{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RT1945-5AC21","brand":"Siemens","brandSlug":"siemens","productSlug":"3RT1945-5AC21","canonicalUrl":"https://aoctrl.com/siemens/3RT1945-5AC21","factsUrl":"https://aoctrl.com/api/mcp/products/3RT1945-5AC21","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RT1945-5AC21 magnet coil, Size S3, 24 V AC 50/60 Hz, screw terminal.","salesMarkdown":"The Siemens SIRIUS 3RT1945-5AC21 is a magnet coil for Size S3 contactors, wound for 24 V AC at 50/60 Hz and terminated with a screw terminal block. This is a phased-out product; the manufacturer has designated the SIRIUS 3RT2 series as the official successor. Rated for 24 V AC control voltage at both 50 and 60 Hz, so it drops into any existing Size S3 contactor frame that expects that coil voltage — no rewiring of the control transformer needed. The screw terminal matches legacy panel wiring practices; no crimp tool required for the coil connection. Because it is a Size S3 coil, it physically fits only the S3 contactor frame (the 3RT104/3RT105 class). It will not mechanically seat in a Size S0 or S00 contactor — the magnet yoke and armature dimensions are different.","metaTitle":"Siemens 3RT1945-5AC21 SIRIUS Magnet Coil, 24 V AC, Size S3","metaDescription":"Siemens SIRIUS 3RT1945-5AC21 magnet coil for Size S3 contactors. 24 V AC 50/60 Hz, screw terminal. Phased-out; successor is SIRIUS 3RT2. Sourced to order.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":null,"categoryPath":["Contactors"],"specifications":{"lifecycle_stage":"current","Product Brand Name":"SIRIUS","Product Designation":"Magnet coil"}},"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=474750&mlfb=3RT1945-5AC21","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RT1945-5AC21/alternatives.json"},"ai":{"faq":[{"question":"What replaces this part?","answer":"The manufacturer lists the SIRIUS 3RT2 series as the official successor. This is a different product generation; verify the mounting footprint and control voltage of the 3RT2 coil before ordering."},{"question":"What is the control voltage and frequency?","answer":"Rated for 24 V AC at both 50 and 60 Hz, with a screw terminal connection."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RT1945-5AC21","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/3RT1945-5AC21 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}}