{"schemaVersion":1,"slug":"core-balance-current-transformer","name":"Core-balance current transformer","kind":"symbol","abbreviation":"CBCT","aliases":["zero sequence current transformer","residual current transformer"],"category":"measurement-protection","drawingTypes":["SLD","Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"A core-balance CT measures residual current from the net magnetic effect of conductors passing through its window.","description":["A core-balance CT measures residual current from the net magnetic effect of conductors passing through its window. It is used with earth-fault protection where the conductor arrangement and sheath routing affect the measurement."],"readingNotes":["Verify the included conductors and cable-sheath treatment against the protection scheme.","The preview is an original explanation of this function. Match the actual drawing convention to its legend and the selected equipment documentation."],"drawingChecklist":["Identify enclosed conductors","Show polarity and relay input","Reference sheath-earthing detail"],"distinction":"A CBCT measures a combined residual quantity; a phase CT measures an individual conductor current.","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-core-balance-current-transformer","publishedOn":"2026-10-13","updatedOn":"2026-10-13","provenance":"independent-public-research","url":"https://eloragrid.ai/symbols/core-balance-current-transformer","illustration":{"url":"https://eloragrid.ai/library/illustrations/core-balance-current-transformer.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."}]}