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Description
2.6 Protection system
2.6.5
Short-time delayed short-circuit protection (S)
The ID letter for short-time delayed short-circuit protection is "S" (stands for "Short-time
delay"). The S function of the trip unit can be used to implement time-selective short-circuit
tripping in low-voltage networks in which multiple molded case circuit breakers are installed
in series.
The short-time delayed short-circuit protection function protects phases L1 to L3 and the
neutral conductor. The protection function responds if the current in at least one phase
exceeds the set tripping current I
The S release has a characteristic curve with current-dependent characteristic I
delay time is dependent on the energy content of the short-circuit current present. The ETUs
5-series and ETUs 8-series can be optionally switched over to a current-independent tripping
characteristic. In this case, a fixed delay time t
2.6.6
Instantaneous short-circuit protection (I)
The ID letter for instantaneous short-circuit protection is "I" (stands for "Instantaneous").
This short-circuit protection function protects phases L1 to L3. The instantaneous short-
circuit protection function responds if the instantaneous value equal to the rms of the current
in at least one phase exceeds the instantaneous tripping current I
2.6.7
Ground-fault protection (G)
The ID letter for ground-fault protection is "G" (stands for "ground fault").
The G release detects residual currents between phases and grounded, electrically
conductive parts. The ground-fault protection function responds if the ground fault current
exceeds the set tripping current I
Ground-fault protection can be implemented either as a current-independent or a current-
dependent function (I
On 4-pole molded case circuit breakers and 3-pole molded case circuit breakers with
external current transformer for the N conductor, the G release calculates the vector sum of
the currents of the three phases and the neutral conductor. On 3-pole molded case circuit
breakers, the vector sum is calculated without the neutral conductor. The G release trips the
circuit breaker, or an alarm is issued via the communication system if the rms value of this
vector sum exceeds the set response threshold I
76
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for the set delay time t
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3VA molded case circuit breakers with IEC certificate
Manual, 03/2019, A5E03603177010-03
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