How should cable trays be placed in the vertical shaft of the low-voltage electrical shaft

Vertical cable trays in low-voltage shafts must be securely mounted, properly supported, and organized to comply with NEC standards and ensure safe, accessible cable routing.

Planning and Tray Selection

Before installation, plan the tray route carefully, considering shaft dimensions, cable fill, and separation requirements for low-voltage cables. Choose a tray type suitable for vertical runs, such as ladder or ventilated trough trays. Ladder trays are ideal for larger low-voltage bundles because their rungs provide convenient anchor points for cable ties and allow airflow to prevent heat buildup.

For environments with moisture or corrosive conditions, consider fiberglass-reinforced plastic (FRP) trays for non-conductive, corrosion-resistant support.

Mounting and Support

Secure the tray to the shaft walls using brackets or clamps rated for vertical loads. Support spacing should follow NEC guidelines, typically 1. 5 to 3 meters (5–10 feet) depending on tray type and cable weight.

For vertical runs, fasten cables to the tray rungs or transverse members to prevent sagging and maintain spacing. Ensure at least 12 inches of vertical clearance above the tray for installation and maintenance access, as required by the 2026 NEC update.

Cable Installation and Management

Use Tray Rated (Type TC) or Metal-Clad (Type MC) cables suitable for open-air tray environments. Maintain separation between high-power and low-voltage cables to prevent electromagnetic interference (EMI). Do not exceed fill limits: 50% for control/low-voltage cables.

Use listed cable ties approved for tray applications; avoid standard plastic ties that may fail in plenum or high-temperature conditions. At transition points, provide strain relief to protect terminations and avoid overtightening ties to prevent cable jacket damage.

Grounding and Safety

If using metallic trays, ensure proper bonding and grounding according to NEC requirements; the tray can serve as an equipment grounding conductor if compliant. Avoid installing trays in hoistways or fully enclosed spaces; they must remain accessible for inspection and maintenance.

Additional Tips

For long vertical runs, consider intermediate supports to prevent undue mechanical stress on cables. Ensure rung spacing is appropriate (typically 6–9 inches) to support low-voltage cables without sagging. Plan for future maintenance by leaving adequate space for cable addition or replacement.

Following these steps ensures a safe, code-compliant, and durable vertical cable tray installation in low-voltage electrical shafts, minimizing risks of overheating, mechanical damage, and EMI interference.