Selection Methods for Low-Voltage Cable Trays in Vertical Shafts

Ladder or ventilated trough cable trays are generally preferred for low-voltage installations in vertical shafts due to their superior ventilation, load support, and compliance with NEC standards.

Cable Tray Type Selection

For low-voltage systems in vertical shafts, ladder trays are the predominant choice, used in approximately 75% of installations, because they allow maximum airflow, which helps dissipate heat from conductors and prevents insulation degradation. Ventilated trough trays are also suitable, especially for single-conductor or Type MV cables, as they provide structural support while allowing some airflow. Solid-bottom trays are generally avoided in vertical shafts for low-voltage cables, particularly in dust-prone or hazardous locations, due to limited ventilation and heat dissipation.

Material and Corrosion Considerations

Cable trays can be fabricated from steel, aluminum, stainless steel, or pultruded fiberglass, with material selection based on environmental conditions. For vertical shafts, galvanized steel or stainless steel is often preferred for corrosion resistance and mechanical strength, especially in humid or industrial environments. Aluminum offers excellent corrosion resistance and a favorable strength-to-weight ratio, while fiberglass trays provide chemical resistance and lightweight installation options.

Sizing and Load Capacity

Tray width and load rating must accommodate the number, type, and weight of cables, including future expansion. Ampacity derating must be considered for vertical installations, as heat dissipation is affected by cable density and orientation.

NE

C Sections 392. 9–392. 12 provide guidelines for tray fill, cable spacing, and ampacity, ensuring that conductors do not exceed their maximum operating temperature.

Adding extra width (e.g., six inches) can increase cost but improves flexibility for future cable additions.

Supports and Installation

Vertical shafts require strong hangers or brackets at consistent intervals to prevent tray sagging or failure. Edge-wise or non-horizontal orientations are permissible if manufacturer guidelines are followed, which can reduce dust accumulation in vertical shafts. Proper anchoring of single-conductor cables is critical to prevent displacement under fault conditions.

Cable Separation and SafetyLow-voltage cables should be separated from high-voltage or power cables using separate trays or solid barriers to prevent interference and maintain safety. Ladder tray rungs provide convenient tie-down points to secure cables and maintain proper spacing, which is especially important in vertical runs.

Summary

When selecting low-voltage cable trays for vertical shafts: Prefer ladder or ventilated trough trays for airflow and heat dissipation. Choose materials based on environmental conditions (galvanized steel, stainless steel, aluminum, or fiberglass). Ensure tray sizing and load rating accommodate current and future cable loads.

Install strong, consistent supports and secure cables to prevent displacement. Maintain separation from high-voltage cables and follow NEC fill and ampacity guidelines. These principles ensure safe, reliable, and code-compliant installations in vertical shaft environments.