What the ratings mean for fit
The Siemens SENTRON 5SL4540-8 is a 2-pole (1P+N) miniature circuit breaker with a D tripping characteristic, rated 40 A at 30 °C and 230 V AC. The D-curve means it tolerates high inrush currents — typical for motor, transformer, or lighting ballast loads — without nuisance tripping. Breaking capacity is 10 kA per EN 60898 and IEC 60947-2, so it safely interrupts faults up to that level in residential or infrastructure panels. The 1P+N configuration switches both line and neutral, with the neutral pole switching but not protecting — a common arrangement for single-phase final circuits where neutral isolation is required.
Thermal derating and ambient conditions
Rated current is 40 A at 30 °C ambient. At 40 °C it derates to 37.89 A, at 45 °C to 36.8 A, and at 55 °C to 34.47 A. If your panel runs warm — say, above 40 °C — factor that derating into the load calculation. The breaker is rated for ambient temperatures from -40 °C to +75 °C, with max 95% humidity at 55 °C. Pollution degree 2 and overvoltage category III suit it for standard residential and light commercial distribution boards.
Mounting and integration
The 5SL4540-8 occupies 2 modular width units (36 mm) on a DIN rail, with an installation depth of 70 mm and overall depth of 76 mm. Mounting position is any, and the enclosure is IP20 with connected conductors — standard for inside a distribution board. Touch protection is built in, and the breaker is sealable for tamper-proofing. Halogen-free and silicon-free construction is noted for environments sensitive to outgassing.