The Siemens SENTRON 5SL6440-7MB is a 4-pole miniature circuit breaker (MCB) with a C tripping characteristic, rated 40 A and a breaking capacity of 6 kA per EN 60898 at 400 V AC.
Four poles in a single 72 mm wide housing (4 modular width units) — that is 4 x 18 mm per pole, the standard DIN-rail pitch. The sealable design allows panel builders to lock the toggle position after commissioning.
Sourcing and BOM fit
For a panel originally specified around the 3-pole 5SL4363-7, note the width difference: the 4-pole variant takes 72 mm (4 MW) versus 54 mm (3 MW) for the 3-pole, so a DIN-rail section that had room for a 3-pole plus a spare module may need a wider rail or a different layout. The 5SL4363-7 also carries a 10 kA breaking capacity per EN 60898, so if the fault level at the board exceeds 6 kA, the 5SL4363-7 is the correct choice.