The crossarm of a cable tray is generally slightly wider than the tray itself, typically extending 1–3 inches beyond each side to provide structural support and clearance.

Standard Practice

In cable tray installations, crossarms are designed to support the tray and its cable load while allowing for proper installation and maintenance. The crossarm width is usually wider than the tray's nominal width to ensure stability and accommodate mounting hardware, brackets, or fasteners . This overhang also helps prevent the tray from tipping or shifting under load.

Typical Dimensions

• For a ladder or ventilated tray, the crossarm may extend 1–3 inches (25–75 mm) beyond each side of the tray, depending on the tray width and load requirements .
• Wider trays (e.g., 36–48 inches) often require proportionally wider crossarms to maintain structural integrity.
• The exact overhang can vary by manufacturer and project specifications, but the principle is to ensure the tray is fully supported along its edges without interfering with cable routing or adjacent structures .

Engineering Considerations

• Load capacity: The crossarm must support the tray's weight plus the cable load, so a slightly wider crossarm distributes the load more effectively.
• Clearance: The overhang allows for cable bending, installation of covers, and compliance with NEC or IEC spacing requirements .
• Compatibility: Crossarms are standardized to match common tray widths, ensuring that trays, fittings, and supports remain compatible across different installations .

Summary

While the exact width difference depends on the tray type and manufacturer, crossarms are almost always wider than the cable tray itself, typically by 1–3 inches per side, to provide proper support, maintain stability, and allow for safe cable installation and maintenance . This ensures compliance with structural and electrical standards while facilitating future expansion.