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Description

2.6 Protection system

3VA molded case circuit breakers

Manual, 04/2015, A5E03603177010-02

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

for the set delay period t

The S release operates according to a characteristic with a current-dependent curve I

t. The

electronic trip units ETU 5-series and 8-series can be optionally switched over to a current-

independent tripping characteristic.

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" (ground fault).

The G protection 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

for the set delay period t

Ground-fault protection can be implemented as a current-independent and a current-

dependent function (I

t).

On 4-pole molded case circuit breakers and 3-pole molded case circuit breakers with

external current transformer for N conductor, the G protection calculates the vector sum of

the currents of the three phases and the neutral conductor. The G release trips the breaker

or an alarm is issued via the communication system if the rms value of this vector sum

exceeds the set trip value I

for the duration of the set delay t

Siemens 3VA1 100 A User Manual

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