Description
2.5 Protection functions
3VA molded case circuit breakers with UL and IEC certification
Manual, 01/2019, L1V30435333-01
71
Ground-fault detection in unbalanced systems
The neutral conductor current is measured directly and in the case of 3-pole molded case
circuit breakers only for the ground-fault protection, but in the case of 4-pole circuit breakers
the neutral conductor current is also evaluated for the neutral conductor protection.
The trip unit calculates the ground-fault current using the three phase currents and the
neutral conductor current for the vectorial summation.
For 4-pole molded case circuit breakers, the fourth current transformer is internally installed
for the neutral conductor.
3-pole molded case circuit breaker in unbalanced systems, 3-pole 3VA with external N
transformer:
Trip unit variants, 3-pole 3VA6 molded case circuit breaker with external N transformer:
● ETUs 5-series: ETU556 (LSIG alarm), ETU560 (LSIG)
● ETUs 8-series: ETU856 (LSIG alarm), ETU860 (LSIG)
4-pole molded case circuit breaker in unbalanced systems:
Trip unit variants, 4-pole 3VA6 molded case circuit breaker:
● ETUs 3-series: ETU330 (LIG)
● ETUs 5-series: ETU556 (LSIG alarm), ETU560 (LSIG)
● ETUs 8-series: ETU830 (LIG), ETU856 (LSIG alarm), ETU860 (LSIG)
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