Substation cable trays must be sized to accommodate cable diameters, maintain proper separation between power and signal cables, and support heavy loads with appropriate spans and dividers.

Cable Tray Width and Fill

The width of the cable tray should be sufficient to hold all cables without exceeding recommended fill ratios. For ladder trays, the interior usable width must at least equal the sum of the diameters of all cables installed in layers. For solid-bottom trays, the total cable diameter should not exceed 90% of the tray width. When mixing large power cables (4/0 AWG or larger) with smaller cables, it is recommended to divide the tray into separate zones to prevent interference and maintain neat installation .

Rung Spacing and Tray Type

• Ladder trays are commonly used for heavy power cables and are available in widths from 6 to 48 inches, with rung spacings of 6, 9, 12, or 18 inches. Wider trays and wider rung spacing reduce overall strength, so care must be taken to select rungs that can safely bear the load .
• For small-diameter control and instrumentation cables, 6–12 inch rung spacing is preferred to prevent drooping and maintain neatness .
• Solid or ventilated trays may be used for signal or instrumentation cables, especially where electromagnetic interference is a concern .

Support Spacing

• Supports should be placed every 1.5 to 2 meters for heavy power cables to prevent sagging .
• Additional supports are recommended within 600 mm of corners, T-junctions, or bends to maintain structural integrity .
• For long runs, expansion gaps every 30–40 meters accommodate thermal expansion and contraction of metal trays in outdoor substations .

Separation of Cable Types

• Maintain a vertical gap of at least 300 mm between power and signal/data trays to prevent electromagnetic interference .
• Use solid metal dividers when power and signal cables must share a tray to block magnetic fields and ensure reliable operation of sensitive equipment .

Compliance and Standards

• Follow IEC 61537 for mechanical strength, corrosion resistance, electrical continuity, fire resistance, ventilation, and fill ratio requirements .
• Adhere to NEC guidelines for cable ampacity, tray fill, and separation of large and small cables .
• Ensure that cable bending radii recommended by the manufacturer are not violated when routing cables into or out of trays .

Practical Recommendations

• Select tray width based on total cable diameters and layer configuration.
• Use ladder trays for heavy power cables and solid or ventilated trays for signal cables.
• Plan support intervals and expansion gaps to maintain long-term stability.
• Separate power and signal cables with dividers or vertical spacing to prevent interference.
• Verify compliance with IEC and NEC standards for safety and performance. By following these guidelines, substation cable trays will safely support heavy power cables, maintain signal integrity, and comply with international and national standards.