Which cable tray material or finish is best for indoor vs. outdoor installations?
Material selection should be based on environmental factors including exposure to moisture, chemicals, salt spray, UV light, and temperature swings.
For outdoor installations, stainless steel (304/316), industrial powder coated or hot dip galvanized (HDG) finish for corrosion resistance is recommended.
For interior installations, use pre-galvanized, galvanized, or powder coated finishes for protection and appearance.
How do I mount a cable tray on the ceiling, wall, under floors, or racks?
Select the appropriate support hardware for the application:
- Ceiling-mounted trays typically use threaded rods or trapeze hangers anchored to overhead structural elements.
- Wall-mounted trays rely on brackets or cleats attached to studs or solid vertical walls.
- Under-floor-mounted trays sit on pedestals or supports anchored to the floor.
- Rooftop trays use stanchions or ballast blocks designed for wind and weather exposure.
- Rack-mounted trays in data centers or telecom rooms attach directly to racks or overhead beams.
In all cases, supports must be properly spaced and the trays securely fastened, grounded and bonded while adhering to NEC requirements for cable separation and fill limits to ensure safe, code-compliant installations.
Which NEC-approved cable types can be loaded into a cable tray?
As per NEC Article 392, commonly approved cable types include power, control, communication and instrumentation (TC/PLTC/ITC/MC/MI/ CMP/CMR/CMG), fiber optic (OFC/OFN), and alarm cables (NPLF/FPL).
Power and data lines should be separated to prevent electromagnetic interference (EMI), maintain a specific bend radius to avoid damage, and follow proper support spacing to prevent sagging.
Cable types such as Romex (NM), Underground Feeder (UF), Service Entrance Cable (SE), THHN/THWN are not permitted in cable trays.
What are acceptable cable tray fill capacities?
As per NEC Article 392.22, cable tray fill is limited to 50% of its cross-sectional area for power and control cables, and 40% for multi-conductor communications, data, or fiber optic cables.
BICSI guidelines are similar, recommending a maximum fill of 40% to 50% for low voltage copper and fiber optic cables, and up to 40% for power cables.
These limits allow for proper airflow, bend radius, and future expansion. Modestly upsizing tray width and depth at initial install is usually less costly than retrofits/expansion.
How do I calculate tray fill and choose the right cable tray size?
For low voltage/communication cables the NEC-approved target fill ratio is 50% of the cross-sectional tray area. It is recommended to allow for 40% growth in cable volume at initial installation.
To determine the correct tray width and depth, identify the size and type of cables to be installed. Calculate the cross-sectional area of each type and multiply by the number of cables. (Remember to account for 40% growth in future cable volume). Next, determine the trays' usable cross-sectional area in square inches (WxD/2), and select a size that keeps the fill within the 50% NEC limit.
For medium and high voltage cables, multiple the outside cable diameter by the number of cables to calculate tray size. Reduce fill by 30% to 40% to allow for heat dissipation. Derate ampacity according to NEC 310.15 for bundling and ambient temperature.
Can I mount accessories or devices directly to the tray?
Yes. Drop-outs, patch panels, utility boxes, cameras, and power modules can be affixed to the cable tray using compatible brackets or integrated rails. Be sure to verify tray and accessory load ratings, maintain cable bend radius at exit points, and preserve bonding continuity across fittings.
Do trays need bonding or grounding?
Yes, all metallic cable trays must be bonded to maintain electrical continuity and provide a fault path as per NEC Article 392. If the tray is to be used as an EGC (Equipment Ground Conductor) it must be UL Classified for that purpose and meet NEC 392 requirements for cross sectional area and maintain its full electrical continuity.
If the tray is non-metallic, i.e. fiberglass, it cannot serve as an EGC and will require an additional ground conductor. Bond all sections, ensure coatings do not interrupt continuity at joints, add bonding jumpers where required, and verify continuity after installation.
How can I reduce material storage, handling, and freight on the job site?
Use nested, lightweight, modular tray sections and sequence deliveries by area or floor. Nesting cuts warehousing space, carbon footprint, elevator lifts and trucking expenses. Lighter sections reduce installer handling time and fatigue.
How do I minimize on-site fabrication and labor?
On-site custom-fabricated directional changes increase labor, slow installation, and inflate costs. Two options here depending on load:
- Rigid wire basket tray systems with prefabricated Tees, turns, crosses, drop-outs, and quick-connect splices.
- Hand-bendable cable trays reduce the need for special fittings and navigate around obstacles without tools.
Always standardize and specify support locations in drawings to streamline installation.
What are best practices for integrating cable pathways with raised access floors or rooftop solar arrays?
Choose systems with universal brackets and adapter plates listed for the application. Maintain roof membrane integrity using non-penetrating supports, confirm NEMA/UL/CSA compatibility, and coordinate with structural/electrical drawings.
When should I choose a wire basket over a ladder tray?
Each serves different needs.
- Wire basket trays are more affordable, flexible, easy to install and accessorize, and are ideal for data and low-voltage cable runs with multiple directional and elevation changes.
- Ladder trays feature side rails connected to rungs and provide strong support and excellent ventilation for heavy-duty applications like high voltage power cables, but they are heavier, less flexible, and costly.
