What this MCB does
The Siemens 5SY5104-6 is a 1-pole miniature circuit breaker from the SENTRON series, rated 4 A with a B tripping characteristic. It breaks fault currents up to 10 kA per IEC/EN 60898-2 and UL1077, so it clears a short circuit before downstream wiring or equipment takes thermal damage. The single modular width (18 mm) snaps onto a DIN rail via the quick-assembly system and occupies one slot in a distribution board — no extra space for neutral switching, since this pole does not switch the neutral conductor.
B-curve tripping and thermal derating
The B characteristic trips between 3 and 5 times rated current — the standard choice for resistive and general-purpose loads where inrush is modest. At 35 °C ambient the breaker holds 4 A continuously; at 40 °C it derates to 3.76 A, at 50 °C to 3.5 A, and at 60 °C to 3.22 A (–). That derating curve means a panel running at 50 °C ambient should treat this as a 3.5 A device, not 4 A, to avoid nuisance tripping on a warm bus.
Mounting and integration
The 5SY5104-6 mounts in any position on a DIN rail. Installation depth is 70 mm; overall depth is 76 mm. Combined terminals at top and bottom accept wiring without reorienting the breaker. The housing is halogen-free and silicon-free — relevant for panels in clean rooms or environments where outgassing must be minimized. Sealable with a lockable cover if the specification requires tamper-proofing. Pollution degree 3 and overvoltage category III suit it for fixed installations inside an enclosure, not for wet or outdoor locations (IP20 only with connected conductors).