{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.400NR","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.400NR","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.400NR","factsUrl":"https://icboms.com/api/mcp/products/0451.400NR","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse Inc. NANO²® 451 series, 0451.400NR, surface-mount fast-blow fuse, 400 mA, 125 V AC/DC, 50 A breaking capacity, 2-SMD square end block, CSA, cULus.","salesMarkdown":"## Obsolete — the BOM decision driver Littelfuse has marked the 0451.400NR as Obsolete. For existing designs, procurement must source through independent or surplus distribution channels — the part is not available through the factory's standard ordering process. The 0451.400NR is a 400 mA fast-blow fuse from the NANO² 451 series, rated 125 V AC and 125 V DC with a 50 A breaking capacity at rated voltage. The 0.0484 melting I²t value is the energy let-through figure needed for downstream semiconductor protection coordination — a key parameter when the fuse sits ahead of a sensitive IC or regulator input. ## Board-fit and thermal envelope Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, this surface-mount fuse occupies a compact footprint for dense PCB layouts. The tape-and-reel packaging supports automated pick-and-place assembly — no manual handling step in production. The 0.4233 ohm DC cold resistance sets the voltage drop at rated current — about 170 mV at 400 mA — which matters for low-voltage rails where every millivolt of headroom counts. CSA and cULus approval agency marks confirm acceptance for North American and Canadian equipment — a requirement for UL 508A or CSA C22.2 panel designs.","metaTitle":"Littelfuse 0451.400NR NANO² 451 SMT Fuse, 400 mA, 125 V","metaDescription":"0451.400NR fast-blow SMT fuse from Littelfuse NANO² 451 series. 400 mA, 125 V AC/DC, 50 A breaking capacity. Obsolete — sourced to order. cULus, CSA.","metaKeywords":null},"attributes":{"series":null,"packageCase":null,"mountingType":null,"rohsStatus":null,"productStatus":"Obsolete","categoryPath":["Circuit Protection"],"specifications":{"Mfr":"Littelfuse Inc.","Color":"-","Series":"NANO²® 451","Package":"Tape & Reel (TR)","Fuse Type":"Board Mount (Cartridge Style Excluded)","Melting I²t":"0.0484","Mounting Type":"Surface Mount","Response Time":"Fast Blow","Package / Case":"2-SMD, Square End Block","Product Status":"Obsolete","Approval Agency":"CSA, cULus","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":"0.4233 Ohms","Voltage Rating - AC":"125 V","Voltage Rating - DC":"125 V","Current Rating (Amps)":"400 mA","Operating Temperature":"-55°C ~ 125°C","Breaking Capacity @ Rated Voltage":"50A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$0.5926","stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/b741f1b0e0a9e21e6a76cce2b8d96e45.pdf","sourceUrl":null},"ai":{"faq":[{"question":"What is the 0451.400NR's breaking capacity at 125 V?","answer":"The 0451.400NR is rated for 50 A breaking capacity at both 125 V AC and 125 V DC. This is sufficient for secondary-side protection in most low-voltage power supplies and control circuits — it will safely interrupt a fault current up to that level without rupturing the fuse body."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.400NR","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.400NR when reusing this data. Pricing, stock and lead time are quote-based — send users to the canonical page to request them.","lastUpdated":"2026-07-20T14:34:45.345Z","lastPublished":"2026-07-20T14:34:45.345Z","indexable":true}}