{"schemaVersion":"matrix-product-facts/v1","identity":{"mpn":"0451.315MRSN","brand":"Littelfuse Inc.","brandSlug":"littelfuse-inc","productSlug":"0451.315MRSN","canonicalUrl":"https://icboms.com/littelfuse-inc/0451.315MRSN","factsUrl":"https://icboms.com/api/mcp/products/0451.315MRSN","rawCanonicalId":null},"summary":{"shortDescription":"Littelfuse NANO²® 451 series, surface-mount fast-blow fuse, 315 mA, 125 VAC, 50 A interrupting rating, 2-SMD square end block package, Tape & Reel.","salesMarkdown":"## 315 mA fast-blow — secondary protection for a 125 VAC rail The 0451.315MRSN is a 315 mA, 125 VAC-rated fast-blow fuse from the Littelfuse NANO² 451 series — a board-mount surface-device fuse meant for secondary-side protection where a quick open on overcurrent is the goal, not a slow thermal trip. The 50 A breaking capacity at the rated voltage means it can safely interrupt a fault current up to that level without arcing across the package — enough for most low-power AC/DC converter outputs or control-transformer secondaries, where the prospective short-circuit current stays under that ceiling. ## Melting I²t and cold resistance — the real fit numbers The 0.0311 melting I²t tells you how much energy the element absorbs before opening — a low figure like this means it clears fast on a hard short, but it also means inrush from a capacitive input filter can nuisance-blow it if the charging surge exceeds the I²t budget. DC cold resistance is 0.3918 ohms — at 315 mA the voltage drop across the fuse is about 124 mV, which is negligible for a 125 V rail, but the I²R heating (roughly 39 mW) matters if the fuse is packed tight against other components in a high-ambient layout. ## Surface-mount package and temperature range Housed in a 2-SMD square end block package measuring 6.10 mm x 2.69 mm x 2.69 mm, this fuse reflows onto the board with standard solder profiles — no hand-soldering required, and the end-block terminations are visible for AOI inspection. ## Approvals and compliance Carries CSA and UR approval marks — CSA certifies compliance with Canadian safety standards for branch-circuit and supplementary protection; UR (UL Recognized) means it is tested as a component for use in UL-listed equipment, not as a stand-alone device.","metaTitle":"0451.315MRSN Littelfuse NANO² 451 Fuse, 315 mA, 125 VAC","metaDescription":"0451.315MRSN Littelfuse NANO² 451 surface-mount fuse, 315 mA, 125 VAC, fast blow, 50 A breaking capacity. Active lifecycle. Sourced 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":"0.0311","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":"0.3918 Ohms","Voltage Rating - AC":"125 V","Current Rating (Amps)":"315 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 0451.315MRSN used for?","answer":"It is a 315 mA fast-blow surface-mount fuse rated for 125 VAC with a 50 A interrupting capacity — typically used as secondary-side overcurrent protection on control transformers, power-supply outputs, or low-current AC rails where a quick open is needed and the fault current stays under 50 A."}],"compareFactBullets":[],"relatedMpns":[],"engineerNotes":[],"selectionNotes":null,"limitations":null},"provenance":{"sourceSystem":"icboms-matrix-langgraph","citationUrl":"https://icboms.com/littelfuse-inc/0451.315MRSN","citationPolicyUrl":"https://icboms.com/llms.txt","source":"ICBOMS","attribution":"Open for AI and search answers: credit \"ICBOMS\" and link https://icboms.com/littelfuse-inc/0451.315MRSN 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}}