{"schemaVersion":1,"slug":"neutral-unbalance-relay-between-two-systems","name":"Neutral-unbalance relay between two polyphase systems","kind":"symbol","abbreviation":"K","aliases":["in neutral between two multi-phase systems","neutral interconnection current relay","HCR1F33"],"category":"measurement-protection","drawingTypes":["Schematic","SLD"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Relay form measuring current in a link joining the star points of two polyphase systems, such as split capacitor banks.","description":["This form shows a current relay in the conductor that joins the neutral points of two star-connected polyphase systems. A familiar application is the double-star capacitor bank, where a CT in the link between the two star points detects unbalance caused by failed capacitor units.","In a healthy balanced arrangement the link carries little current, so the relay setting is a small fraction of phase current and must allow for natural unbalance. The symbol does not tell you the alarm and trip stages or the compensation for inherent unbalance; those are in the bank protection settings."],"readingNotes":["Identify the two star points joined by the measured link.","Look for separate alarm and trip stages."],"drawingChecklist":["Show the interconnecting link and CT","State alarm and trip settings","Note inherent unbalance compensation"],"distinction":"This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.","facts":[{"label":"Measured quantity","value":"Current in a neutral interconnection between two systems"},{"label":"Publisher reference token","value":"HCR1F33 (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-current-relays","relevance":"Public AutoCAD Electrical relay listing that names the In Neutral between 2 Multi-Phase Systems block; the illustration is independently drawn."},{"sourceId":"iec-diagrams","relevance":"IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced."}],"related":["neutral-current-relay","60-voltage-or-current-balance-relay","current-transformer"],"artwork":"s28-neutral-unbalance-relay-between-two-systems","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","plainEnglish":{"title":"What does Neutral-unbalance relay between two polyphase systems mean?","introduction":"This form shows a current relay in the conductor that joins the neutral points of two star-connected polyphase systems. A familiar application is the double-star capacitor bank, where a CT in the link between the two star points detects unbalance caused by failed capacitor units.","example":"In a healthy balanced arrangement the link carries little current, so the relay setting is a small fraction of phase current and must allow for natural unbalance. The symbol does not tell you the alarm and trip stages or the compensation for inherent unbalance; those are in the bank protection settings.","drawings":"Identify the two star points joined by the measured link. Look for separate alarm and trip stages. This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.","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":"Rating","meaning":"A value stating the conditions for which equipment is specified."}],"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: Current monitoring relays","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.htm"},{"label":"IEC graphical symbols for diagrams","url":"https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/"}],"detail":"Relay form measuring current in a link joining the star points of two polyphase systems, such as split capacitor banks. This relay measures the link between two star points; a neutral-current relay measures one neutral path to earth or to the supply.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/neutral-unbalance-relay-between-two-systems","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/neutral-unbalance-relay-between-two-systems.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-current-relays","title":"AutoCAD Electrical: Current monitoring relays","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-E0DDA638-4664-4F1E-B191-29A4C40C4A0A.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 In Neutral between 2 Multi-Phase Systems 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."}]}