User Manual

Description
2.3 Protection system
3WA Air Circuit Breakers
56 Equipment Manual, 05/2021, 92310000002-03
NOTICE
Damage to electronic trip unit (ETU) due to incorrectly dimensioned current sensor
The measuring input of the electronic trip unit is designed for a maximum ground fault
sensor secondary rated current of 4 A for 500 ms. This value must not be exceeded.
The selection of the current sensor must take into account the internal circuit breaker load
of 0.11 Ω.
The transformation ratio of the current sensor must be set on the ETU600 electronic trip unit.
This can be done on the display of the ETU600 electronic trip unit in menu item
5.3.6 Ground-fault current or with the SENTRON powerconfig configuration software.
GF mode
A ground-fault current can be calculated mathematically or measured directly. The three GF
modes available on the ETU600 electronic trip unit are described below.
GF Residual
The ground current is formed by the vectorial sum of the currents measured with the internal
current sensors and the external N-conductor sensor (N-CT). All four-pole circuit breakers
have an internal N-conductor sensor.
(1)
External N-conductor sensor (N-CT)