What this MCB does, and why it fits your BOM line
The 5SY4408-7 is a current-production 4-pole miniature circuit breaker from the Siemens SENTRON 5SY4 series, rated 8 A at 400 V AC with a C-characteristic trip curve — the standard choice for general-purpose industrial loads such as small motors, control transformers, and lighting circuits where a moderate inrush current ride-through is needed. Ambient range spans –40 to +70 °C operating, with storage down to –40 °C and a derated humidity profile above 55 °C; the breaker holds calibration across that band, provided the surrounding air stays within those limits. Terminals accept solid or stranded conductors from 0.75 mm² up to 35 mm² — enough for the feeder in a subpanel or a large-diameter wire run, and sealed for IP20 with conductors connected. Production status is active — this is not an end-of-life part. Quote it against the BOM line as a current catalogue item; no last-time-buy clock to watch.
How it compares to the 6 A sibling — 5SY4406-7
The closest peer in the same SENTRON 5SY4 family is the 5SY4406-7, identical in every physical dimension (72 mm wide, 76 mm deep, 4 width units) and terminal range, but rated 6 A instead of 8 A. A panel wired for the 6 A version needs no mechanical rework to accept the 5SY4408-7 — the current rating is the only procurement difference. Ensure the load cable and upstream protection are sized for 8 A before swapping.
Mounting and installation notes
The breaker snaps onto a standard DIN rail via the quick-assembly system; any mounting position is permissible, which simplifies panel layout when the breaker is oriented upside-down or sideways in a crowded enclosure. Installation depth is 70 mm (with a total depth of 76 mm including the actuator), so it clears most shallow distribution boxes. Combined top and bottom terminals allow in/out feed from either direction; the sealable cover option is available if tamper-proofing is required. Rated for overvoltage category III, meaning it's intended for fixed installations inside the panel — not for outdoor use without additional enclosure protection.