What it is and what it does
The Siemens 5SL6240-7 is a SENTRON miniature circuit breaker (MCB) — two-pole, C-curve, rated 40 A with a 6 kA breaking capacity per both EN 60898 and IEC 60947-2. The C-curve (tripping between 5× and 10× In) is the standard choice for general-purpose loads: lighting, socket circuits, small motor starters, and distribution subfeeds where inrush isn't extreme. The 6 kA rating at 400 V AC means it safely interrupts a fault up to that level without upstream damage — adequate for most residential and light commercial panelboards. Rated for 50/60 Hz, overvoltage category III, pollution degree 2.
Panel fit and mounting
Snaps onto standard DIN rail, any mounting position. Occupies 2 modular width units (36 mm wide), with a depth of 76 mm and 70 mm installation depth behind the panel. IP20 with connected conductors — fine for enclosed distribution boards; not rated for washdown or outdoor exposure. Sealable (padlockable) for lockout/tagout. Halogen-free and silicon-free construction, so it won't outgas corrosive compounds in sensitive environments.