The number of cable trays for elevator doors depends on the total number, size, and type of cables, as well as the allowable fill of each tray according to NEC guidelines.

Determining Cable Tray Requirements

Cable trays are used to support and route elevator cables safely from the machine room to the elevator doors, including power, control, and signal cables . The number of trays required is not fixed; it depends on:

• Cable quantity and size: Larger or more numerous cables may require multiple trays to avoid overfilling.
• Tray type: Ladder, ventilated, or solid-bottom trays have different fill capacities. Ventilated trays allow better airflow and higher fill percentages .
• Allowable fill: NEC Section 392 specifies that trays should generally not exceed 40–50% of their cross-sectional area to prevent overheating and mechanical stress .
• Future expansion: Designers often plan for additional trays to accommodate future cable additions without overloading existing trays .

Practical Guidelines for Elevator Doors

1. Separate trays for power and control cables: To reduce electromagnetic interference, it is common to route high-voltage power cables in one tray and low-voltage control or signal cables in another .
2. Tray sizing: Calculate the total cross-sectional area of all cables and select trays that maintain the recommended fill percentage. If the total cable area exceeds the capacity of a single tray, additional trays are required .
3. Short runs to doors: For the short horizontal or vertical runs from the hoistway to the elevator doors, a single tray may suffice if cable volume is low. For multiple doors or high-speed elevators with many signal and power lines, multiple trays may be necessary .
4. Compliance and safety: Ensure trays are properly supported, secured, and rated for the weight of the cables. Overloading trays can lead to mechanical failure or electrical hazards .

Summary

There is no universal number of cable trays for elevator doors. Typically, one tray per cable type (power vs. control) is used for a single door, but multiple trays may be required for:

• Multiple doors on the same floor
• High-speed or high-capacity elevators
• Future expansion needs The best approach is to calculate the total cable area, select trays according to NEC fill guidelines, and plan for separate trays for different cable types to ensure safety, compliance, and ease of maintenance .