What it is and what it does
The Siemens 5SL4520-8 is a SENTRON 5SL4 miniature circuit breaker (MCB) rated 20 A with a D tripping characteristic, designed to protect branch circuits against overloads and short circuits in residential and light commercial infrastructure. It is a 1P+N unit — switching the live pole and switching the neutral — rated 230 V AC (250 V AC in single-phase operation), with a 10 kA breaking capacity per both EN 60898 and IEC 60947-2. The D curve means the magnetic trip fires at 10–20× In (200–400 A instantaneous), sized for loads with high inrush like small motors, transformers, or discharge lighting — not for general-purpose or resistive circuits where a B or C curve would be the standard choice.
What the ratings mean for fit
20 A continuous rating and 10 kA SCCR at 230/250 V AC define the fault-clearing capability. Energy limiting class 3 means it restricts let-through energy during a fault — less stress on downstream wiring and connected equipment compared to class 1 or 2 breakers. The 1P+N configuration with neutral switching is common in single-phase final subcircuits where isolating both poles is required by local wiring rules; the neutral pole is not overcurrent-protected, only switched.
Mounting and wiring
Snap-on mounting to 35 mm DIN rail, occupies 2 width units (36 mm). Installation depth 70 mm, overall depth 76 mm — fits standard distribution boards with adequate knock-out clearance. Screw terminals accept 0.75–25 mm² solid or stranded copper; tighten to 2.5–3 N·m. Mounting position any orientation; ambient range –25 to +55 °C, storage –40 to +75 °C. IP20 with conductors connected — suitable for enclosed distribution boards only, not for wet or dust-exposed locations.