What this 63 A C-curve MCB does in a panel
The Siemens 5SY3263-7 is a 2-pole SENTRON miniature circuit breaker rated 63 A at 400 V AC, with a C-curve tripping characteristic that means it holds through mild inrush (5–10x rated current) and trips fast on hard shorts — the standard choice for motor-starter feeders, lighting sub-circuits, and general distribution where you don't want nuisance trips from transformer or capacitor inrush. Breaking capacity sits at 4.5 kA per EN 60898 and 6 kA per IEC 60947-2, with a 5 kA rating under UL 1077 / CSA C22.2 No.235 — enough for most commercial and light-industrial panelboards where the available fault current stays under those numbers. The 2-pole format (2 width units, 36 mm wide) mounts on a DIN rail via the quick-assembly system, installs in any position, and accepts solid or stranded conductors from 0.75 to 35 mm² at both top and bottom combined terminals.
The 63 A C-curve is the headline: C-curve trips magnetically between 5 and 10 times rated current, so a 63 A breaker holds a 315–630 A inrush before instantaneous trip — right for motor feeders and transformer primaries. If your load is purely resistive (heaters, lighting), a B-curve sibling would give tighter protection, but for mixed loads this is the standard. The 4.5 kA per EN 60898 is the domestic/commercial rating; the 6 kA per IEC 60947-2 is the industrial rating — the breaker is certified to both, so it fits either spec environment. The 15 kA DC rating per IEC 60947-2 (at 72 V DC max) is worth noting if you're using it in a DC sub-distribution board.
Integration notes
DIN-rail mount via quick-assembly system — snaps on without tools, clips off with a screwdriver. Sealable with a lead seal or sticker — useful for utility metering or rental panels where tamper evidence is required.