{"schemaVersion":1,"slug":"87n-neutral-differential-protection","name":"Neutral differential protection","kind":"function","abbreviation":"87N","aliases":["neutral current differential","neutral differential","ANSI 87N","IEEE 87N"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Identifies a differential scheme involving neutral or residual-current quantities as defined by the equipment documentation.","description":["Identifies a differential scheme involving neutral or residual-current quantities as defined by the equipment documentation.","The drafting record should connect this function to the neutral and phase/residual CT circuits and protected winding boundary, then trace the neutral differential operating element and earth-fault trip matrix. 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 and phase/residual CT circuits and protected winding boundary.","Trace the neutral differential operating element and earth-fault trip matrix."],"drawingChecklist":["Label the neutral and phase/residual CT circuits and protected winding boundary.","Cross-reference the neutral differential operating element and earth-fault trip matrix.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"The N suffix does not establish whether the scheme is high- or low-impedance restricted earth fault; record the actual scheme.","facts":[{"label":"Function designation","value":"87N"},{"label":"Base function","value":"87 — Differential protection"},{"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":["87-differential","current-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/87n-neutral-differential-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/87n-neutral-differential-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."}]}