What this RCCB is and what it does
The Siemens SENTRON 5SM3644-4 is a 4-pole residual current circuit breaker (RCCB), type B, with a short-time delayed characteristic. It is rated 40 A at 400 V AC, with a 300 mA residual operating current. The short-time delay means it tolerates brief inrush or transient leakage without tripping — useful on circuits with connected electronics or motor drives that produce a short-duration ground-leakage pulse. Type B detection covers AC, pulsating DC, and smooth DC fault currents up to 1 kHz, so it is the right choice for variable-frequency drive outputs, UPS systems, and PV installations where pure AC-sensing RCCBs would be blind to DC fault components.
Key ratings and what they mean for fit
The 10 kA short-circuit current rating (SCCR) means this device can safely interrupt a fault up to 10 kA without welding contacts or rupturing the case — that covers most commercial and light industrial panelboards fed by a transformer of 500 kVA or less. The 0.8 kA rated conditional short-circuit current per EN 60898 and IEC 61008-1 applies when the RCCB is backed by an upstream overcurrent device; that coordination figure is what you use for selectivity studies. The 4-pole design (3 phases + neutral) handles three-phase loads with a monitored neutral, typical for 400 V distribution in European-style panels. Mounting is snap-on DIN rail (REG profile), and the unit occupies 4 modular width units (72 mm). It can be installed in any position, which simplifies layout in crowded enclosures. The IP20 rating applies with the distribution board installed and conductors connected — standard for enclosed panel mounting, not for exposed outdoor use. Ambient range is -25 °C to 45 °C operating, with storage down to -40 °C. The device is silicon-free, which matters for applications like automotive paint lines or semiconductor fabs where silicone outgassing can cause adhesion or contamination issues.
Panel integration notes
Snap-on DIN rail mounting (REG profile). Installation depth is 70 mm, so it fits standard 80 mm deep enclosures. The 72 mm width (4 MW) matches the modular grid; leave one MW gap on each side for heat dissipation if the panel is densely packed. Supply can enter from top or bottom — the SIGRES function (switched-off state indication) works only with bottom feed. Supplementary devices (auxiliary switches, shunt trips, alarm contacts) can be added on the right side via the product extension feature. Power loss is 1.1 W per pole at rated current — negligible for thermal budgeting in most panels, but worth summing if you have 20+ units in one enclosure.