{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RH2122-4LB40","brand":"Siemens","brandSlug":"siemens","productSlug":"3RH2122-4LB40","canonicalUrl":"https://aoctrl.com/siemens/3RH2122-4LB40","factsUrl":"https://aoctrl.com/api/mcp/products/3RH2122-4LB40","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS coupling relay, 3RH2122-4LB40, for switching auxiliary circuits, 24 VDC coil, 2 NO contacts, screw and snap-on mounting on 35 mm DIN rail.","salesMarkdown":"The Siemens SIRIUS 3RH2122-4LB40 is a coupling relay for switching auxiliary circuits, sized for the S00 contactor frame. The coil is rated 24 V DC with a closing and holding power of 2.8 W — a steady-state draw that a standard 24 VDC power supply handles without issue. The built-in varistor surge suppressor means you don't need to add an external flyback diode across the coil; the suppression is already inside the relay package. The contact block provides 2 instantaneous NO contacts. The continuous current rating varies by voltage: at 24 V it carries 10 A, at 230 V it also carries 10 A, but at 400 V it drops to 3 A, and at 690 V to 1 A. For a 24 VDC control circuit, the full 10 A is available; for higher-voltage auxiliary loads, use the voltage-specific derating curve. For DC loads, the switching frequency is given as 7 to 20 ms — this is the contact bounce/arcing window, not a cycles-per-hour figure. Dimensions are 73 mm deep, 45 mm wide, and 57.5 mm high.","metaTitle":"Siemens 3RH2122-4LB40 SIRIUS Coupling Relay, 24 VDC, 10 A","metaDescription":"Siemens SIRIUS 3RH2122-4LB40 coupling relay for switching auxiliary circuits. Rated 24 VDC coil, 10 A at 24 V. Screw and snap-on mounting on 35 mm DIN rail. Active production.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":null,"categoryPath":["Contactors"],"specifications":{"Depth":"73 mm","Width":"45 mm","at AC":"10 000 1/h","at DC":"7 ... 20 ms","title":"3RH2122-4LB40","Height":"57.5 mm","Upwards":"10 mm","Forwards":"10 mm","Downwards":"10 mm","Arcing Time":"10 ... 15 ms","At The Side":"6 mm","Rated Value":"24 V","description":"Coupling contactor relay railway 2 NO + 2 NC, 24 V DC, 0.7... 1.25* US, with varistor integrated, Size S00, ring cable lug connection","Initial Value":"0.7","During Storage":"-55 ... +80 °C","lifecycle_stage":"current","During Operation":"-25 ... +60 °C","Fastening Method":"screw and snap-on mounting onto 35 mm DIN rail","Full-Scale Value":"1.25","Mounting Position":"+/-180° rotation possible on vertical mounting surface; can be tilted forward and backward by +/- 22.5° on vertical mounting surface","Size Of Contactor":"S00","Product Brand Name":"SIRIUS","Degree Of Pollution":"3","Product Designation":"Coupling relay for switching auxiliary circuits","at 24 V rated value":"10 A","at 60 V rated value":"4.7 A","Of Contactor Typical":"30 000 000","at 110 V rated value":"3 A","at 220 V rated value":"1.2 A","at 230 V rated value":"10 A","at 400 V rated value":"3 A","at 440 V rated value":"0.5 A","at 500 V rated value":"2 A","at 600 V rated value":"0.26 A","at 690 V rated value":"1 A","Instantaneous Contact":"2","Relative Humidity Minimum":"10 %","Substance Prohibitance (Date)":"10/01/2009","Design Of The Surge Suppressor":"with varistor","Product Extension Auxiliary Switch":"No","closing power of magnet coil at DC":"2.8 W","holding power of magnet coil at DC":"2.8 W","Surge Voltage Resistance Rated Value":"6 kV","operating frequency at DC-12 maximum":"1 000 1/h","operating frequency at DC-13 maximum":"1 000 1/h","operational current at AC-12 maximum":"10 A","reference code according to IEC 81346-2":"K","Contact Reliability Of Auxiliary Contacts":"1 faulty switching per 100 million (17 V, 1 mA)","with low demand rate according to SN 31920":"40 %","with high demand rate according to SN 31920":"73 %","number of NC contacts for auxiliary contacts":"2","number of NO contacts for auxiliary contacts":"2","Type Of Voltage Of The Control Supply Voltage":"DC","contact rating of auxiliary contacts according to UL":"A600 / Q600","Identification Number And Letter For Switching Elements":"21","Installation Altitude At Height Above Sea Level Maximum":"2 000 m","Of The Contactor With Added Auxiliary Switch Block Typical":"10 000 000","Type Of Electrical Connection For Auxiliary And Control Circuit":"ring terminal lug connection","insulation voltage with degree of pollution 3 at AC rated value":"690 V","Of The Contactor With Added Electronically Optimized Auxiliary Switch Block Typical":"5 000 000","Design Of The Fuse Link For Short-Circuit Protection Of The Auxiliary Switch Required":"fuse gL/gG: 10 A","design of the miniature circuit breaker for short-circuit protection of the auxiliary circuit up to 230 V":"C characteristic: 6 A; 0.4 kA"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.aoctrl.com/8bdffcb9c86a531afcbe516e323744a2.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=222321&mlfb=3RH2122-4LB40"},"ai":{"faq":[{"question":"What are the key ratings for the 3RH2122-4LB40?","answer":"The coil is 24 VDC at 2.8 W. The contacts are 2 NO, rated 10 A at 24 V and 230 V, derating to 3 A at 400 V and 1 A at 690 V. Mechanical life is 30,000,000 cycles. The relay mounts on 35 mm DIN rail and measures 73 x 45 x 57.5 mm."},{"question":"What is the closest functional alternative to the 3RH2122-4LB40?","answer":"The 3RT2016-1BB41-ZW97 is a SIRIUS contactor in the same S00 frame size, but it is a power contactor for motor loads, not a coupling relay for auxiliary circuits. The 3RH2122-4LB40 is the correct part when you need a dedicated auxiliary relay with a 24 VDC coil and 2 NO contacts; the 3RT2016 series is for switching main motor circuits. They share the same DIN-rail footprint and mounting hole pattern, so a panel designed for one can physically accept the other, but the electrical function is different."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RH2122-4LB40","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/3RH2122-4LB40 when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-08-11T15:51:03.652Z","lastPublished":"2026-08-11T15:51:03.652Z","indexable":true}}