— A Practical Guide for Engineers, EPCs, and Project Teams

Cable trays are the backbone of industrial power and instrumentation distribution systems. They support and protect cables, facilitate efficient heat dissipation, and allow for future expansion and maintenance access-13. Unlike electrical conduit, which completely encloses cables, tray systems offer design flexibility, cost savings, and the ability to add or reconfigure circuits without major disruption-1.

However, selecting the wrong tray type, material, or size can lead to cable overheating, signal interference, insulation aging, and costly downtime-3. This guide provides a practical framework for selecting cable trays for industrial power and instrumentation systems, covering tray types, materials, sizing, fill capacity, and load considerations.

1. The Selection Framework: Start with the Cables

Before selecting a tray, you must understand what it will carry. Tray selection starts with a complete cable schedule-7:

Key questions to answer before selecting a tray-7 :

• What cable types, quantities, and outer diameters are being routed?

• Is this a power, control, instrumentation, or mixed-cable run?

• What is the signal sensitivity of the cables (instrumentation, telecom, fibre)?

• What future expansion is expected? 10–25% spare capacity is recommended.

• Are there separation requirements between power and signal cables?

The key principle: Tray selection is driven by load class (e.g., 100–200 kg/m), environment (indoor, outdoor, corrosive), cable type, and maintenance access needs-2. Engineers should start from the cable schedule and route geometry, then select the tray type that satisfies these constraints—rather than designing routes around a preselected tray-2.

2. Cable Tray Types: Matching the Tray to the Application

The Cable Tray Institute recognises six basic tray designs, but the three most common in industrial power and instrumentation systems are ladder, ventilated trough, and solid bottom-13-.

2.1 Ladder Cable Tray

Construction: Two longitudinal side rails connected by individual rungs or cross members-.

Key features-1-12:

• Maximum air circulation — allows heat produced in cable conductors to dissipate effectively, preventing premature ageing

• Rungs provide tie-down anchors — essential for single conductor cables; under fault conditions, magnetic forces can force single conductors out of the tray if not secured-12

• Cables may exit/enter through top or bottom

• Moisture cannot accumulate — prevents water from being piped into electrical equipment

• Minimal dust buildup — compared to ventilated trough or solid bottom

• Hazardous gases cannot be piped from one area to another

Support span: 12–20 feet-13.

Applications-2:

• Heavy-duty main power trunk lines-3

• Runs where cable mass exceeds 40–60 kg/m and spans reach 3–6 m

• Turbine halls, pipe racks, substation–MCC runs

• Approximately 75% of cable tray installations use ladder tray-11

Best for: Power cables, large control cables, long spans, heavy loads.

Note: Rung spacing affects small cable support. 9-inch rung spacing is common and supports all cable sizes without visible drooping. 12 or 18-inch spacing may allow small diameter cables to droop between rungs-12.

2.2 Ventilated Trough Cable Tray

Construction: Two side rails with a ventilated bottom containing perforations or slots-.

Key features-12:

• Provides free flow of air across cables for heat dissipation

• More cable support than ladder tray

• Perforations support cable tie anchoring

• Offers a balance between the open design of ladder trays and the protection of solid bottom trays-

Support span: 5–15 feet-13.

Applications-2:

• Control, instrumentation, and small power circuits

• Dense signal and precision monitoring circuits-3

• Mixed cable bundles where ventilation and support are both needed

Key consideration: The only reason to select a ventilated trough over a ladder tray is aesthetics, as the additional support is not significant-11. However, ventilated trays often cost less than ladder trays but do not offer as wide a support span-.

Best for: Control cables, instrumentation cables, mixed circuits, moderate loads.

2.3 Solid Bottom Cable Tray

Construction: Two side rails with a continuous solid sheet bottom-.

Key features-:

• Maximum cable protection — shields cables from dust, drips, and falling debris

• Provides physical enclosure and isolation-3

• Requires cutting the tray or using fittings to enter/exit cables-

Support span: 5–12 feet-13.

Applications-2:

• Dusty environments (transfer towers, chemical loading bays)

• Low-level signal routes near high-noise equipment (EMI concerns)

• Sensitive instrumentation and control cables

• Short runs where cable protection is critical

Critical limitation: Single conductor cables and Type MV cables are not allowed to be installed in solid bottom cable trays per NEC-11. Solid bottom trays are also not permitted in Class II, Division 2 hazardous locations (dust)-12.

Best for: Instrumentation cables, sensitive circuits, dusty environments, short runs.

2.4 Tray Type Quick Reference

3. Material Selection: Matching the Environment

Material selection should be based on environmental factors including exposure to moisture, chemicals, and temperature extremes-.

3.1 Metallic Trays

3.2 Non-Metallic Trays

3.3 Material Selection Quick Guide

4. Tray Sizing and Fill Capacity

Proper tray sizing ensures adequate space for cables, heat dissipation, and future expansion.

