{"schemaVersion":1,"slug":"residual-connection-of-phase-cts","name":"Residual connection of phase CTs","kind":"symbol","abbreviation":"CT RES","aliases":[],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"A residual CT connection combines secondary currents from phase CTs to obtain a residual-current input.","description":["A residual CT connection combines secondary currents from phase CTs to obtain a residual-current input. This is a connection arrangement that should be drawn explicitly rather than assigned an unsupported separate standard-symbol number."],"readingNotes":["Match secondary polarity and CT characteristics across the connected phases.","The preview is an original explanation of this function. Match the actual drawing convention to its legend and the selected equipment documentation."],"drawingChecklist":["Show each phase CT","Identify residual summation node","Link earth-fault relay input"],"distinction":"Residual connection of three phase CTs is not the same physical sensor as a core-balance CT.","facts":[{"label":"Drawing role","value":"Current measurement"},{"label":"Representation scope","value":"Functional concept; not an official standard graphic or a product footprint"},{"label":"Identifier status","value":"The short label is a functional lookup label, not an assigned IEC or IEEE symbol number. Any separately listed Autodesk code is a verified vendor block name."}],"references":[{"sourceId":"autodesk-ct","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."},{"sourceId":"instrument-transformers","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."},{"sourceId":"pub-symbol-earth-fault","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."}],"related":["current-transformer","ct-test-terminal"],"artwork":"edu-residual-connection-of-phase-cts","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/symbols/residual-connection-of-phase-cts","illustration":{"url":"https://eloragrid.ai/library/illustrations/residual-connection-of-phase-cts.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"autodesk-ct","title":"Current transformer symbol variants","publisher":"Autodesk","url":"https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm","type":"cad-reference","scope":"Current transformers, secondaries and conductor indications; vendor block identifiers are distinct from IEC symbol identifiers.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."},{"id":"instrument-transformers","title":"Indoor current and voltage transformers","publisher":"ABB","url":"https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers","type":"manufacturer","scope":"Public current- and voltage-transformer product families. Ratings, terminals and dimensions depend on the model.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."},{"id":"pub-symbol-earth-fault","title":"Residual current and neutral-earthing protection context","publisher":"ABB","url":"https://new.abb.com/medium-voltage/digital-substations/campaigns/earth-fault-protection-portfolio/earth-fault-offering","type":"manufacturer","scope":"Public manufacturer explanation of the equipment function and selection context.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic."}]}