{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RU2126-4FB1","brand":"Siemens","brandSlug":"siemens","productSlug":"3RU2126-4FB1","canonicalUrl":"https://aoctrl.com/siemens/3RU2126-4FB1","factsUrl":"https://aoctrl.com/api/mcp/products/3RU2126-4FB1","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RU2126-4FB1, size S0 thermal overload relay, Class 10, 18.5 kW at 400 V, screw-type terminals, active production.","salesMarkdown":"The relay is rated for 18.5 kW at 400 V, and can handle up to 690 V rated insulation voltage. It uses screw-type terminals for the main current circuit, sized for M4 screws, and accepts 2x (0.5 to 1.5 mm²) or 2x (0.75 to 2.5 mm²) solid or stranded wire. The auxiliary switch is integrated, with a note for message \"Tripped\" — that's the NC contact that changes state when the bimetals warp, giving you a remote trip indication. Class 10 is the key selection parameter here. It's designed to coordinate with contactors and circuit breakers in a motor starter assembly — the overload relay handles the thermal protection, not the short-circuit interruption. The 18.5 kW rating at 400 V is for AC-3e duty (squirrel-cage motors: starting, switching off during running). At 480 V it's rated for 40 A, and at 690 V for 37 kW. The temperature compensation range of -40 to +60 °C means the bimetal curve stays accurate even if the panel ambient drifts — critical when the relay sits next to a hot contactor. That means you need to plan for DIN rail or direct panel mounting, and wire it separately from the contactor. The size S0 frame is compact: 45 mm wide, 97 mm high, 95 mm deep. For the auxiliary contacts, the screw terminals use a Pozidriv PZ 2 tip, with a screwdriver shaft diameter of 5 to 6 mm. The MTTF with high demand rate is listed at 2,280 years — a reliability figure for safety-related applications, though this is a standard thermal relay, not a safety-rated device.","metaTitle":"Siemens 3RU2126-4FB1 SIRIUS Thermal Overload Relay, Class 10","metaDescription":"Siemens SIRIUS 3RU2126-4FB1 thermal overload relay, size S0, Class 10 trip, 18.5 kW at 400 V. Active production. Screw terminals. RFQ for current lead time.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Overload Relays"],"specifications":{"Note":"for message \"Tripped\"","Depth":"95 mm","Width":"45 mm","Height":"97 mm","at 24 V":"2 A","at 60 V":"0.3 A","Per Pole":"3.2 W","at 110 V":"0.22 A","at 120 V":"3 A","at 125 V":"0.22 A","at 220 V":"0.11 A","at 230 V":"2 A","at 400 V":"1 A","Trip Class":"CLASS 10","Rated Value":"690 V","During Storage":"-55 ... +80 °C","lifecycle_stage":"current","During Operation":"-40 ... +70 °C","During Transport":"-55 ... +80 °C","Fastening Method":"stand-alone installation","For Main Contacts":"M4","Mounting Position":"any","Solid Or Stranded":"2x (0.5 ... 1.5 mm²), 2x (0.75 ... 2.5 mm²)","Product Brand Name":"SIRIUS","Product Designation":"thermal overload relay","at 400 V rated value":"18.5 kW","at 480 V rated value":"40 A","at 500 V rated value":"22 kW","at 600 V rated value":"40 A","at 690 V rated value":"37 kW","Size Of Overload Relay":"S0","For Main Current Circuit":"screw-type terminals","Temperature Compensation":"-40 ... +60 °C","MTTF with high demand rate":"2 280 y","Design Of Screwdriver Shaft":"Diameter 5 ... 6 mm","Size Of The Screwdriver Tip":"Pozidriv PZ 2","at AC-3e rated value maximum":"690 V","Substance Prohibitance (Date)":"10/01/2009","Design Of The Auxiliary Switch":"integrated","Design Of The Overload Release":"thermal","Operating Frequency Rated Value":"50 ... 60 Hz","Operational Current Rated Value":"40 A","at AWG cables for main contacts":"2x (16 ... 12), 2x (14 ... 8)","For Auxiliary And Control Circuit":"screw-type terminals","Between Main And Auxiliary Circuit":"440 V","Relative Humidity During Operation":"10 ... 95 %","Display Version For Switching Status":"Slide switch","Surge Voltage Resistance Rated Value":"6 kV","at AWG cables for auxiliary contacts":"2x (20 ... 16), 2x (18 ... 14)","Of The Auxiliary And Control Contacts":"M3","Between Auxiliary And Auxiliary Circuit":"440 V","reference code according to IEC 81346-2":"F","Finely Stranded With Core End Processing":"2x (0.5 ... 1.5 mm²), 2x (0.75 ... 2.5 mm²)","Number Of Poles For Main Current Circuit":"3","For Main Contacts With Screw-Type Terminals":"2 ... 2.5 N·m","number of CO contacts for auxiliary contacts":"0","number of NC contacts for auxiliary contacts":"1","number of NO contacts for auxiliary contacts":"1","shock resistance according to IEC 60068-2-27":"8g / 11 ms","For Auxiliary Contacts With Screw-Type Terminals":"0.8 ... 1.2 N·m","operational current at AC-3e at 400 V rated value":"40 A","Size Of Contactor Can Be Combined Company-Specific":"S0","contact rating of auxiliary contacts according to UL":"B600 / R300","Installation Altitude At Height Above Sea Level Maximum":"2 000 m","Arrangement Of Electrical Connectors For Main Current Circuit":"Top and bottom","For Short-Circuit Protection Of The Auxiliary Switch Required":"fuse gG: 6 A, quick: 10 A","insulation voltage with degree of pollution 3 at AC rated value":"690 V","Product Component Removable Terminal For Auxiliary And Control Circuit":"No","power loss [W] for rated value of the current at AC in hot operating state":"9.6 W","Adjustable Current Response Value Current Of The Current-Dependent Overload Release":"34 ... 40 A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":null,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.aoctrl.com/87c1f40ff2ceb030b6ca66b6af2ff7dc.pdf","sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=324585&mlfb=3RU2126-4FB1","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RU2126-4FB1/alternatives.json"},"ai":{"faq":[{"question":"What is the closest functional alternative to the 3RU2126-4FB1?","answer":"The 3RV1011-1HA10 is a different device class — it's a motor circuit breaker (combined short-circuit and overload protection), not a standalone thermal overload relay. The 3RU2126-4FB1 is a thermal overload relay designed to pair with a contactor (like the 3RT2 series). They are not drop-in replacements; the 3RV combines functions the 3RU does not. For a direct functional equivalent in the same SIRIUS family, look at other 3RU2 size S0 relays with the same trip class and current range."},{"question":"What does the note \"for message 'Tripped'\" mean on the 3RU2126-4FB1?","answer":"It refers to the integrated auxiliary switch contact that changes state when the thermal overload relay trips. That contact provides a remote signal (a 'tripped' message) to a PLC or indicator light, so you know the relay has operated without having to visually inspect it."},{"question":"What are the key dimensions of the 3RU2126-4FB1?","answer":"The size S0 relay measures 45 mm wide, 97 mm high, and 95 mm deep. It's designed for stand-alone installation, not direct snap-on mounting to a contactor."},{"question":"What compliance documentation is available for the 3RU2126-4FB1?","answer":"The substance prohibition date is 10/01/2009, indicating RoHS compliance from that date. As a Siemens SIRIUS product, it carries CE marking for the European market and is designed to meet relevant IEC standards for thermal overload relays. Specific UL/CSA file numbers are not listed in this data set."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RU2126-4FB1","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/3RU2126-4FB1 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}}