4.1 Fill Requirements per NEC

The National Electrical Code (NEC) Article 392.9 establishes specific fill limits based on tray type and cable application-23:

Critical note: The lower fill limit for solid bottom trays (40% vs 50%) is based on thermal management principles. Solid bottom trays restrict air circulation beneath cables, reducing cooling capacity. Ladder trays allow multi-sided convective cooling-23.

For solid-bottom multiconductor-only runs, use 40% instead of 50%-.

4.2 Tray Sizing Calculation

Step 1: Calculate total cable cross-sectional area

For each cable type:

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Cable Area = π × (Diameter/2)²

Sum the areas of all cables to be placed in the tray.

Step 2: Determine required tray area

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Required Tray Area = Total Cable Area ÷ Fill Percentage

Example-: If total cable area = 20,000 mm² and design fill = 40%, required internal area ≈ 20,000 ÷ 0.40 = 50,000 mm².

Step 3: Select tray width and depth

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Tray Area = Width × Usable Depth[reference:53]

General rule: Cable tray sizing is correct when it appears approximately 50% full of cable or wire-.

4.3 Spare Capacity

Industry best practice is to reserve 10–25% spare capacity for future additions-7. If future cable growth may exceed about 20%, design to the future load case instead of the day-one load-42.

5. Load and Support Span

5.1 Load Capacity

Tray load capacity depends on:

• Cable weight per metre (including future additions)

• Span length / support spacing

• Tray geometry (width, side height, thickness)

• Material (steel vs aluminium vs stainless)-7

Common design loads:

• Typical process plants: 50–200 kg/m uniformly distributed load-2

• Light wire basket (control/data): 25–40 kg/m-42

• Power cable ladder: 75–150 kg/m (requires deeper side rails and closer supports)-42

NEMA VE 1 requirements-:

• Each rung must support maximum cable load with a safety factor of 1.5

• Plus a 200-lb (90-kg) concentrated load when tested per NEMA VE 1

5.2 Support Spacing

Support distance is a key selection input because span affects bending stress, midspan deflection, and hanger reaction-42.

General principles-42:

• Set the real support spacing available from structure

• Calculate total distributed load: cables + tray self-weight + accessories

• Check whether covers, fittings, maintenance loads, or future fill change the design basis

• Select the tray system by tested span/load performance, not width alone

NEMA VE 1 Class Designation indicates support span in feet plus working load designation. Common support spans: 8, 12, 16, and 20 feet-.

For fittings: Supports should be placed within approximately 300–600 mm of major fittings (elbows, tees, reducers, vertical bends)-42.

6. Separation Requirements

Instrumentation cables must be separated from power cables to prevent interference-.

General separation principles-:

• Instrumentation cables shall be adequately separated from power wiring and electrical equipment

• Where parallel routing is required, maintain specified physical distances

• If required, instrumentation cables shall cross power cables at right angles with a minimum distance of 300 mm-

Key recommendations-:

• Instrumentation trays should always be at the bottom in stacked tray arrangements

• At least 12 inches (300 mm) of clear space between tray levels

7. Installation Best Practices

8. Why Choose Anhui Tiankang for Cable Tray Projects?

Anhui Tiankang (Group) Co., Ltd. has been manufacturing industrial instruments and cables for nearly five decades. Our comprehensive product portfolio supports complete cable tray system design:

Instrumentation and cable portfolio:

• Instrumentation cables: IS, OS, and IS+OS shielding configurations; PVC, LSZH, oil-resistant, and SHF2 sheaths

• Fire performance cables: IEC 60332 (flame retardant), IEC 60331 (fire resistant), hydrocarbon fire resistant

• Armoured cables: STA (steel tape), SWA (steel wire), and braided options

• Ex-certified cables: Intrinsically safe cables with low capacitance, blue LSZH sheath, Ex-ia certified

• Complete certifications: CCC Ex, ATEX, IECEx, CCS marine

Core advantages:

• CNAS-accredited laboratory: Full electrical, mechanical, and fire performance testing

• Complete product range: From instrumentation to cables to accessories—one-stop supply

• Proven track record: Long-term supplier to CNPC, Sinopec, CNOOC, and international EPC projects

9. Conclusion

Cable tray selection requires a systematic approach that balances cable type, environmental conditions, fill capacity, load requirements, and separation needs.

Key takeaways:

Remember: A properly designed and installed cable tray system will provide outstanding reliability for power, control, communication, and instrumentation systems-1. Poor tray structural matching, unreasonable layered partitioning, and ignored environmental adaptability can cause cable overheating, signal crosstalk, and insulation ageing-3.

Contact Us

For cable tray selection advice, technical documentation, or project quotations, please contact:

Yin Shuangjie
International Sales Manager
📧 Email: [email protected]
📱 WhatsApp / Zalo: +86 17856068126
🌐 Website: http://www.tiankang-global.com/

Anhui Tiankang – Your partner for reliable instrumentation and cable solutions.