Description
2.3 Protection system
3WA1 air circuit breaker
Equipment Manual, 02/2023, 92310000002-06
59
Implementation on the circuit breaker
For direct measurement of the ground-fault current, an external current transformer
(GF-CT) can be connected to terminals X8-11 and X8-12 of the secondary disconnect
terminal of the circuit breaker.
The current transformer must have the following properties:
• Primary rated current I
pr
= 150 A to 2000 A
• Secondary rated current I
sr
= 1 A
• Accuracy class 1
Damage to electronic trip unit (ETU) due to incorrectly dimensioned current
transformer
The measurement input of the electronic trip unit is designed for a maximum current of
4 A over 500 ms. This value must not be exceeded.
The selection of the current transformer must take into account the internal circuit
breaker load of 0.11 Ω.
Note
Proper operation of the external current transformer is not monitored by the ETU600
electronic trip u
nit.
The transformation ratio of the current transformer must be set on the ETU600
electronic trip unit. This can be done in menu item 5.3.6 Ground-fault current using the
operating keys on the display of the ETU600 electronic trip unit or with the help of the
SENTRON powerconfig configuration software.
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