{"schemaVersion":1,"slug":"27m-main-input-undervoltage-protection","name":"Main-input undervoltage protection","kind":"function","abbreviation":"27M","aliases":["main undervoltage","main input UV","ANSI 27M","IEEE 27M"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEEE / ANSI","Manufacturer"],"summary":"Supervises low voltage using the relay's main voltage measurement inputs.","description":["Supervises low voltage using the relay's main voltage measurement inputs.","The drafting record should connect this function to the main three-phase voltage inputs and their VT references, then trace the main undervoltage protection or control outputs. 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 (Eaton ETR family). Suffixes are not universal equivalences across products, and this reference supplies neither a protection setting nor certification of the selected scheme."],"readingNotes":["Identify the main three-phase voltage inputs and their VT references.","Trace the main undervoltage protection or control outputs."],"drawingChecklist":["Label the main three-phase voltage inputs and their VT references.","Cross-reference the main undervoltage protection or control outputs.","Retain the complete suffix, selected device tag and manufacturer manual revision."],"distinction":"Main-input 27M and auxiliary-input 27A can supervise different electrical nodes in the same relay.","facts":[{"label":"Function designation","value":"27M"},{"label":"Base function","value":"27 — Undervoltage"},{"label":"Published mapping","value":"Eaton ETR family"},{"label":"Suffix scope","value":"Application or manufacturer specific; check the complete drawing legend and selected device manual."}],"references":[{"sourceId":"pub-function-eaton-transformer","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":["27-undervoltage","voltage-transformer"],"artwork":"pub-function-box","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/protection-functions/27m-main-input-undervoltage-protection","illustration":{"url":"https://eloragrid.ai/library/illustrations/27m-main-input-undervoltage-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-eaton-transformer","title":"ETR-4000 and ETR-5000 transformer protection function tables","publisher":"Eaton","url":"https://www.eaton.com/us/en-us/catalog/electrical-circuit-protection/transformer-relays.html","type":"manufacturer","scope":"Public transformer-relay mappings including restrained/unrestrained differential, restricted ground differential, main and auxiliary voltage inputs, and measured/calculated earth-current inputs.","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."}]}