Vertical bends in trapezoidal cable trays allow smooth directional changes in the vertical plane while maintaining cable integrity and proper support.

Overview

Vertical bends are used to change the elevation of a cable tray, such as moving from a horizontal run to a higher or lower level along walls, ceilings, or equipment racks . They are available in inside and outside bend configurations and can be fabricated for any angle as required by the installation layout . These bends are compatible with perforated, ladder, and wire mesh cable trays and can be customized to match the tray width and depth .

Bend Radius Considerations

The bend radius is critical to prevent cable damage. The minimum radius of a vertical bend must be equal to or greater than the minimum bending radius of the largest cable in the tray . The general formula for calculating the minimum bend radius is: R = K × D Where:

• R = minimum bend radius
• D = cable outside diameter
• K = bending factor (typically 8–12 for control, multicore, or single-core power cables) Standard tray bend radii are commonly 300 mm, 450 mm, 600 mm, and 900 mm, and installers should select the next higher standard radius to ensure safe cable installation . Field-fabricated bends can be made by cutting and bolting tray sections, but care must be taken to maintain a smooth curve to avoid sharp angles that could damage cables .

Installation Tips

• Secure the tray to walls, ceilings, or supports before bending to maintain alignment .
• Use pre-fabricated bends when possible to ensure consistent radius and reduce installation time .
• Mark side rails at intervals based on the calculated arc length if fabricating bends on-site .
• Check cable compatibility: Ensure the bend radius accommodates all cables in the tray, especially larger diameter or high-voltage cables .

Standards and Guidelines

While the NEC (National Electrical Code) allows field bends of cable trays (NEC 392.18(A)), there is no strict minimum radius specified; the manufacturer's recommendations and cable bend limits govern the design . For metallic trays, NEMA VE-1 provides guidance on bend fabrication and radius selection.

Summary

Vertical bends in trapezoidal cable trays are essential for routing cables in the vertical plane. Proper radius selection, alignment, and support are crucial to maintain cable integrity and comply with installation standards. Using pre-fabricated bends or carefully fabricated field bends ensures safe and efficient cable management .