Size of the reserved opening for the cable tray

The reserved opening for a cable tray should generally be slightly larger than the tray itself, typically allowing an extra 2 to 4 inches (50–100 mm) on each side to accommodate installation, thermal expansion, and future cable additions.

Practical Guidelines

When designing or cutting openings for cable trays, the following considerations are important: 1. Allowance for Installation and Fit The opening should be larger than the tray to ensure the tray can be easily positioned and secured without interference from surrounding structures. A typical practice is to add 2–4 inches (50–100 mm) to the width and height of the tray to allow for proper alignment and handling during installation.

2. Thermal Expansion and Contraction Cable trays, especially metal ones, expand and contract with temperature changes. Providing extra space in the reserved opening prevents stress on the tray and cables, reducing the risk of deformation or damage.

3.

Cable Fill and Future Expansion NE

C Article 392 recommends that trays should not be filled beyond 50% of their capacity for power cables and may require additional space for large or mixed cable types. The reserved opening should therefore accommodate not only the tray but also potential future cable additions. 4.

Compliance with StandardsNEC 392: Ensures safe installation and proper support of cables, emphasizing that trays must have adequate space for cables and covers if needed.

IE

C 61537: Provides guidelines for tray sizing, fill, and spacing to maintain cable safety, thermal performance, and maintainability. 5. Practical Example For a cable tray that is 12 inches wide and 4 inches high, the reserved opening might be 16 inches wide and 8 inches high, providing 2 inches of clearance on each side and 4 inches for height if a cover or additional clearance is required.

Summary

To ensure proper installation, thermal safety, and future flexibility, the reserved opening for a cable tray should be slightly larger than the tray itself, typically 2–4 inches wider and taller than the tray dimensions. This approach aligns with NEC and IEC recommendations for safe and maintainable cable tray installations.