# Fused connection unit plan mark

Canonical URL: https://eloragrid.ai/symbols/fused-connection-unit-plan-mark
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: FCU
Drawing use: GA
Reference families: IEC

Plan mark for a fused connection unit that feeds fixed equipment through a cartridge fuse instead of a plug.

## In plain English

### What does Fused connection unit plan mark mean?

A fused connection unit, often called a fused spur, connects a fixed appliance such as a towel rail, extractor fan or boiler directly to a final circuit through a small cartridge fuse. Plans commonly draw a small square with an S-shaped fuse mark or the letters FCU at the wall line, sometimes with a switch stroke for the switched type.

### A simple example

The symbol is common in British-style layouts on ring final circuits, where fixed loads must be fused down from the circuit rating. The reader should check the fuse rating and whether a flex outlet is fitted on the front or the cable leaves from the back of the box.

### What the drawings help you do

It is not a socket outlet: no plug is involved. It also does not provide isolation suitable for mechanical maintenance unless the specification says so.

### This particular reference

Plan mark for a fused connection unit that feeds fixed equipment through a cartridge fuse instead of a plug. A switched socket outlet accepts a plug; a fused connection unit is wired to fixed equipment.

### Terms

- Normally open / normally closed: The contact state in the normal condition defined for the drawing.
- Terminal: An identified point where a conductor connects.
- 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.

- [Electrical installation design methodology and references](https://www.electrical-installation.org/enwiki/General_rules_of_electrical_installation_design)
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/)


## What it represents

A fused connection unit, often called a fused spur, connects a fixed appliance such as a towel rail, extractor fan or boiler directly to a final circuit through a small cartridge fuse. Plans commonly draw a small square with an S-shaped fuse mark or the letters FCU at the wall line, sometimes with a switch stroke for the switched type.
The symbol is common in British-style layouts on ring final circuits, where fixed loads must be fused down from the circuit rating. The reader should check the fuse rating and whether a flex outlet is fitted on the front or the cable leaves from the back of the box.
It is not a socket outlet: no plug is involved. It also does not provide isolation suitable for mechanical maintenance unless the specification says so.

## How to read it

- Read the fuse rating written beside the symbol, often 3 A or 13 A.
- Check whether the switched or unswitched version is required.

## Information to show or reference

- State fuse rating and switched or unswitched type.
- Name the fixed appliance it serves.
- Show the flex outlet or rear cable entry.

## Important distinction

A switched socket outlet accepts a plug; a fused connection unit is wired to fixed equipment.

## Facts

- Typical loads: Towel rails, extract fans, boilers, hand dryers
- Protection: Cartridge fuse in the accessory
- Preview: Independent educational concept; plan symbols for this device vary between legends, so read the project key

## Public references

- [Electrical installation design methodology and references](https://www.electrical-installation.org/enwiki/General_rules_of_electrical_installation_design) — Schneider Electric — Electrical Installation Guide. Installation design methodology context: circuits, outlets and final distribution are planned before symbols are placed.
- [IEC graphical symbols for diagrams](https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/) — IEC. IEC committee context for graphical symbols used in diagrams and installation documents; not a source of reproduced artwork.

## 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.