Siemens 5SU1354-3KK20 — SENTRON RCBO, 20 A, B-Curve, Type F
The Siemens 5SU1354-3KK20 is a 2-pole RCBO from the SENTRON series, combining overcurrent protection with residual current detection in a single 36 mm wide, 2-module-width unit. It is rated 20 A at 30 °C with a B-curve tripping characteristic and Type F residual current sensitivity, making it suitable for circuits supplying frequency-converter-driven loads or other equipment generating mixed-frequency leakage currents. The breaking capacity is 10 kA per EN 60898 and 20 kA per IEC 60947-2, giving the buyer two coordination paths depending on the standard the panel is designed to.
Ratings and what they mean for fit
The 20 A rating at 30 °C is the headline figure, but the derating curve matters more for a warm panel: at 40 °C the continuous current drops to 18.8 A, at 50 °C to 17.4 A, and at 70 °C to 14.6 A. If your enclosure ambient runs above 40 °C, the BOM current must be checked against the derated value, not the 30 °C number. The B-curve (3–5× In magnetic trip) is standard for residential and commercial lighting and socket-outlet circuits; it avoids nuisance trips on modest inrush from small motors or capacitive loads. Type F residual current detection is the key differentiator here. It responds to AC, pulsating DC, and mixed-frequency fault currents up to 1 kHz, which covers the leakage profile from single-phase VFDs, washing machine drives, and LED drivers. Standard Type A RCDs can miss high-frequency components; Type F catches them, so this RCBO is the correct choice when the load side includes frequency converters or switched-mode power supplies that generate smooth or high-frequency residual currents. The Super resistant K design indicates enhanced immunity to surge currents and voltage transients, reducing the risk of nuisance tripping in industrial environments with frequent switching events or lightning-induced surges. This is a robustness feature, not a rating change — the breaking capacity and trip curve remain as listed.
Mounting and integration
The 5SU1354-3KK20 snaps onto a 35 mm DIN rail per EN 60715, occupying 2 modular width units (36 mm). Installation depth is 70 mm, overall depth 77 mm — check gland plate clearance if the panel is shallow. The supply cord can enter from either top or bottom, and the device can be mounted in any position, which simplifies layout in crowded enclosures. Touch protection is built in, and the IP20 rating applies once the distribution board is installed with connected conductors.
Compliance and documentation
The RCBO is halogen-free and silicon-free, which matters for clean-room or high-reliability installations where outgassing or silicone contamination must be avoided. It carries the SENTRON brand designation and is classified per IEC 81346-2 and DIN EN 61346-2 as function F (protection device). Overvoltage category III and pollution degree 2 cover fixed-installation mains supply in industrial and commercial panels.