# Multi-core current transformer

Canonical URL: https://eloragrid.ai/symbols/multi-core-current-transformer
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: CT
Drawing use: SLD, Schematic
Reference families: IEC, Manufacturer

CT with several independent magnetic cores on one primary, each with its own secondary for metering or protection.

## In plain English

### What does Multi-core current transformer mean?

A multi-core CT has one primary passing through two or more separate cores, each with its own secondary winding. Typical MV and higher-voltage CTs have one metering core and one or more protection cores, so the single-line diagram shows each core as its own ring on the primary with its ratio and class beside it.

### A simple example

Separate cores mean a fault-saturated protection core does not disturb the metering core, and each can have a different accuracy class. The symbol shows how many cores exist but not which relay or meter each feeds, so every core needs its own designation and cross-reference.

### What the drawings help you do

Count the cores and read each ratio and class separately. Follow each secondary to its own relay or meter. A multi-core CT has separate magnetic cores; a CT with two secondaries on a common core shares one magnetic circuit.

### This particular reference

CT with several independent magnetic cores on one primary, each with its own secondary for metering or protection. A multi-core CT has separate magnetic cores; a CT with two secondaries on a common core shares one magnetic circuit.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Coil: A wound conductor that can produce a magnetic field when energised.
- Rating: A value stating the conditions for which equipment is specified.

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 multi-core CT has one primary passing through two or more separate cores, each with its own secondary winding. Typical MV and HV CTs have one metering core and one or more protection cores, so the single-line diagram shows each core as its own ring on the primary with its ratio and class beside it.
Separate cores mean a fault-saturated protection core does not disturb the metering core, and each can have a different accuracy class. The symbol shows how many cores exist but not which relay or meter each feeds, so every core needs its own designation and cross-reference.

## How to read it

- Count the cores and read each ratio and class separately.
- Follow each secondary to its own relay or meter.

## Information to show or reference

- Label each core
- State ratio and class per core
- Cross-reference each secondary circuit

## Important distinction

A multi-core CT has separate magnetic cores; a CT with two secondaries on a common core shares one magnetic circuit.

## Facts

- Construction: Separate cores on one primary
- Typical split: Metering core plus protection cores
- 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.