The Siemens SENTRON 5SL1240-6MB is a 2-pole miniature circuit breaker rated 40 A with a B tripping curve, designed for 230/400 V AC residential and infrastructure circuits. Its 3 kA breaking capacity per IEC 60947-2 covers most domestic and light commercial fault levels — enough for a sub-distribution board feeding general-purpose socket outlets and lighting, but not for high-fault industrial switchgear where you'd step up to a 10 kA or 25 kA rated device.
The 40 A rating on a B-curve means the magnetic trip activates at 3 to 5 times rated current (120–200 A), which suits resistive and general-purpose loads like heaters, lighting, and socket circuits — not motor starts that draw higher inrush. At 2 modular width units (36 mm wide), it occupies the same DIN-rail footprint as any standard 2-pole MCB.
Snap-on DIN rail mount, any position. Ambient range -40 °C to +75 °C covers unheated utility rooms and roof spaces; the 3.4 W power loss per pole at rated current is negligible for panel thermal budgeting in a standard enclosure.