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 setting value of the current is designated with I
N
, the associated setting time is identical
to t
ld
.
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.
●
Higher harmonic components in the system can be expected.
●
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 3VA6 molded case circuit breakers
The following 3VA6 molded case circuit breakers have neutral conductor protection:
●
All 3-pole versions with external current transformer for N conductor (only with
ETUs 5-series and 8-series)
●
All 4-pole versions
The tripping systems of the ETUs 5-series and 8-series enable an overdimensioned neutral
conductor protection. This might be necessary to provide protection against third-order
harmonics and multiples thereof.
