{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.800MR","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.800MR","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.800MR","factsUrl":"https://icboms.com/api/mcp/products/0451.800MR","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse Inc. NANO²® 451 series, Board Mount (Cartridge Style Excluded) fuse, 0451.800MR, 800 mA, 125 VAC/DC, Fast Blow, 2-SMD square end block, 50 A breaking capacity.","salesMarkdown":"## 800 mA fast-blow SMD fuse — what the ratings mean for the BOM The Littelfuse 0451.800MR is a NANO²® 451 series surface-mount fuse rated 800 mA at 125 VAC and 125 VDC. The 50 A breaking capacity at rated voltage means it can safely interrupt a short-circuit fault up to 50 A without rupturing or sustaining an arc — that is the number that matters for the secondary-side protection of a DC-DC converter or a low-voltage power rail. The fast-blow response time clears the overcurrent in under a few milliseconds at high fault multiples, which keeps downstream silicon safe during a hard short. The 0.271 melting I²t figure tells you the thermal energy the fuse absorbs before opening — useful for coordinating with the I²t rating of the PCB trace or the MOSFET it protects. ## Obsolete — sourcing what is left Littelfuse has marked the 0451.800MR as obsolete. That means the only supply channel is independent surplus and broker inventory — the part is not being made anymore, so whatever is in the distribution pipeline is what exists. For a BOM that already uses this fuse, the procurement move is to source it through an independent distributor that can verify authenticity and lot traceability. No pin-compatible drop-in replacement from Littelfuse is documented, so a redesign to a current-production NANO²® 451 variant or a different series may be needed for long-term supply. ## Board-fit and approvals The 2-SMD square end block package measures 6.10 mm x 2.69 mm x 2.69 mm — a compact footprint for dense PCB layouts. CSA and UL approvals mean the fuse is accepted for use in equipment sold into North American and Canadian markets — the UL listing covers the safety interrupt rating, and CSA is the Canadian equivalent.","metaTitle":"Littelfuse 0451.800MR NANO² 451 Fuse, 800 mA, 125 V","metaDescription":"Littelfuse 0451.800MR NANO²® 451 surface-mount fuse, 800 mA, 125 VAC/DC, fast blow, 50 A breaking capacity. Obsolete — sourced to order against an RFQ.","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":"0.271","Mounting Type":"Surface Mount","Response Time":"Fast Blow","Package / Case":"2-SMD, Square End Block","Product Status":"Obsolete","Approval Agency":"CSA, UL","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":"0.212 Ohms","Voltage Rating - AC":"125 V","Voltage Rating - DC":"125 V","Current Rating (Amps)":"800 mA","Operating Temperature":"-55°C~125°C","Breaking Capacity @ Rated Voltage":"50A"}},"commercial":{"minOrderQty":null,"leadTime":null,"referencePrice":"$2.7000","stockQuantity":0,"priceTiers":null},"links":{"datasheetUrl":"https://cdn.icboms.com/604a0e4c498aa97d2607992508357d04.pdf","sourceUrl":null},"ai":{"faq":[{"question":"Where can I buy the 0451.800MR and check current pricing?","answer":"Submit a request and we will quote the quantity you need against the available surplus inventory."},{"question":"What is the closest alternative to the 0451.800MR in the NANO² 451 series?","answer":"Littelfuse does not list an official successor for the 0451.800MR. A current-production NANO²® 451 fuse with the same 800 mA rating and 125 V rating would be a functional replacement, but the package and footprint should be verified against the existing PCB layout before ordering."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.800MR","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.800MR 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}}