Cable Tray Symbol
Definition: The Cable Tray symbol represents a continuous rigid structural system — standardised under IEC 61537 and NEMA FG1 / UL 568 — used in electrical installation drawings to show the routing path of multiple cables along walls, ceilings, or floor structures without individual conduit, depicted as a rectangular ladder or perforated channel cross-section.
Also known as: cable tray, cable ladder, cable raceway, perforated cable tray, wire basket tray, cable runway.
What the Cable Tray symbol means
The Cable Tray symbol indicates a dedicated physical pathway for grouping and supporting multiple cables along a building, industrial plant, or data centre route. Unlike conduit, cable tray is an open system that allows cables to be added, inspected, or re-routed without dismantling the installation. It appears in electrical layout drawings and one-line diagrams to define the cable routing infrastructure before individual cable runs are drawn into it.
In building services and industrial drawings the symbol is annotated with tray width (e.g. 150 mm, 300 mm, 600 mm), tray type (ladder, perforated, solid-bottom, wire basket), and material (steel, aluminium, fibreglass). Engineers use it for cable ampacity derating calculations, as NEC 392 and IEC 61537 specify reduced current ratings when cables are bundled in a tray.
How to identify the Cable Tray symbol
The cable tray symbol is drawn as a horizontal rectangle with two parallel horizontal lines (the side rails) connected by regularly spaced short vertical or diagonal cross-members (the rungs or perforations), representing the cross-section or plan view of the tray. The left pin (Left) and right pin (Right) indicate the cable entry/exit ends of the tray section. In plan-view drawings the tray appears as a wide dashed or double-line rectangle spanning the route.
Function in a circuit
A cable tray mechanically supports and organises multiple cables along a common route, maintaining physical separation between power and signal cables where required, protecting cables from mechanical damage, and providing a continuous earth-bonded metallic pathway. It allows open-air cooling of cables (improving ampacity versus enclosed conduit), simplifies future additions, and provides a labelled route for maintenance identification.
Standards: IEC vs ANSI
| IEC 60617 | IEC 61537 specifies cable tray systems and cable ladder systems, covering mechanical performance, dimensions, corrosion protection, and testing. The symbol follows IEC 60617 installation drawing conventions. IEC 60364-5-52 covers current-carrying capacity correction factors for cables installed in trays. |
|---|---|
| ANSI/IEEE 315 | NEMA FG1 covers fibreglass cable tray; NEMA VE1 covers metallic cable tray. UL 568 lists metallic cable tray. NEC Article 392 (NFPA 70) governs cable tray installation requirements in North America, including fill calculations, support spacing, and earthing. |
| Key difference | IEC drawings use a cross-section or simplified plan symbol showing the tray outline and rungs. US/ANSI drawings often use a heavier double-line or hatched rectangle with a text label giving tray designation. IEC 61537 and NEMA VE1 have equivalent but separately written mechanical test criteria. |
Terminals / pins
| Pin | Name |
|---|---|
| left | Left |
| right | Right |
Typical values
Tray widths: 50 mm to 900 mm (IEC) or 3 in to 36 in (ANSI). Tray depths: 50 mm to 150 mm. Rung spacing (ladder type): 150 mm or 300 mm. Load ratings: light (50 kg/m), medium (75 kg/m), heavy (100 kg/m). Material: hot-dip galvanised steel, aluminium, stainless steel, or fibreglass (GRP). Maximum ambient temperature varies by material.
