{"schemaVersion":1,"slug":"51n-time-neutral-overcurrent-protection","name":"Time neutral-overcurrent protection","kind":"function","abbreviation":"51N","aliases":["neutral IDMT","residual time overcurrent","ANSI 51N","IEEE 51N"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Supervises neutral or residual overcurrent with the configured timing characteristic.","description":["Supervises neutral or residual overcurrent with the configured timing characteristic.","The drafting record should connect this function to the neutral or residual measurement source and CT reference, then trace the neutral time-overcurrent output and earth-fault coordination reference. Keep the complete designation and equipment tag together so that the SLD, relay logic and terminal schedule describe the same implementation.","The cited mapping is a public manufacturer example (SEL public device-number table). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme."],"readingNotes":["Identify the neutral or residual measurement source and CT reference.","Trace the neutral time-overcurrent output and earth-fault coordination reference."],"drawingChecklist":["Label the neutral or residual measurement source and CT reference.","Cross-reference the neutral time-overcurrent output and earth-fault coordination reference.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"Neutral/residual 51N does not determine whether the source is a neutral CT or a residual sum; show the source explicitly.","facts":[{"label":"Function designation","value":"51N"},{"label":"Base function","value":"51 — Time overcurrent"},{"label":"Published mapping","value":"SEL public device-number table"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-sel-numbers","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"sourceId":"ieee-functions","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}],"related":["51-time-overcurrent","current-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/51n-time-neutral-overcurrent-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/51n-time-neutral-overcurrent-protection.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-function-sel-numbers","title":"ANSI device-number and suffix reference table","publisher":"Schweitzer Engineering Laboratories","url":"https://selinc.com/pt/products/tables/ansi/","type":"manufacturer","scope":"Public Portuguese-language base-number and application-suffix table. Used to cross-check public number associations. Application-specific and historical labels need the selected drawing legend; this table is not a substitute for the licensed IEEE standard.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public primary-source function or application mapping used to identify this designation; wording and drafting notes are original."},{"id":"ieee-functions","title":"IEEE C37.2-2022: power-system device function numbers","publisher":"IEEE","url":"https://ieeexplore.ieee.org/document/9984140","type":"standard","scope":"Device function numbers, acronyms and contact designations. The full publication may require access through IEEE.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Device-number and suffix convention. This page is not a reproduction of the full licensed standard."}]}