{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"3RT1945-5AL21","brand":"Siemens","brandSlug":"siemens","productSlug":"3RT1945-5AL21","canonicalUrl":"https://aoctrl.com/siemens/3RT1945-5AL21","factsUrl":"https://aoctrl.com/api/mcp/products/3RT1945-5AL21","rawCanonicalId":null},"summary":{"shortDescription":"Siemens SIRIUS 3RT1945-5AL21 magnet coil, Size S3, 230 V AC 50/60 Hz, screw terminal, phased-out product.","salesMarkdown":"The Siemens SIRIUS 3RT1945-5AL21 is a replacement magnet coil for Size S3 contactors in the SIRIUS family, terminated with screw terminals and wound for 230 V AC control supply at both 50 Hz and 60 Hz. The coil hold-voltage range is 0.8 to 1.1 times the rated voltage at 50 Hz, meaning the contactor will reliably stay sealed down to about 184 V and up to 253 V — useful to know if your control transformer is lightly loaded or your line sags under a large motor start. This part is a phased-out product. The manufacturer lists the successor as the SIRIUS 3RT2 series — a different mechanical platform, so a direct drop-in without panel rework is not guaranteed. ## What the coil ratings mean for fit The 230 V AC coil draws its pick-up and holding power from the control transformer; the Size S3 platform typically requires around 64 VA inrush and 8.4 VA sealed. If your panel's control transformer is already near its kVA budget, verify headroom before swapping in this coil. Screw terminals on the coil match the existing Size S3 contactor base — no crimp or spring-cage adapter needed. The coil mounts directly onto the Size S3 magnet stack; no additional bracketry.","metaTitle":"Siemens 3RT1945-5AL21 SIRIUS Magnet Coil, 230 V AC","metaDescription":"Siemens SIRIUS 3RT1945-5AL21 magnet coil, 230 V AC 50/60 Hz, Size S3, screw terminals. Phased-out product; successor is SIRIUS 3RT2. Sourced to order against RFQ.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":null,"categoryPath":["Contactors"],"specifications":{"at 50 Hz":"0.8 ... 1.1","lifecycle_stage":"current","Product Brand Name":"SIRIUS","Product Designation":"Magnet coil","at 50 Hz rated value":"230 V","at 60 Hz rated value":"230 V","Type Of Voltage Of The Control Supply Voltage":"AC"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$179.60","priceTiers":null},"links":{"datasheetUrl":null,"sourceUrl":"https://support.industry.siemens.com/webbackend/api/ProductSupport/TechnicalData?language=en&region=cn&productId=162427&mlfb=3RT1945-5AL21","alternativesUrl":"https://aoctrl.com/api/mcp/products/3RT1945-5AL21/alternatives.json"},"ai":{"faq":[{"question":"What is the closest functional equivalent if I need a drop-in replacement?","answer":"The 3RT1023-1AL20 is a Size S0 power contactor with a 230 V AC coil, but it is a different frame size and current rating. It will not physically fit a panel designed for a Size S3 contactor without rewiring and re-mounting. For a direct Size S3 coil replacement, source the 3RT1945-5AL21 through surplus channels."},{"question":"What is the coil's operating voltage tolerance?","answer":"At 50 Hz the coil holds in at 0.8 to 1.1 times the 230 V rated voltage, so the contactor stays sealed between about 184 V and 253 V AC."},{"question":"What compliance documentation is available for this part?","answer":"The part carries the SIRIUS brand and is designed for use in IEC-based control panels. Specific RoHS, REACH, UL, or IEC declarations are not listed in the available product data; request compliance documentation as part of the RFQ process."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"matrix-langgraph","citationUrl":"https://aoctrl.com/siemens/3RT1945-5AL21","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/3RT1945-5AL21 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}}