How should the quota be applied to cable tray supports

Cable tray supports should be spaced according to the tray type, load, and installation standards, typically ranging from 1.5 to 3 meters, following IEC 61537 or equivalent national standards.

Support Spacing Guidelines

The spacing of cable tray supports, often referred to as the "quota," depends on several factors including the type of tray, material, load of cables, and environmental conditions. For standard installations:

• Straight steel or aluminum trays: Support spacing is commonly 2 to 3 meters for light to medium loads, while heavier loads may require closer spacing around 1.5 meters .
• Mesh or ventilated trays: These may require shorter support intervals due to reduced structural rigidity .
• Elbows, tees, and bends: Special consideration is needed as loads are uneven; supports should be placed closer to these points to maintain stability .

Calculation Method

A practical formula to determine the number of supports is: Support Quantity = Total Tray Length ÷ Support Spacing + 1 For example, a 20-meter tray with 2-meter spacing requires: 20 ÷ 2 + 1 = 11 supports, including both ends .

Standards and Compliance

• IEC 61537: Provides international guidelines for cable tray systems, including mechanical strength, corrosion resistance, and support requirements .
• BS EN 61537: The British standard equivalent, ensuring safe installation and load-bearing capacity .
• Supports must be mechanically capable of handling the cable load and environmental factors, including potential short-circuit forces .

Practical Recommendations

• Always select supports compatible with the tray system to ensure stability and safety .
• Consider environmental conditions such as humidity, temperature, and chemical exposure, which may affect material choice and spacing .
• For instrumentation or control cables, closer rung spacing (150–230 mm) may be preferable to protect smaller cables . By following these guidelines, engineers and installers can ensure that cable trays are secure, compliant, and capable of supporting the intended cable load safely.