The Siemens 5SY3040-7 is a SENTRON miniature circuit breaker in a 1P+N compact design, rated 40 A with a C tripping characteristic and 4.5 kA breaking capacity per EN 60898 at 230 V AC. It occupies a single width unit (18 mm) on standard DIN rail, with a 76 mm depth that clears most 70 mm deep enclosures.
For a domestic or light commercial distribution board with a typical upstream transformer impedance, 4.5 kA is the standard domestic rating — sufficient for most final circuits. The 40 A rating on a 1P+N pole configuration means the neutral is switched alongside the phase, which is required in some regional wiring rules (e.g., UK, Australia) for single-phase final circuits.
Snap-on mounting to standard DIN rail (35 mm). The 18 mm width (1 MW) and 76 mm depth fit a standard 70 mm installation depth enclosure. Mounting position is any — horizontal, vertical, or flat — so it can be oriented to suit the panel layout. The top and bottom terminals are not combined (separate line and load connections), which is typical for 1P+N MCBs. Touch protection is provided on the terminals. The neutral conductor is switched internally, so no separate neutral bar connection is needed downstream of the breaker.
Vibration resistance tested per IEC 60068-2-6. Energy limiting class 3 means it limits let-through energy effectively for downstream equipment protection. The mechanical service life is 4,000 switching cycles typical.