{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.125MRSN","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.125MRSN","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.125MRSN","factsUrl":"https://icboms.com/api/mcp/products/0451.125MRSN","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse Inc. NANO²® 451 series, Board Mount (Cartridge Style Excluded) fuse, 125 mA, 125 VAC, Fast Blow, 50 A breaking capacity, 2-SMD square end block, Surface Mount.","salesMarkdown":"## NANO² 451 — 125 mA fast-blow in a 2-SMD square end block The 0451.125MRSN is a Littelfuse NANO²® 451 series surface-mount fuse, rated 125 mA at 125 VAC with a fast-blow response time. The 50 A breaking capacity at rated voltage means it safely interrupts a short-circuit fault up to that level without rupturing the package — important for secondary-side protection in a power supply where the upstream transformer can deliver that fault current. ## Melting I²t and cold resistance — the coordination numbers Melting I²t is 0.00286 A²s — the energy required to clear the fuse element. This figure drives coordination with downstream components: a capacitor bank with 0.002 A²s inrush stays below the fuse's melting threshold, so the fuse holds during startup. DC cold resistance is 1.7 Ohms, which at 125 mA produces a voltage drop of about 213 mV — negligible in a 125 V circuit but worth checking if the load is a low-voltage rail. ## Temperature range and agency marks CSA and UR approval marks mean the fuse is accepted for North American safety-agency inspections without additional component-level testing. ## Package and lifecycle — active, surface-mount, reel-ready The 2-SMD square end block measures 6.10 x 2.69 x 2.69 mm, fitting standard pick-and-place nozzles. Available in Tape & Reel for production or Cut Tape for prototypes. Sourced to order against the BOM; availability confirmed at RFQ.","metaTitle":"Littelfuse 0451.125MRSN NANO² 451 Fuse, 125 mA, 125 VAC","metaDescription":"Littelfuse 0451.125MRSN NANO² 451 surface-mount fast-blow fuse, 125 mA, 125 VAC, 50 A breaking capacity. Active lifecycle, sourced to order. CSA, UR approved.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Active","categoryPath":["Circuit Protection"],"specifications":{"Mfr":"Littelfuse Inc.","Color":"-","Series":"NANO²® 451","Package":"Tape & Reel (TR) Cut Tape (CT)","Fuse Type":"Board Mount (Cartridge Style Excluded)","Melting I²t":"0.00286","Mounting Type":"Surface Mount","Response Time":"Fast Blow","Package / Case":"2-SMD, Square End Block","Product Status":"Active","Approval Agency":"CSA, UR","lifecycle_stage":"unknown","Size / Dimension":"0.240\\\" L x 0.106\\\" W x 0.106\\\" H (6.10mm x 2.69mm x 2.69mm)","DC Cold Resistance":"1.7 Ohms","Voltage Rating - AC":"125 V","Current Rating (Amps)":"125 mA","Operating Temperature":"-55°C ~ 125°C","Breaking Capacity @ Rated Voltage":"50A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$2.9400","priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/604a0e4c498aa97d2607992508357d04.pdf","sourceUrl":null,"alternativesUrl":"https://icboms.com/api/mcp/products/0451.125MRSN/alternatives.json"},"ai":{"faq":[{"question":"What is the breaking capacity of the 0451.125MRSN at 125 VAC?","answer":"The breaking capacity at rated voltage is 50 A. This means the fuse can safely interrupt a fault current up to 50 A at 125 VAC without external arc-quenching measures."},{"question":"What compliance documentation does Littelfuse provide for 0451.125MRSN?","answer":"The fuse carries CSA and UR approval marks, indicating it meets the safety standards of the Canadian Standards Association and Underwriters Laboratories for North American acceptance. RoHS and REACH compliance documentation is typically available from the manufacturer or distributor upon request."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.125MRSN","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.125MRSN when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-08-11T15:49:49.435Z","lastPublished":"2026-08-11T15:49:49.435Z","indexable":true}}