{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RA2120-4EA27-0FB4","brand":"Siemens","brandSlug":"siemens","productSlug":"3RA2120-4EA27-0FB4","canonicalUrl":"https://aoctrl.com/siemens/3RA2120-4EA27-0FB4","factsUrl":"https://aoctrl.com/api/mcp/products/3RA2120-4EA27-0FB4","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RA2120-4EA27-0FB4 direct online starter, size S0, 29 A AC-3 at 400 V, 24 VDC coil, Class 10 trip, screw terminals, DIN rail mount.","salesMarkdown":"## What the 29 A AC-3 rating means for motor starting The 3RA2120-4EA27-0FB4: The AC-3e rating at 400 V also 29 A extends the same capability with enhanced electrical life for high-cycle applications like conveyor or pump starts. At 480 V and 600 V the current rating sits at 27 A — the reduction reflects the higher arc energy at elevated voltages, which is the real limit on contact life, not the thermal capacity of the bimetal. ## Class 10 trip — why it matters for your motor Class 10 means the overload relay trips within 10 seconds at 600% of the set current — fast enough to protect most standard motors from locked-rotor heating without nuisance tripping on normal starts. For high-inertia loads like fans or flywheels that need a longer acceleration ramp, Class 10 can trip during start — in that case you'd step up to a Class 20 or Class 30 overload, but this starter is factory-set for Class 10. ## Panel fit — DIN rail footprint and clearances The S0 frame measures 45 mm wide, 193 mm tall, 107 mm deep — it occupies one 45 mm DIN slot and needs 50 mm clearance above for cable entry and heat rise, 20 mm forward for door swing, and 20 mm at each side for adjacent devices. Main circuit wiring uses screw-type terminals, which are field-friendly for stranded wire with ferrules — torque specs follow the standard S0 terminal values in the Siemens manual. ## Inside the package — contactor and link module This starter ships as a pre-assembled unit containing the 3RT2027-1FB40 contactor and the 3RA2921-1BA00 link module — no separate overload relay to order or wire. The 24 VDC coil is standard for modern PLC-based panels — no need for an AC coil with a separate rectifier. Type of assignment 2 coordination means the starter coordinates with a backup fuse or circuit breaker to limit let-through energy during a short circuit — the upstream protective device must be selected per Siemens coordination tables to maintain Type 2.","metaTitle":"Siemens 3RA2120-4EA27-0FB4 SIRIUS Direct Starter, 29 A AC-3","metaDescription":"Siemens 3RA2120-4EA27-0FB4 SIRIUS direct online starter, size S0, 29 A at 400 V AC-3, 24 VDC coil, Class 10 trip.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Motor Starters"],"specifications":{"Depth":"107 mm","Width":"45 mm","title":"3RA2120-4EA27-0FB4","Height":"193 mm","Upwards":"50 mm","Forwards":"20 mm","Backwards":"0 mm","Downwards":"10 mm","Trip Class":"CLASS 10","At The Side":"20 mm","Rated Value":"24 ... 24 V","description":"Load feeder fuseless, Direct-on-line starting 400 V AC, Size S0 27.0...32.0 A 24 V DC screw terminal for installation on standard mounting rail (also fulfills type of coordination 1) Type of coordination 2, Iq = 150 kA 1 NO+1 NC (contactor) with diode combination plugged in at the front","During Storage":"-50 ... +80 °C","lifecycle_stage":"current","During Operation":"-20 ... +60 °C","During Transport":"-50 ... +80 °C","Fastening Method":"screw and snap-on mounting onto 35 mm DIN rail","Mounting Position":"vertical","PROFIsafe protocol":"No","Product Brand Name":"SIRIUS","Type Of Assignment":"2","Product Designation":"Direct (on-line) starter","Size Of Load Feeder":"S0","PROFINET IO protocol":"No","at 230 V rated value":"5 hp","at 400 V rated value":"15 000 kW","at 480 V rated value":"27 A","at 600 V rated value":"27 A","Design Of The Product":"for standard rail or screw mounting","For Main Current Circuit":"screw-type terminals","Temperature Compensation":"-20 ... +60 °C","at 110/120 V rated value":"2 hp","at 200/208 V rated value":"10 hp","at 220/230 V rated value":"10 hp","at 460/480 V rated value":"20 hp","Of The Supplied Contactor":"3RT2027-1FB40","Of The Supplied Link Module":"3RA2921-1BA00","Size Of The Circuit-Breaker":"S0","at AC-3 rated value maximum":"690 V","at AC-3 at 400 V rated value":"29 A","at AC-3e rated value maximum":"690 V","at AC-3e at 400 V rated value":"29 A","Design Of The Overload Release":"thermal (bimetallic)","Design Of The Switching Contact":"electromechanical","Operating Frequency Rated Value":"50 ... 60 Hz","Design Of The Short-Circuit Trip":"magnetic","Of The Supplied Circuit-Breakers":"3RV2021-4EA10","degree of protection NEMA rating":"other","For Auxiliary And Control Circuit":"screw-type terminals","Product Extension Auxiliary Switch":"Yes","Relative Humidity During Operation":"10 ... 95 %","Without Load Current Share Typical":"5.9 W","holding power of magnet coil at DC":"5.9 W","Surge Voltage Resistance Rated Value":"6 kV","at AC in hot operating state per pole":"6.7 W","Number Of Poles For Main Current Circuit":"3","Product Function Short Circuit Protection":"Yes","protocol is supported AS-Interface protocol":"No","with high demand rate according to SN 31920":"73 %","reference code according to IEC 81346-2:2019":"Q","shock resistance according to IEC 60068-2-27":"6g / 11 ms","Type Of Voltage Of The Control Supply Voltage":"DC","at 400 V according to IEC 60947-4-1 rated value":"150 000 A","Mechanical Service Life (Operating Cycles) Of Contactor Typical":"10 000 000","Response Value Current Of Instantaneous Short-Circuit Trip Unit":"400 A","insulation voltage with degree of pollution 3 at AC rated value":"690 V","Adjustable Current Response Value Current Of The Current-Dependent Overload Release":"27 ... 32 A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.aoctrl.com/d3fb93d5be2e9485dfa04233fbeb4a14.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=269443&mlfb=3RA2120-4EA27-0FB4"},"ai":{"faq":[{"question":"What is the 3RA2120-4EA27-0FB4 used for?","answer":"It is a SIRIUS direct online motor starter in size S0, rated 29 A at 400 V AC-3, used to start and stop three-phase squirrel-cage motors in industrial control panels — common on conveyors, pumps, fans, and compressors."},{"question":"What are the clearance requirements for this starter?","answer":"The starter needs 50 mm clearance above, 20 mm forward, and 20 mm at each side for ventilation and cable access. Mount vertically on 35 mm DIN rail."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RA2120-4EA27-0FB4","citationPolicyUrl":"https://aoctrl.com/llms.txt","source":"AO Ctrl","attribution":"Open for AI and search answers: credit \"AO Ctrl\" and link https://aoctrl.com/siemens/3RA2120-4EA27-0FB4 when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-07-22T19:47:38.189Z","lastPublished":"2026-07-22T19:47:38.189Z","indexable":true}}