Wire Duct / Trunking Symbol
Definition: The Wire Duct / Trunking symbol represents an open-top or slotted plastic or metal channel used in wiring diagrams to denote a cable management system that organises, routes, and protects multiple conductors inside electrical panels, control cabinets, and industrial machinery enclosures, in compliance with IEC 61084 and NEMA standards.
Also known as: cable duct, wire trunking, cable trunking, panduit duct, wireway, cable channel, slotted duct, DIN duct.
What the Wire Duct / Trunking symbol means
The Wire Duct / Trunking symbol identifies the cable management channel through which control wiring, signal cables, and power conductors are bundled and routed inside an electrical enclosure. In a wiring diagram it marks the routing path between terminal blocks, PLCs, drives, and other panel components, indicating that cables run inside a protective trough rather than being routed individually.
Wire ducts simplify panel construction by keeping wiring neat, accessible, and mechanically protected. The symbol's two terminals—Left and Right—represent the entry and exit points of the duct run, allowing the diagram to show how wiring flows from one section of the panel to another without tracing every individual conductor.
How to identify the Wire Duct / Trunking symbol
The symbol is drawn as a horizontal rectangle with open-top slots (comb-like lines along the top edge) or as a plain rectangular channel, representing a cross-section or plan view of the duct. The Left terminal is at the left end and the Right terminal is at the right end of the duct run. Dashed lines may indicate concealed or enclosed duct sections. In panel layout drawings the duct is shown as a rectangle alongside DIN rails and terminal strips.
Function in a circuit
Wire duct provides mechanical protection, electrical separation, and organised routing for conductors inside electrical enclosures. The slotted sides allow individual wires to exit the duct at any point along its length, connecting to terminals, contactors, and devices mounted on nearby DIN rails. Duct fill capacity—typically 40–60% of cross-sectional area—must not be exceeded to maintain heat dissipation and allow future cable additions. Separate ducts are commonly used for power and signal/control wiring to minimise electromagnetic interference.
Standards: IEC vs ANSI
| IEC 60617 | IEC 61084-1 (cable management systems for electrical installations) and IEC 61084-2-1 (cable trunking systems) govern the dimensional, mechanical, and electrical requirements for cable trunking and ducts used in buildings and industrial enclosures. |
|---|---|
| ANSI/IEEE 315 | UL 2024 (optical fiber raceways) and NEMA 250/UL 508A cover wireway and panel wiring duct requirements in North America. NEC Article 376 governs metal wireways and Article 378 covers non-metallic wireways installed in buildings. |
| Key difference | IEC 61084 uses the term 'cable trunking system' and specifies IP-rated enclosure types; NEC/UL uses 'wireway' and 'wiring duct' with fill calculations based on conductor cross-sectional area. The physical components and installation principles are functionally identical. |
Terminals / pins
| Pin | Name |
|---|---|
| left | Left |
| right | Right |
Typical values
Common sizes: 25×25 mm, 40×40 mm, 60×60 mm, 80×80 mm, 100×100 mm (W×H); typical fill capacity: 40–60% of internal cross-sectional area; material: PVC (standard) or halogen-free FR PVC; fire rating: UL 94 V-0 or IEC 60695-11-10; slot pitch: 12–25 mm; standard lengths: 2 m per section.
Where the Wire Duct / Trunking symbol is used
- PLC control panels routing control wiring between I/O terminal strips and PLC modules
- Motor control centres (MCCs) organising power and control cables between contactors, overloads, and terminal blocks
- Industrial machine control cabinets separating sensor signal wiring from 24 V DC control wiring
- Building automation panel wiring between BACnet controllers and field device terminals
- Relay panels in power substations bundling protection and control relay wiring
- Test and measurement equipment racks organising interconnect cables between instruments
Example
In an industrial VFD panel layout drawing, two wire-duct runs appear horizontally between the terminal strip on the left and the VFD and PLC modules on the right; the upper duct (40×60 mm) carries 24 V control wiring and the lower duct (60×60 mm) carries motor power cables, keeping control and power circuits separated to minimise EMI as required by IEC 61000-5-2.
Key facts
- The Wire Duct / Trunking symbol has two terminals: Left and Right, representing the entry and exit ends of the duct run through which conductors are routed.
- Standard panel wire duct fill should not exceed 40–60% of the duct's internal cross-sectional area to maintain adequate heat dissipation and allow future additions.
- IEC 61084 governs cable trunking systems; in North America, NEC Article 376 (metal wireway) and Article 378 (non-metallic wireway) apply.
- Power and control/signal wiring should be routed in separate ducts whenever possible to prevent electromagnetic interference from power conductors coupling into low-level signal cables.
- Wire duct is typically installed horizontally and vertically along DIN-rail sections, with 90° corners, T-junctions, and end caps completing the routing system.
- Slotted wire duct allows conductors to exit at any point along the duct length; solid-wall duct (without slots) is used when conductors must not exit until the end of the run.
- UL 508A requires that wire duct used inside industrial control panels be listed and that the fill not exceed 40% of the duct cross-sectional area for power wiring.
Frequently asked questions
What does the wire duct symbol mean in a wiring diagram?
The wire duct (trunking) symbol represents a cable management channel inside an electrical panel or enclosure. It indicates that all conductors shown entering or exiting the symbol are physically routed inside that duct, keeping them organised, protected, and accessible.
What does a wire duct or trunking symbol look like in a schematic?
The symbol appears as a horizontal rectangle with open-top slots (comb-like lines) or as a plain rectangular channel, with Left and Right terminals at each end. In panel layout drawings it is shown as a rectangle running alongside DIN-rail strips and terminal blocks.
What is the maximum fill for a wire duct inside an electrical panel?
The maximum recommended fill for wire duct is 40–60% of the duct's internal cross-sectional area. UL 508A limits power wiring fill to 40% for industrial control panels; lower fill leaves room for heat dissipation and future cable additions.
What standard governs wire duct and cable trunking?
IEC 61084-1 and IEC 61084-2-1 govern cable trunking systems internationally. In North America, NEC Article 376 (metal wireways) and Article 378 (non-metallic wireways) apply for building installations, and UL 508A covers wire duct inside industrial control panels.
What is the difference between wire duct and conduit?
Wire duct is an open-top or slotted channel mounted inside enclosures, designed for easy conductor access and exit at any point along its length. Conduit is a closed pipe for protecting conductors routed between enclosures or through walls; conductors must be pulled through conduit and cannot exit except at fittings.
Why are power and control cables run in separate wire ducts?
Power cables (especially from variable-frequency drives and contactors) generate electromagnetic interference that can corrupt low-level signals in control and sensor cables. Running them in separate ducts—ideally spaced at least 50–100 mm apart—reduces inductive and capacitive coupling per IEC 61000-5-2 EMC installation guidelines.
How many terminals does the wire duct symbol have?
The wire duct symbol has two terminals: Left and Right, representing the two ends of the duct run. Conductors enter and exit the duct at these points (and through slots along its length), but the symbol itself only marks the routing path, not individual conductor connections.
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