{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RA2120-4NA27-0FB4","brand":"Siemens","brandSlug":"siemens","productSlug":"3RA2120-4NA27-0FB4","canonicalUrl":"https://aoctrl.com/siemens/3RA2120-4NA27-0FB4","factsUrl":"https://aoctrl.com/api/mcp/products/3RA2120-4NA27-0FB4","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RA2120-4NA27-0FB4 direct-on-line starter, Size S0, 28 A at 400 V AC-3, 690 V max, Class 10, 24 V DC coil, screw terminals, DIN rail mount.","salesMarkdown":"## SIRIUS S0 direct starter — what it is The Siemens 3RA2120-4NA27-0FB4 is a SIRIUS-brand direct-on-line starter in the S0 size frame. It ships as a pre-assembled unit: a 3RT2027-1FB40 contactor and a 3RA2921-1BA00 link module, ready to snap onto 35 mm DIN rail or screw-mount. The 24 V DC coil and screw-type main-circuit terminals make it a straightforward drop-in for a panel that already runs on 24 V control. ## AC-3 duty and trip class — what the ratings mean The 28 A at 400 V translates to about 15 kW (20 hp) motor full-load current, which lines up with the horsepower ratings Siemens publishes for this unit at 460/480 V. That's the standard for general-purpose motor starting — fast enough to protect the motor windings during a stall, but slow enough to let the motor accelerate a normal load. If your application has a long acceleration time (high-inertia fan or conveyor), you might need Class 20 or 30, but for most pump, compressor, and light conveyor work, Class 10 is the right call. ## Mounting and panel fit Mounts vertically on 35 mm DIN rail or with screws. The S0 footprint is 45 mm wide, 193 mm tall, 107 mm deep. Clearance requirements: 50 mm above, 20 mm below, 20 mm to the side, and 20 mm forward. Zero clearance needed behind the unit.","metaTitle":"Siemens 3RA2120-4NA27-0FB4 SIRIUS Direct Starter, 28 A AC-3","metaDescription":"Siemens 3RA2120-4NA27-0FB4 SIRIUS direct starter, 28 A AC-3 at 400 V, 690 V max, Class 10, S0 size, 24 V coil. Active production, quoted to order.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Motor Starters"],"specifications":{"Depth":"107 mm","Width":"45 mm","title":"3RA2120-4NA27-0FB4","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 23.0...28.0 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":"7.5 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":"28 A","at AC-3e rated value maximum":"690 V","at AC-3e at 400 V rated value":"28 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":"3RV2021-4NA10","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","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":"364 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":"23 ... 28 A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.aoctrl.com/708d9d68f463ac0aadda11d6077b4eed.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=224542&mlfb=3RA2120-4NA27-0FB4"},"ai":{"faq":[],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RA2120-4NA27-0FB4","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/3RA2120-4NA27-0FB4 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}}