The Siemens 5SY4540-6 is a SENTRON miniature circuit breaker (MCB) rated for 40 A at 230 V AC, with a B tripping characteristic and 2 poles configured as 1P+N. It's built for mechanical engineering and industrial panel environments, where the B-curve handles resistive and light inductive loads without nuisance trips from inrush. Breaking capacity sits at 10 kA per EN 60898 and 15 kA per IEC 60947-2 — the higher figure applies when the breaker is used as a standalone industrial device rather than a domestic consumer unit. That's the difference between protecting a sub-distribution board and a machine control cabinet. Mounts on a DIN rail via the quick assembly system, takes any mounting position, and accepts solid or stranded conductors from 0.75 to 35 mm² at the combined top and bottom terminals. The 36 mm width (2 width units) and 70 mm installation depth leave room for adjacent breakers in a crowded panel.
Lifecycle & sourcing
Halogen-free and silicon-free construction (cites:,) means it won't outgas corrosive compounds in a sealed enclosure — relevant for wind-turbine nacelle cabinets where condensation cycles are common.
What the ratings mean for fit
The B-curve trips between 3 and 5 times rated current — so 120–200 A magnetic release. That's a good match for resistive loads (heaters, lighting) and general-purpose circuits where you don't want the breaker to see motor inrush and drop a line. If your load has a high starting surge, a C-curve sibling would be the better call. Overvoltage category III means it's rated for fixed-installation distribution panels, not just socket-outlet circuits. The IP20 rating (with connected conductors) is standard for enclosed panel gear — no special sealing needed inside a cabinet. Ambient temperature range of -40 to +70 °C covers unheated turbine nacelles and outdoor industrial shelters. Storage range extends to -40 to +75 °C, which handles shipping through cold climates.