# Core-balance current transformer

Canonical URL: https://eloragrid.ai/symbols/core-balance-current-transformer
Publisher: Elora Grid
Updated: 2026-10-13
Lookup label: CBCT
Drawing use: SLD, Schematic
Reference families: IEC, Manufacturer

A core-balance CT measures residual current from the net magnetic effect of conductors passing through its window.

## What it represents

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.

## How to read it

- 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.

## Information to show or reference

- Identify enclosed conductors
- Show polarity and relay input
- Reference sheath-earthing detail

## Important distinction

A CBCT measures a combined residual quantity; a phase CT measures an individual conductor current.

## Facts

- Drawing role: Current measurement
- Representation scope: Functional concept; not an official standard graphic or a product footprint
- Identifier status: 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.

## Public references

- [Current transformer symbol variants](https://help.autodesk.com/cloudhelp/2021/ENU/AutoCAD-Electrical/files/GUID-40AAEF4A-AC3F-4B3D-90A5-A9E0707C1241.htm) — Autodesk. 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](https://www.abb.com/gb/en/areas/electrification/medium-voltage/grid-components/core-components/indoor-instrument-transformers) — ABB. 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](https://new.abb.com/medium-voltage/digital-substations/campaigns/earth-fault-protection-portfolio/earth-fault-offering) — ABB. Public documentation of this equipment function or named vendor variant; the illustration is independently authored and is not the source graphic.

## 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.