# Wound-primary current transformer Canonical URL: https://eloragrid.ai/symbols/wound-primary-current-transformer Publisher: Elora Grid Updated: 2026-10-28 Lookup label: CT Drawing use: SLD, Schematic Reference families: IEC, Manufacturer CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy. ## In plain English ### What does Wound-primary current transformer mean? A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units. ### A simple example The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule. ### What the drawings help you do Check the short-time thermal rating against the fault level. Read primary terminals P1 and P2 for polarity. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary. ### This particular reference CT with a primary winding of several turns, used for low primary currents where a bar primary gives too little accuracy. A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary. ### Terms - Winding: A coil of conductor inside an electrical machine or transformer. - Rating: A value stating the conditions for which equipment is specified. - Schematic: A drawing showing function and connections rather than physical appearance. Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram. - [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) - [Current transformer symbol variants](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm) ## What it represents A wound-primary CT has a primary winding of more than one turn rather than a single bar or conductor through a window. This is needed at low primary currents, where a single turn would not produce enough magnetising ampere-turns for accurate metering, and it is common in MV metering units. The wound primary has a lower short-time withstand than a bar primary, so its thermal and dynamic ratings need checking against the fault level. The symbol shows the winding but not those ratings, which belong in the CT schedule. ## How to read it - Check the short-time thermal rating against the fault level. - Read primary terminals P1 and P2 for polarity. ## Information to show or reference - State ratio and class - Give short-time rating - Show polarity marks ## Important distinction A wound-primary CT has a multi-turn primary; a window or bar CT uses the circuit conductor as a single-turn primary. ## Facts - Primary: Multi-turn winding - Typical use: Low primary currents and metering units - Preview: Independent educational concept; consult the applicable standard and project legend for the exact graphic ## Public references - [Indoor current and voltage transformers](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) — ABB. Public manufacturer overview of indoor current and voltage instrument transformers. - [Current transformer symbol variants](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm) — Autodesk. Public AutoCAD Electrical current transformer family used for context; this variant is independently drawn. ## Graphic scope Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.