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 Isd for the set delay period tsd.
The S release operates according to a characteristic with a current-dependent curve I2t. The electronic trip units ETU 5-series and 8-series can be optionally switched over to a current-independent tripping characteristic.