What it is and what it does
The Siemens 5SL3403-7 is a SENTRON 5SL miniature circuit breaker (MCB) with four poles, a C tripping characteristic, and a 3 A rated current at 400 V AC. The C-curve means it trips between 5 and 10 times rated current — standard for protecting inductive loads like small motors, lighting ballasts, and distribution sub-circuits where inrush isn't extreme. Breaking capacity sits at 4.5 kA per EN 60898 and IEC 60947-2, which covers most residential and light commercial panel fault levels in 400 V three-phase networks.
Fit and panel integration
Four width units (72 mm wide) on a standard DIN rail. Installation depth is 70 mm; overall depth with terminals is 76 mm. Terminal blocks accept solid or stranded copper from 0.75 to 25 mm², with a tightening torque of 2.5 to 3 N·m. Mounting position is unrestricted, and the housing is IP20 with conductors connected — standard for enclosed distribution boards. The breaker is sealable, halogen-free, and silicon-free, which matters for panels in clean-room or food-processing environments where outgassing is a concern.