# Bushing current transformer

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

Toroidal CT mounted around a transformer or breaker bushing, often with a tapped multi-ratio secondary.

## In plain English

### What does Bushing current transformer mean?

A bushing CT is a toroidal core and secondary slipped over the bushing of a power transformer, generator or dead-tank circuit breaker. The bushing conductor is the primary, and several CTs may be stacked on one bushing for differential, overcurrent and metering duties.

### A simple example

Bushing CTs are often multi-ratio, with taps on the secondary, and only the selected tap should be wired to the relay. The symbol shows the location at the bushing, so the reader must check which side of the breaker or transformer the CT sits on to understand the protection zone overlap.

### What the drawings help you do

Identify which side of the device each bushing CT sits on. Check the selected tap on multi-ratio CTs. A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.

### This particular reference

Toroidal CT mounted around a transformer or breaker bushing, often with a tapped multi-ratio secondary. A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.

### Terms

- Winding: A coil of conductor inside an electrical machine or transformer.
- Coil: A wound conductor that can produce a magnetic field when energised.
- Terminal: An identified point where a conductor connects.

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)
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/)


## What it represents

A bushing CT is a toroidal core and secondary slipped over the bushing of a power transformer, generator or dead-tank circuit breaker. The bushing conductor is the primary, and several CTs may be stacked on one bushing for differential, overcurrent and metering duties.
Bushing CTs are often multi-ratio, with taps on the secondary, and only the selected tap should be wired to the relay. The symbol shows the location at the bushing, so the reader must check which side of the breaker or transformer the CT sits on to understand the protection zone overlap.

## How to read it

- Identify which side of the device each bushing CT sits on.
- Check the selected tap on multi-ratio CTs.

## Information to show or reference

- State selected tap and full ratio
- Show position relative to the breaker or winding
- Mark polarity

## Important distinction

A bushing CT uses the bushing conductor as its primary; a free-standing CT has its own insulated primary.

## Facts

- Mounting: Over a transformer or breaker bushing
- Common feature: Multi-ratio tapped secondary
- 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.
- [IEEE/ANSI 315-1975: graphic symbols for electrical and electronics diagrams](https://standards.ieee.org/ieee/315/515/) — IEEE Standards Association. IEEE graphic-symbol standards context; no standard glyph is reproduced.

## 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.