{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RH1921-1EA20","brand":"Siemens","brandSlug":"siemens","productSlug":"3RH1921-1EA20","canonicalUrl":"https://aoctrl.com/siemens/3RH1921-1EA20","factsUrl":"https://aoctrl.com/api/mcp/products/3RH1921-1EA20","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS auxiliary switch, 3RH1921-1EA20, 2 N/O contacts, screw-type terminals, snap-on mounting for S0 contactor size, 10 A rated.","salesMarkdown":"## What this auxiliary switch does in the panel It's the part you add when the main contactor needs to report its position back to the PLC, interlock a second device, or drive a panel light. The screw-type terminals accept 2x (0.5...1.5 mm²) solid or 2x (0.75...2.5 mm²) stranded, and the 10 mm width means it won't eat up DIN rail space the way a separate relay would. Rated at 10 A for AC-12 duty, the contacts handle typical control-circuit loads — PLC inputs, contactor coils, indicator lamps — without derating down to 24 V. The mirror contact feature per IEC 60947-4-1 (verified with 3RT1 contactors) means the N/O contacts cannot weld closed if the main contacts weld, a requirement for safety circuits that monitor contactor state. ## Current ratings across the voltage range The switching capacity varies significantly with applied voltage, which matters when you're mixing control voltages in the same panel. At 24 V the contacts are rated 6 A (with a 10 A rated value for the contact block itself), at 48 V and 60 V it drops to 2 A, at 110 V it's 1 A, at 230 V it's back to 6 A, and at 400 V it handles 3 A. The 230 V figure covers common single-phase control circuits in European panels; the 400 V rating covers line-voltage pilot devices in three-phase motor starters. ## Mounting and integration with S0 contactors Snap-on mounting directly to the contactor — no DIN rail required, no extra brackets. The 71 mm depth and 80 mm height match the S0 contactor envelope, so the assembly stays within the same panel footprint. Designed as a first laterally mountable block, it can sit on either side of the contactor, which helps when you need to stack multiple auxiliary blocks or a pneumatic timer alongside it. RoHS compliance date is listed as July 1, 2006, covering the original EU directive. The part carries no explicit UL or CSA mark in the evidence, so verify with the factory if your site requires a listed component for the panel certification.","metaTitle":"Siemens 3RH1921-1EA20 SIRIUS Auxiliary Switch, 2 N/O, 10 A,","metaDescription":"Siemens 3RH1921-1EA20 SIRIUS auxiliary switch, 2 N/O contacts, 10 A rated, snap-on for S0 contactors. IP20, screw terminals, mirror contact per IEC 60947-4-1. Available to order.","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":"first laterally mountable","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/de6366c9935af4adfe67b1e7d95adb82.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=18963&mlfb=3RH1921-1EA20","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RH1921-1EA20/alternatives.json"},"ai":{"faq":[{"question":"Will the 3RH1921-1EA20 drop into a panel specified around the 3RH2122-1BA40 without rewiring?","answer":"Both are SIRIUS auxiliary switches for S0 contactors with the same snap-on mounting and screw terminals, so the physical fit is identical. The 3RH1921-1EA20 carries two N/O contacts; the 3RH2122-1BA40 carries a different contact arrangement, so verify your control logic before swapping."},{"question":"What compliance documentation does Siemens provide for the 3RH1921-1EA20?","answer":"RoHS compliance is documented with a substance prohibition date of July 1, 2006. The mirror contact design is certified per IEC 60947-4-1 when used with 3RT1 contactors."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RH1921-1EA20","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/3RH1921-1EA20 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}}