The Siemens 5SL4120-6CC is a 1-pole miniature circuit breaker rated 20 A with a B-curve trip characteristic, breaking capacity of 10 kA at 230/400 V. This is the part that sits on the DIN rail in a distribution board, protecting a single-phase final subcircuit — lighting or general-purpose socket outlets — where the B-curve's magnetic trip threshold (3 to 5 times In) clears short-circuits fast enough to avoid nuisance trips from moderate inrush, yet still coordinates with upstream SENTRON selective main breakers.
RoHS-compliant since 01 June 2013, but the REACH candidate list declares lead (CAS-No. 7439-92-1) above 0.1% w/w — standard for alloyed terminals in this class.