Where the Cable Tray symbol is used
- Industrial plants and process facilities — routing power, control, and instrument cables from MCC to field equipment
- Data centres — overhead cable ladders separating structured cabling from power distribution
- Commercial building services — corridor and ceiling cable management for HVAC, BMS, and electrical distribution
- Power stations and substations — heavy-duty cable ladders carrying HV cables between switchgear and transformers
- Marine and offshore platforms — corrosion-resistant GRP trays in hazardous or wet areas
- Tunnel and transportation infrastructure — fire-rated and smoke-retardant cable tray in transit tunnels
- Renewables — cable trays routing DC strings and AC combiner cables in large solar PV plants
Example
In a petrochemical plant electrical layout drawing, a cable tray symbol spans the length of a process module from the MCC room (left pin) to the motor junction boxes (right pin), annotated '300W × 75D HDG ladder tray, IEC 61537 Class B, on 3-metre centres'; individual cable runs are then cross-referenced to this tray in the cable schedule.
Key facts
- A cable tray is an open cable management system that supports and routes multiple cables; it is standardised under IEC 61537 (international) and NEMA VE1 / NEC Article 392 (North America).
- The symbol has two pins: Left and Right, representing the two ends of the tray section as it routes cables between connection points.
- Types include ladder tray (rungs only, best for large power cables), perforated tray (sheet with holes, good for mixed cable types), solid-bottom tray (no ventilation, for instrument cables), and wire basket (for data/low-voltage).
- Cable ampacity must be derated when cables are bundled in a tray — IEC 60364-5-52 and NEC 310.15 provide correction factors based on the number of conductors and tray type.
- Metallic cable tray must be continuously bonded to the electrical earth system; it may serve as the equipment grounding conductor in North American installations under NEC 392.60.
- Tray widths are standardised: 100 mm, 150 mm, 200 mm, 300 mm, 450 mm, 600 mm (IEC); 4", 6", 9", 12", 18", 24", 30", 36" (ANSI).
- Separation requirements mandate minimum 200 mm (or a solid barrier) between HV power trays and instrumentation/signal trays to prevent electromagnetic interference.
Frequently asked questions
What does the cable tray symbol mean in an electrical drawing?
The cable tray symbol represents the physical routing infrastructure for groups of cables. It shows where multiple cables will be run together along a common support structure — walls, ceilings, or floors — without individual conduit. The symbol is annotated with tray width, type, and material so the installer can procure and install the correct tray system.
What does the cable tray symbol look like?
The cable tray symbol is drawn as a rectangular outline with two parallel side rails connected by short cross-members (rungs) for a ladder tray, or as a rectangle with a dotted or perforated pattern for a perforated tray. The left and right pins mark the cable entry and exit ends of the tray section.
What is the difference between cable tray and conduit?
A cable tray is an open support system that holds cables without enclosing them, allowing easy access, addition, and removal of cables and providing better heat dissipation. Conduit fully encloses cables in a tube, providing mechanical protection and suitability for damp or hazardous locations, but requires more effort to add or replace cables.
What standard governs cable tray?
IEC 61537 is the primary international standard for cable tray and cable ladder systems, covering mechanical performance, load ratings, and corrosion testing. In North America, NEMA VE1 covers metallic tray and NEC Article 392 (NFPA 70) governs installation requirements including fill, support, and grounding.
How do I calculate cable tray fill?
NEC 392.22 limits the total cross-sectional area of cables in a cable tray based on tray width and cable type. For single-conductor cables 1000 kcmil and smaller, the sum of cable diameters must not exceed the tray width. IEC 61537 uses a fill factor approach based on the ratio of cable cross-section to tray cross-section, typically limited to 40–50% fill.
Does a metallic cable tray need to be earthed?
Yes. Metallic cable tray must be bonded to the electrical earth system at both ends and at intervals along its length. In North American installations, properly bonded metallic cable tray may serve as the equipment grounding conductor under NEC 392.60, provided it meets the minimum cross-section requirements for the circuit fault current.
What is the difference between IEC and ANSI cable tray standards?
IEC 61537 and NEMA VE1 both specify mechanical load testing, but use different test methods and classification categories. IEC 61537 defines three load classes (light, medium, heavy) with specific uniform distributed load values. NEMA VE1 uses a different load-deflection test. The physical dimensions and installation requirements also differ slightly between the two standards.
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