{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.250MRSN","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.250MRSN","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.250MRSN","factsUrl":"https://icboms.com/api/mcp/products/0451.250MRSN","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse NANO²® 451 Series, Board Mount Surface Mount Fuse, 0451.250MRSN, 250 mA, 125 VAC, 50 A Breaking Capacity, Fast Blow, 2-SMD Square End Block, Tape & Reel.","salesMarkdown":"## Active protection for 125 VAC secondary circuits The Littelfuse 0451.250MRSN is an active-production NANO²® 451 series SMD fuse rated for 250 mA continuous current at 125 VAC, with a DC cold resistance of 0.5765 Ohms and a fast-blow response characteristic. Its 50 A breaking capacity at the rated voltage means it safely interrupts a fault current up to that level without rupturing the package — a critical spec for secondary-side protection in power supplies where the prospective short-circuit current can exceed the fuse's interrupt rating if undersized. ## 0.0158 I²t coordinates with downstream traces and FETs The melting I²t of 0.0158 A²s tells you the energy needed to clear the fuse element — this number drives the coordination study with the PCB trace width and the silicon die area of any downstream MOSFET or diode that must survive a fault before the fuse opens. ## 2-SMD square end block for pick-and-place Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, the 0451.250MRSN uses the standard NANO² footprint that mates with common Littelfuse pad layouts — no custom land pattern needed. Supplied on Tape & Reel (TR), it feeds directly into a high-speed pick-and-place machine without a reel-change interruption for most reel capacities. ## CSA and UR approvals cover North American panel builds CSA and UR approval agency markings are listed — the fuse carries the recognized component mark for UL 248-14 and the corresponding CSA standard, so it passes the acceptance gate for most North American industrial and commercial power supplies without a separate agency review.","metaTitle":"Littelfuse 0451.250MRSN NANO² 451 Fuse, 250 mA, 125 VAC","metaDescription":"Littelfuse 0451.250MRSN NANO² 451 SMD fuse, 250 mA, 125 VAC, 50 A breaking capacity. Active lifecycle. CSA, UR approved. Quoted to order.","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)","Fuse Type":"Board Mount (Cartridge Style Excluded)","Melting I²t":"0.0158","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":"0.5765 Ohms","Voltage Rating - AC":"125 V","Current Rating (Amps)":"250 mA","Operating Temperature":"-55°C ~ 125°C","Breaking Capacity @ Rated Voltage":"50A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$1.4614","priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/604a0e4c498aa97d2607992508357d04.pdf","sourceUrl":null,"alternativesUrl":"https://icboms.com/api/mcp/products/0451.250MRSN/alternatives.json"},"ai":{"faq":[{"question":"What is the breaking capacity of 0451.250MRSN?","answer":"The breaking capacity is 50 A at the rated 125 VAC. This is the maximum fault current the fuse can safely interrupt at that voltage without casing rupture or arc continuation."},{"question":"What approvals does the 0451.250MRSN carry?","answer":"The fuse is approved by CSA and UR (UL Recognized), covering the primary North American safety standards for component-level fuses."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.250MRSN","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.250MRSN 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}}