# Arc-flash fibre loop sensor

Canonical URL: https://eloragrid.ai/symbols/arc-flash-fibre-loop-sensor
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: AF
Drawing use: SLD, Schematic
Reference families: Manufacturer

Bare optical fibre routed through switchgear that picks up arc light anywhere along its length.

## In plain English

### What does Arc-flash fibre loop sensor mean?

A fibre loop sensor is an unjacketed optical fibre routed through busbar chambers or along switchgear lines. Light from an arc anywhere along its length enters the fibre and reaches the arc-flash relay, so one loop can cover a large area that would need many point sensors.

### A simple example

Because the whole length is sensitive, a loop identifies the zone but not the exact compartment, and the trip zone therefore follows the routing. Loop length affects sensitivity, and the symbol does not show routing, length or the loop-check function, which should be recorded on the layout and schematic.

### What the drawings help you do

Read the routing drawing to see which compartments the loop crosses. Check that the trip zone matches the loop coverage. A fibre loop covers a long area without locating the arc precisely; a point sensor watches one compartment.

### This particular reference

Bare optical fibre routed through switchgear that picks up arc light anywhere along its length. A fibre loop covers a long area without locating the arc precisely; a point sensor watches one compartment.

### Terms

- Coil: A wound conductor that can produce a magnetic field when energised.
- Signal: Electrical information passed between devices, rather than necessarily the main power supply.
- Schematic: A drawing showing function and connections rather than physical appearance.

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.

- [SEL-C804 multimode arc-flash detection fibre-optic cables](https://selinc.com/products/c804/)


## What it represents

A fibre loop sensor is an unjacketed optical fibre routed through busbar chambers or along switchgear lines. Light from an arc anywhere along its length enters the fibre and reaches the arc-flash relay, so one loop can cover a large area that would need many point sensors.
Because the whole length is sensitive, a loop identifies the zone but not the exact compartment, and the trip zone therefore follows the routing. Loop length affects sensitivity, and the symbol does not show routing, length or the loop-check function, which should be recorded on the layout and schematic.

## How to read it

- Read the routing drawing to see which compartments the loop crosses.
- Check that the trip zone matches the loop coverage.

## Information to show or reference

- Show loop routing
- State loop length
- Reference relay channel

## Important distinction

A fibre loop covers a long area without locating the arc precisely; a point sensor watches one compartment.

## Facts

- Sensing element: Bare optical fibre
- Coverage: Entire routed length
- Preview: Functional illustration of the device role; not a product footprint or certified standard graphic

## Public references

- [SEL-C804 multimode arc-flash detection fibre-optic cables](https://selinc.com/products/c804/) — Schweitzer Engineering Laboratories. Public manufacturer page describing fibre arc-flash sensors for large areas such as bus compartments.

## 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.