SENTRON T55 1-pole MCB, C-curve, 3 A
The Siemens 5SQ2170-0KA03 is a single-pole miniature circuit breaker from the SENTRON T55 series, rated 3 A with a C tripping characteristic. It breaks fault currents up to 3 kA per EN 60898 at 240 V AC, 50 Hz — the standard for final-subcircuit protection in commercial and light-industrial panels where the supply transformer impedance keeps prospective fault current below that level. The C-curve means the magnetic trip fires at 5 to 10 times rated current (15–30 A), so it handles the inrush of motor starters, contactor coils, and small transformers without nuisance tripping while still clearing a hard short. For resistive loads or long cable runs where inrush is lower, a B-curve sibling would trip faster; for high-inrush loads like welders, a D-curve would be a better fit. This one splits the difference for general mixed loads.