{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.400MRSN","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.400MRSN","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.400MRSN","factsUrl":"https://icboms.com/api/mcp/products/0451.400MRSN","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse NANO²® 451 Series, Board Mount SMD Fuse, 0451.400MRSN, 400 mA, 125 VAC, 50 A Breaking Capacity, Fast Blow, 2-SMD Square End Block Package, Tape & Reel.","salesMarkdown":"## 400 mA fast-blow SMD fuse — the selection parameters that decide the fit The 0451.400MRSN is a 400 mA fast-blow fuse in Littelfuse's NANO² 451 series, housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm. This is a surface-mount board-level fuse — not a cartridge style — designed to protect a secondary circuit or a single load on a PCB. The 50 A breaking capacity at 125 VAC means this fuse can safely interrupt a fault current up to 50 A without rupturing the package or sustaining an arc. For a 400 mA fuse, 50 A is a high interrupt rating — it clears a short-circuit fault with margin, protecting downstream traces and components from the fault energy. The DC cold resistance of 0.56 Ohms is the resistance of the fuse element at 25°C. ## Thermal and environmental envelope The 125°C upper limit means the fuse element does not derate significantly in a warm enclosure or near a power component — the melting point of the alloy is well above the ambient ceiling. CSA and UR approval agency marks confirm acceptance for North American and Canadian equipment. These are not optional — a UL-listed fuse is often a requirement for UL 508A industrial control panels or UL 60950-1 ITE equipment. The UR mark (UL Recognized Component) means the fuse is tested to UL 248-14 for supplemental fuses. ## Lifecycle and supply posture — active, no end-of-life pressure Sourced through independent distribution channels against an RFQ.","metaTitle":"Littelfuse 0451.400MRSN NANO² 451 SMD Fuse, 400 mA, 125 VAC","metaDescription":"0451.400MRSN from Littelfuse — 400 mA fast-blow SMD fuse in the NANO² 451 series. 125 VAC, 50 A breaking capacity, 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)","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":"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":"0.56 Ohms","Voltage Rating - AC":"125 V","Current Rating (Amps)":"400 mA","Operating Temperature":"-55°C ~ 125°C","Breaking Capacity @ Rated Voltage":"50A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$1.4614","stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/604a0e4c498aa97d2607992508357d04.pdf","sourceUrl":null},"ai":{"faq":[{"question":"What is the 0451.400MRSN used for?","answer":"The 0451.400MRSN is a 400 mA fast-blow surface-mount fuse used to protect a single load or secondary circuit on a PCB from overcurrent and short-circuit faults. Common applications include power supply outputs, motor drive control boards, battery management systems, and telecom line cards where board-level protection is required."},{"question":"What is the breaking capacity of the 0451.400MRSN?","answer":"The breaking capacity is 50 A at 125 VAC. This is the maximum fault current the fuse can safely interrupt at its rated voltage without rupturing the package or sustaining an arc. For a 400 mA fuse, 50 A is a high interrupt rating — it clears a dead short with margin."},{"question":"What approvals does the 0451.400MRSN carry?","answer":"The fuse carries CSA and UR (UL Recognized Component) approval marks. The UR mark indicates testing to UL 248-14 for supplemental fuses, which is commonly required for UL 508A industrial control panels and UL 60950-1 ITE equipment. The CSA mark confirms acceptance for Canadian equipment."},{"question":"Where can I buy the 0451.400MRSN and how do I get a price?","answer":"Submit an RFQ (request for quote) to confirm current availability and pricing."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.400MRSN","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.400MRSN 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}}