What snaps onto a 60 mm busbar and reverses a 15 kW motor?
The 3RA2220-4ND27-0AP0 is a Siemens SIRIUS reversing starter — a factory-assembled combination of two contactors, a mechanical interlock, a thermal bimetal overload relay, and a circuit-breaker, all pre-wired on a common S0 frame that snaps directly onto a 60 mm busbar system. The supplied contactor 3RT2027-1AP00 and link module 3RA2921-1AA00 form the reversing pair with a mechanical interlock that prevents both contactors from closing simultaneously — a requirement for any reversing application where a phase-to-phase short on the motor terminals would otherwise occur.
Busbar mounting and panel clearance — the S0 frame dimensions
The unit is designed for snapping onto 60 mm busbar systems, not for DIN rail — the fastening method is a dedicated busbar adapter (supplied as 8US1251-5NT10,) that clips onto the busbar and receives the starter. Dimensions are 260 mm height, 90 mm width, and 155 mm depth. The vertical mounting position is mandatory — horizontal mounting would require derating the thermal overload because the bimetal element's trip curve shifts with orientation. Clearance requirements: 50 mm upwards, 32 mm forwards, 10 mm downwards, 10 mm at the side. Backwards clearance is 0 mm — the unit sits flush against the busbar backplane.
Trip Class 10 and thermal bimetal overload — what it means for motor protection
The overload release is thermal bimetal with a Class 10 trip characteristic. The short-circuit trip is magnetic, provided by the integrated circuit-breakers 3RV2021-4NA10 — these handle the instantaneous magnetic trip for bolted faults, while the bimetal handles overloads. The two protection functions are independent but share the same S0 frame. Operating temperature range is -20 to +60 °C with temperature compensation active across that same span — the bimetal element's trip point is corrected for ambient temperature changes, so the motor protection stays accurate whether the panel is in a cold warehouse or a warm machine room.
The supplied sub-components (contactor 3RT2027-1AP00, link module 3RA2921-1AA00, busbar adapter 8US1251-5NT10, circuit-breakers 3RV2021-4NA10, and RS assembly kit 8US1250-5AT10) are all current-production Siemens catalog items — no risk of a single component going EOL and stranding the assembly.