The Siemens 5SM1742-6 is a 4-pole residual current circuit breaker (RCCB) from the SENTRON 5SM1 series, rated 25 A at 400 V AC with a 500 mA residual trip threshold — Type A sensitivity, so it catches pulsating DC fault currents as well as sinusoidal AC, which is what you need on circuits feeding single-phase rectified loads like switching power supplies or VFD auxiliaries. It snaps onto a DIN rail (4 width units, 55 mm installation depth), accepts top or bottom feed, and carries a 10 kA short-circuit current rating at 400 V — enough for most sub-distribution boards behind a larger upstream breaker. The 10 000 mechanical switching cycles typical service life means it will handle routine manual testing and infrequent fault clearing without wearing out early in a panel.
At 40 °C ambient the 5SM1742-6 carries its full 25 A rating without derating. At 45 °C it still holds 25 A. Above that the current tapers: 24 A at 50 °C, 23 A at 55 °C, 22 A at 60 °C, 21 A at 65 °C, and 20 A at 70 °C. The maximum permissible ambient is 60 °C; the minimum permissible is -40 °C.
Installation notes
Mounts in any position on DIN rail. The test circuit requires a minimum of 100 V to operate the test button. Silicon-free construction, size 1 per DIN 43880. Finger and back-of-hand safe touch protection on the terminals.