{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RH1921-1KA20","brand":"Siemens","brandSlug":"siemens","productSlug":"3RH1921-1KA20","canonicalUrl":"https://aoctrl.com/siemens/3RH1921-1KA20","factsUrl":"https://aoctrl.com/api/mcp/products/3RH1921-1KA20","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS auxiliary switch, 2 N/O instantaneous contacts, screw terminals, snap-on for S0 contactors, 10 A AC-12, 6 kV surge, 71 mm depth.","salesMarkdown":"It snaps onto the contactor relay or power contactor and adds two instantaneous N/O contacts for status feedback, interlocking, or control logic. The screw-type terminals accept 2x (0.5...1.5 mm²) solid or stranded, or 2x (0.75...2.5 mm²) — the same wiring practice as the base contactor, so no change in ferrule or strip length on the line. Rated operational current hits 10 A at AC-12 (resistive) for 24 V and 230 V circuits, and 6 A at 24 V for general-use switching. At 400 V it still handles 3 A, which covers most control transformer secondaries and pilot-duty loads in a 400 V panel. Surge voltage withstand is 6 kV — enough for IEC 60947-1 impulse coordination in an industrial enclosure. The contacts are mirror contacts per IEC 60947-4-1 when used with the 3RT1 contactor series, meaning the N/O and N/C positions are mechanically linked so you can rely on the feedback for safety circuits. Snap-on mounting to the S0 contactor — no tools, no DIN rail adapter. The block is 10 mm wide, 80 mm high, 71 mm deep. That 71 mm depth is the critical dimension when the contactor is already against the back panel or a busbar shroud; it matches the S0 contactor body depth, so the assembly stays within the same envelope. IP20 on the front face keeps fingers out of live terminals but expects enclosure protection for washdown or dust. ## Switching capacity by voltage — the so-what The 3RH1921-1KA20 carries two separate current ratings: one set for general-use switching (the 'at X V' values in the spec table) and a second set for AC-12 duty. The general-use ratings are: 6 A at 24 V, 2 A at 48 V and 60 V, 1 A at 110 V, 0.9 A at 125 V, 0.3 A at 220 V and 250 V, and 3 A at 400 V. The AC-12 ratings are higher: 10 A at 24 V, 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, and 0.5 A at 440 V. The AC-12 curve is the one to use for resistive loads like contactor coils, solenoid valves, and indicator lamps; the general-use curve governs inductive or mixed loads. If your control circuit is 24 V DC and you are switching a DC coil, use the DC ratings — the AC-12 numbers do not apply.","metaTitle":"Siemens SIRIUS 3RH1921-1KA20 Auxiliary Switch, 2 N/O, 10 A,","metaDescription":"Siemens SIRIUS 3RH1921-1KA20 auxiliary switch for S0 contactors. 2 N/O contacts, 10 A AC-12, 6 kV surge. Snap-on mount. Active production, sourced to order. Request quote.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Contactors"],"specifications":{"Depth":"71 mm","Width":"10 mm","Height":"80 mm","at 24 V":"6 A","at 48 V":"2 A","at 60 V":"2 A","at 110 V":"1 A","at 125 V":"0.9 A","at 220 V":"0.3 A","at 230 V":"6 A","at 250 V":"0.3 A","at 400 V":"3 A","During Storage":"-55 ... +80 °C","lifecycle_stage":"current","During Operation":"-25 ... +60 °C","Fastening Method":"snap-on mounting","Product Category":"Auxiliary switch","Size Of Contactor":"S0","Solid Or Stranded":"2x (0.5 ... 1.5 mm²), 2x (0.75 ... 2.5 mm²)","Product Brand Name":"SIRIUS","Product Designation":"auxiliary switch","Suitability For Use":"Contactor relay and power contactor","at 24 V rated value":"10 A","at 60 V rated value":"4.7 A","at 110 V rated value":"3 A","at 220 V rated value":"1.2 A","at 440 V rated value":"0.5 A","Design Of The Product":"second can be mounted laterally","Instantaneous Contact":"2","Substance Prohibitance (Date)":"07/01/2006","protection class IP on the front":"IP20","Surge Voltage Resistance Rated Value":"6 kV","at AWG cables for auxiliary contacts":"2x (20 ... 16), 2x (18 ... 14)","Finely Stranded With Core End Processing":"2x (0.5 ... 1.5 mm²), 2x (0.75 ... 2.5 mm²)","Contact Reliability Of Auxiliary Contacts":"1 faulty switching per 100 million (17 V, 1 mA)","mirror contact according to IEC 60947-4-1":"Yes; with 3RT1","Mechanical Service Life (Operating Cycles) Typical":"10 000 000","operational current of auxiliary contacts at AC-12 maximum":"10 A","Type Of Electrical Connection For Auxiliary And Control Circuit":"screw-type terminals","insulation voltage with degree of pollution 3 at AC rated value":"500 V","number of CO contacts of auxiliary contacts instantaneous contact":"0","AWG number as coded connectable conductor cross section for auxiliary contacts":"20 ... 14"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.aoctrl.com/87f3a39279259e93c13051c13d3ecde8.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=407341&mlfb=3RH1921-1KA20","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RH1921-1KA20/alternatives.json"},"ai":{"faq":[{"question":"Who supplies 3RH1921-1KA20 and how is it quoted for volume purchases?","answer":"This part is sourced through independent industrial-automation distribution. Volume pricing and lead time are confirmed at quote time against a formal RFQ. Submit a request with your quantity and target delivery window for a firm quote."},{"question":"When sourcing 3RH1921-1KA20, what's the closest functional second-source — 3RH2122-1BA40?","answer":"The 3RH2122-1BA40 is a different variant — it carries two N/O plus two N/C contacts and is physically wider (45 mm) for the S2/S3 contactor frame. It will not drop into an S0 panel without rewiring and a larger enclosure. The 3RH1921-1KA20 is the correct S0 auxiliary block for a 2 N/O configuration."},{"question":"What is 3RH1921-1KA20's listed depth (71 mm) on this component line?","answer":"The depth is 71 mm, matching the S0 contactor body depth so the auxiliary block does not protrude beyond the contactor envelope. This is the dimension to check against back-panel clearance or busbar shrouds."},{"question":"What is 3RH1921-1KA20's listed width (10 mm) on this component line?","answer":"The width is 10 mm — one auxiliary block adds 10 mm to the contactor assembly width. Two blocks can be mounted laterally (one on each side) for a total width increase of 20 mm."},{"question":"What compliance documentation does this brand provide for 3RH1921-1KA20 (RoHS, REACH, UL, IEC)?","answer":"The part carries a substance prohibition date of 07/01/2006 (RoHS compliance). It is designed to IEC 60947-4-1 for mirror contact functionality. Insulation voltage is 500 V at pollution degree 3. Specific UL/CSA file numbers and REACH declarations are available on request with the RFQ."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RH1921-1KA20","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/3RH1921-1KA20 when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-09-02T08:15:54.622Z","lastPublished":"2026-09-02T08:15:54.622Z","indexable":true}}