# Optical current sensor

Canonical URL: https://eloragrid.ai/symbols/optical-current-sensor
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: OCT
Drawing use: SLD
Reference families: IEC, Manufacturer

Current sensor using light in an optical fibre around the conductor, whose polarisation changes with the magnetic field.

## In plain English

### What does Optical current sensor mean?

An optical current sensor measures current from the rotation of polarised light in a fibre wound around the conductor, a magneto-optic effect proportional to the enclosed magnetic field. It is used in higher-voltage and DC applications where conventional CTs are bulky or where saturation and insulation are concerns.

### A simple example

The sensor head connects through fibre to an electronics unit, which usually outputs digital sampled values to protection and metering devices. The symbol does not show the electronics unit, its supply or the data interface, all of which must be drawn for the measurement chain to be complete.

### What the drawings help you do

Find the electronics unit that converts the optical signal. Check the data interface to protection devices. An optical current sensor uses light in fibre; a conventional CT uses magnetic induction in a winding.

### This particular reference

Current sensor using light in an optical fibre around the conductor, whose polarisation changes with the magnetic field. An optical current sensor uses light in fibre; a conventional CT uses magnetic induction in a winding.

### Terms

- DC: Direct current: electricity flowing in one direction.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- 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)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

An optical current sensor measures current from the rotation of polarised light in a fibre wound around the conductor, a magneto-optic effect proportional to the enclosed magnetic field. It is used in HV and DC applications where conventional CTs are bulky or where saturation and insulation are concerns.
The sensor head connects through fibre to an electronics unit, which usually outputs digital sampled values to protection and metering devices. The symbol does not show the electronics unit, its supply or the data interface, all of which must be drawn for the measurement chain to be complete.

## How to read it

- Find the electronics unit that converts the optical signal.
- Check the data interface to protection devices.

## Information to show or reference

- Show sensor head and electronics
- Reference output interface
- State auxiliary supply

## Important distinction

An optical current sensor uses light in fibre; a conventional CT uses magnetic induction in a winding.

## Facts

- Principle: Magneto-optic rotation of polarised light
- Output: Usually digital via an electronics unit
- Preview: Functional illustration of the device role; not a product footprint or certified standard 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.
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC context for graphical symbols used in diagrams; no IEC graphic 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.