{"schemaVersion":1,"slug":"minimum-voltage-relay","name":"Minimum-voltage measuring relay","kind":"symbol","abbreviation":"K","aliases":["minimum voltage protection","undervoltage measuring relay","HCR1F35"],"category":"measurement-protection","drawingTypes":["Schematic","SLD"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Measuring relay that operates when voltage falls below a set level while some voltage is still present.","description":["The minimum-voltage relay form operates when the measured voltage falls below its setting. It is used for motor undervoltage tripping, load shedding and transfer schemes, where a sustained voltage dip indicates a supply problem rather than a momentary disturbance.","The symbol shows the voltage quantity and the less-than threshold but not the time delay, which phases are monitored or whether operation is blocked on VT fuse failure. Without a blocking input a blown VT fuse can cause an unwanted trip, so the supervision arrangement should be cross-referenced."],"readingNotes":["Check which phase voltages are monitored.","Look for VT supervision or fuse-failure blocking."],"drawingChecklist":["State threshold and delay","Show VT source","Reference blocking input"],"distinction":"A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.","facts":[{"label":"Measured quantity","value":"Voltage below a set level"},{"label":"Publisher reference token","value":"HCR1F35 (Autodesk identifier; not an IEC database ID)"},{"label":"Preview","value":"Independent educational concept; consult the publisher and applicable standard for the exact graphic"}],"references":[{"sourceId":"pub-symbol-voltage-relays","relevance":"Public AutoCAD Electrical relay listing that names the Minimum Voltage Protection block; the illustration is independently drawn."},{"sourceId":"iec-diagrams","relevance":"IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced."}],"related":["loss-of-voltage-monitoring-relay","27-undervoltage","voltage-transformer"],"artwork":"s28-minimum-voltage-relay","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","plainEnglish":{"title":"What does Minimum-voltage measuring relay mean?","introduction":"The minimum-voltage relay form operates when the measured voltage falls below its setting. It is used for motor undervoltage tripping, load shedding and transfer schemes, where a sustained voltage dip indicates a supply problem rather than a momentary disturbance.","example":"The symbol shows the voltage quantity and the less-than threshold but not the time delay, which phases are monitored or whether operation is blocked on VT fuse failure. Without a blocking input a blown VT fuse can cause an unwanted trip, so the supervision arrangement should be cross-referenced.","drawings":"Check which phase voltages are monitored. Look for VT supervision or fuse-failure blocking. A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.","terms":[{"name":"Coil","meaning":"A wound conductor that can produce a magnetic field when energised."},{"name":"Phase","meaning":"One of the related AC waveforms in a power system."},{"name":"Signal","meaning":"Electrical information passed between devices, rather than necessarily the main power supply."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"AutoCAD Electrical: Voltage monitoring relays","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm"},{"label":"IEC graphical symbols for diagrams","url":"https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/"}],"detail":"Measuring relay that operates when voltage falls below a set level while some voltage is still present. A minimum-voltage relay responds to a reduced voltage; a loss-of-voltage relay responds to absence of voltage.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/minimum-voltage-relay","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/minimum-voltage-relay.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"pub-symbol-voltage-relays","title":"AutoCAD Electrical: Voltage monitoring relays","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-5296749E-9336-4B07-9956-160963D6C848.htm","type":"cad-reference","scope":"Public vendor catalogue naming and functional variants. Vendor block names are not IEC identifiers. Linked for reference; no graphics or CAD files are redistributed.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public AutoCAD Electrical relay listing that names the Minimum Voltage Protection block; the illustration is independently drawn."},{"id":"iec-diagrams","title":"IEC graphical symbols for diagrams","publisher":"IEC","url":"https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/","type":"standard","scope":"IEC 60617 and related symbol-design publications. Full database access requires a subscription.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced."}]}