{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RH1921-2FA31","brand":"Siemens","brandSlug":"siemens","productSlug":"3RH1921-2FA31","canonicalUrl":"https://aoctrl.com/siemens/3RH1921-2FA31","factsUrl":"https://aoctrl.com/api/mcp/products/3RH1921-2FA31","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS auxiliary switch block, 3 NO + 1 NC, spring-loaded terminals, snap-on mounting for 3RT1 contactor relays and motor contactors, IP20 front, 51 mm depth.","salesMarkdown":"It uses spring-loaded terminals for the auxiliary and control circuit connections, accepting 2x (0.5 to 2.5 mm²) solid or stranded wire without ferrules, or 2x (0.5 to 1.5 mm²) with core-end processing. The block measures 51 mm deep by 44 mm wide by 38 mm high and carries an IP20 protection rating on the front face. ## Lifecycle and replacement This part is a phased-out product. The manufacturer lists the successor as the SIRIUS 3RH2 series auxiliary switch blocks. For new designs or a direct drop-in replacement, evaluate the 3RH2 series — the 3RH2131-2AK60 (3 NO + 1 NC, spring terminals, size S00) is the closest functional peer, though it mounts on size S00 contactors rather than the S0 through S12 range of the original. The AC-15 rated operational current varies by voltage: 10 A at 24 V, 6 A at 125 V, 6 A at 230 V, 6 A at 250 V, 3 A at 400 V, and 1 A at 690 V. These are the inductive-load ratings for solenoid and contactor coils — the most common duty for an auxiliary block. The DC switching ratings follow a different curve: 6 A at 24 V, 4.7 A at 60 V, 3 A at 110 V, 1.2 A at 220 V, 0.5 A at 440 V, and 0.26 A at 600 V. The 10 A maximum applies across the board, but the voltage-specific derating is what governs real-world fit. The spring-loaded terminals accept 2x (0.5 to 2.5 mm²) without ferrules or 2x (0.5 to 1.5 mm²) with ferrules; AWG equivalents are 2x (20 to 14). The 51 mm depth keeps the block within the envelope of the contactor it mounts on, so it does not increase the panel depth beyond the base device.","metaTitle":"Siemens 3RH1921-2FA31 SIRIUS Auxiliary Switch Block, 3NO+1NC","metaDescription":"Siemens SIRIUS 3RH1921-2FA31 auxiliary switch block, 3 NO + 1 NC, spring-loaded terminals, snap-on for 3RT1 contactors. Phased-out; successor 3RH2 series available. Sourced to orde","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":null,"categoryPath":["Contactors"],"specifications":{"Note":"with 3RT1","Depth":"51 mm","Width":"44 mm","Height":"38 mm","Maximum":"10 A","at 24 V":"6 A","at 60 V":"2 A","at 110 V":"1 A","at 125 V":"6 A","at 220 V":"0.3 A","at 230 V":"6 A","at 250 V":"6 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 Brand Name":"SIRIUS","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","at 600 V rated value":"0.26 A","Instantaneous Contact":"3","With Core End Processing":"2x (0.5 ... 1.5 mm²)","Without Core End Processing":"2x (0.5 ... 2.5 mm²)","at AC-15 at 690 V rated value":"1 A","protection class IP on the front":"IP20","Surge Voltage Resistance Rated Value":"6 kV","at AWG cables for auxiliary contacts":"2x (20 ... 14)","Contact Reliability Of Auxiliary Contacts":"1 faulty switching per 100 million (17 V, 1 mA)","Mechanical Service Life (Switching Cycles) Typical":"10 000 000","Type Of Electrical Connection For Auxiliary And Control Circuit":"spring-loaded terminals","insulation voltage with degree of pollution 3 at AC rated value":"690 V"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"priceTiers":null},"links":{"datasheetUrl":null,"sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=121066&mlfb=3RH1921-2FA31","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RH1921-2FA31/alternatives.json"},"ai":{"faq":[{"question":"Where can I buy 3RH1921-2FA31 and get a price?","answer":"The 3RH1921-2FA31 is sourced and quoted to order against an RFQ through independent distribution. Availability and current pricing are confirmed at quote time — submit an RFQ for a firm price and lead time."},{"question":"What is the closest functional second-source for 3RH1921-2FA31?","answer":"The closest functional peer is the SIRIUS 3RH2131-2AK60, which also offers 3 NO + 1 NC contacts with spring-loaded terminals. The key difference is mounting size: the 3RH1921-2FA31 fits contactors in sizes S0 through S12, while the 3RH2131-2AK60 is sized for S00 contactors. Verify the base contactor frame size before substituting."},{"question":"What does the note 'with 3RT1' mean for this part?","answer":"The note indicates the 3RH1921-2FA31 auxiliary switch block is designed to mount directly onto 3RT1 series contactor relays and power contactors. It snaps onto the front of the contactor without additional hardware."},{"question":"What is the depth of 3RH1921-2FA31?","answer":"The depth is 51 mm. Width is 44 mm and height is 38 mm. These dimensions keep the auxiliary block within the contactor footprint when mounted."},{"question":"Will 3RH1921-2FA31 drop into a panel specified around 3RH2131-2AK60 without rewiring?","answer":"Not directly. Both use spring-loaded terminals and the same contact arrangement (3 NO + 1 NC), but the 3RH1921-2FA31 mounts on contactors in sizes S0 through S12, while the 3RH2131-2AK60 is sized for S00 contactors. If the base contactor frame is S00, the 3RH1921-2FA31 will not snap on. Wiring is compatible if the terminal function mapping matches, but the mechanical fit must be verified first."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RH1921-2FA31","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/3RH1921-2FA31 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}}