{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RA2125-4NH27-0FB4","brand":"Siemens","brandSlug":"siemens","productSlug":"3RA2125-4NH27-0FB4","canonicalUrl":"https://aoctrl.com/siemens/3RA2125-4NH27-0FB4","factsUrl":"https://aoctrl.com/api/mcp/products/3RA2125-4NH27-0FB4","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RA2125-4NH27-0FB4 direct-on-line starter, size S0, 15 kW at 400 V AC-3, CLASS 10 thermal overload, spring-loaded terminals, for 60 mm busbar systems.","salesMarkdown":"## What this SIRIUS direct starter is The Siemens 3RA2125-4NH27-0FB4 is a SIRIUS direct-on-line starter — a fully assembled combination motor starter that integrates a contactor, a thermal overload relay, and a circuit-breaker in one package, sized S0. The thermal (bimetallic) overload release is set to CLASS 10 trip characteristics, which means it protects standard squirrel-cage motors during start-up without nuisance tripping on normal acceleration. A magnetic short-circuit trip handles the fault side — the supplied circuit-breaker is a 3RV2021-4NA25, coordinated with the contactor for Type 2 coordination per IEC 60947-4-1. ## Mounting and integration — built for 60 mm busbars This starter is designed specifically for snapping onto 60 mm busbar systems — not for DIN rail. The supplied busbar adapter (8US1251-5NT11) locks it onto the busbar, so plan the panel layout around vertical busbar mounting, not a standard top-hat rail. Mounting position is vertical only. The physical footprint: 45 mm wide, 260 mm tall, 165 mm deep — the width is tight for a size S0, but the depth pushes into the enclosure, so allow clearance behind the panel. Clearance distances are specified: 50 mm upwards, 20 mm forwards, 20 mm at the sides, 10 mm downwards, and 0 mm backwards — the back is flush against the busbar, no extra space needed behind. Both the main power circuit and the auxiliary/control circuit terminate with spring-loaded terminals — push-in style for solid or ferruled stranded wire. No screw torque to check; just strip, push, and pull-test. The auxiliary switch extension is supported. ## Supplied components — what's in the box The 3RA2125-4NH27-0FB4 ships as a pre-assembled unit containing a 3RT2027-2FB40 contactor, a 3RV2021-4NA25 circuit-breaker, a 3RA2921-2AA00 link module, and the 8US1251-5NT11 busbar adapter — all matched for coordination. Operating ambient temperature range is -20 to +60 °C with a relative humidity of 10 to 95 % during operation — suitable for most indoor industrial environments without condensation control.","metaTitle":"Siemens 3RA2125-4NH27-0FB4 SIRIUS Direct Starter","metaDescription":"Siemens 3RA2125-4NH27-0FB4 SIRIUS direct-on-line starter, 15 kW at 400 V AC-3, size S0, CLASS 10 thermal overload, spring terminals, for 60 mm busbars.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Motor Starters"],"specifications":{"Depth":"165 mm","Width":"45 mm","title":"3RA2125-4NH27-0FB4","Height":"260 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...28 A 24 V DC Spring-type terminal for 60 mm busbar systems (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":"for snapping onto 60 mm busbar systems","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 400 V rated value":"15 000 W","Design Of The Product":"for 60 mm busbars","For Main Current Circuit":"spring-loaded terminals","Temperature Compensation":"-20 ... +60 °C","Of The Supplied Contactor":"3RT2027-2FB40","Of The Supplied Link Module":"3RA2921-2AA00","Size Of The Circuit-Breaker":"S0","at AC-3 rated value maximum":"690 V","Design Of The Overload Release":"thermal (bimetallic)","Of The Supplied Busbar Adapter":"8US1251-5NT11","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":"3RV2021-4NA25","degree of protection NEMA rating":"other","For Auxiliary And Control Circuit":"spring-loaded terminals","Product Extension Auxiliary Switch":"Yes","Relative Humidity During Operation":"10 ... 95 %","Surge Voltage Resistance Rated Value":"6 kV","Number Of Poles For Main Current Circuit":"3","Product Function Short Circuit Protection":"Yes","protocol is supported AS-Interface protocol":"No","number of NC contacts for auxiliary contacts":"1","number of NO contacts for auxiliary contacts":"1","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","operational current at AC-3 at 400 V rated value":"28 A","Mechanical Service Life (Switching Cycles) Of Contactor Typical":"10 000 000","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/178c382c6f10386d5d589f1718c8bc0e.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=552564&mlfb=3RA2125-4NH27-0FB4"},"ai":{"faq":[{"question":"What is the 3RA2125-4NH27-0FB4 rated for at 400 V?","answer":"The trip class is CLASS 10 for standard motor starting."},{"question":"Does the 3RA2125-4NH27-0FB4 mount on DIN rail or busbars?","answer":"It snaps onto 60 mm busbar systems using the supplied busbar adapter — not on standard DIN rail. Mounting position is vertical only."},{"question":"What terminal type does this starter use?","answer":"Spring-loaded terminals (push-in) on both the main power circuit and the auxiliary/control circuit. No screw torque required; suitable for solid or ferruled stranded wire."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RA2125-4NH27-0FB4","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/3RA2125-4NH27-0FB4 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}}