CT
Current transformer
A current-measurement transformer used with metering and protection equipment.
SLD / Schematic
Symbols · CT RES
Residual connection of phase CTs
A residual CT connection combines secondary currents from phase CTs to obtain a residual-current input.
SLD / Schematic · CT RES
What it represents
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.
How to read it
- 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.
Information to show or reference
- Show each phase CT
- Identify residual summation node
- Link earth-fault relay input
A distinction that matters
Residual connection of three phase CTs is not the same physical sensor as a core-balance CT.
Sources you can follow
These public references support the explanation and provide further detail. Their graphics and downloadable files remain with their publishers.
Current transformer symbol variants
Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic.
Indoor current and voltage transformers
Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic.
Residual current and neutral-earthing protection context
Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic.
About this graphic
This illustration was authored independently by Elora Grid to explain the concept. It is not reproduced from a customer drawing, an official standard graphic or a manufacturer CAD file. Its correspondence to an exact IEC or IEEE symbol identifier has not been certified.
SVG and DXF downloads contain this original artwork. DXF uses unscaled drawing units; a GA envelope supplies no product dimensions, clearances or fabrication information. Original artwork is available under CC BY 4.0. Third-party references retain their own terms.
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