Cable Tray Fill Calculator

Our cable tray fill calculator is designers to compute the appropriate size and capacity of cable trays.

You need to install 50 power cables, each with a diameter of 0.5 inches, in a 4-inch deep cable tray. The calculator would help determine if the chosen tray is sufficient or if a larger size is needed.

Cable Tray Fill Calculator

Tray Size (W x D)	Cable Diameter	Number of Cables	Total Cable Area	Allowable Fill Area	Fill Ratio
12″ x 4″	0.5″	40	7.85 in²	19.2 in²	40.89%
18″ x 6″	0.75″	50	22.09 in²	43.2 in²	51.13%
24″ x 4″	0.4″	100	12.57 in²	38.4 in²	32.73%
36″ x 6″	1.0″	60	47.12 in²	86.4 in²	54.54%
30″ x 5″	0.6″	80	18.85 in²	60 in²	31.42%
48″ x 8″	1.25″	40	39.27 in²	153.6 in²	25.59%
24″ x 8″	0.75″	70	27.36 in²	76.8 in²	35.56%
12″ x 3″	0.5″	30	11.78 in²	14.4 in²	81.67%
60″ x 10″	1.5″	20	47.12 in²	240 in²	19.63%
18″ x 4″	0.4″	50	10.05 in²	28.8 in²	34.88%
36″ x 4″	0.75″	90	42.39 in²	86.4 in²	49.05%
30″ x 6″	1.0″	50	39.27 in²	72 in²	54.52%
48″ x 6″	0.5″	80	19.63 in²	115.2 in²	17.04%

Cable Tray Fill Calculation Formula

The fundamental formula for calculating cable tray fill is:

Fill Area = Sum of Cable Cross-Sectional Areas / Allowable Fill Area

• Cable Cross-Sectional Area: For round cables, use πr², where r is the cable radius.
• Allowable Fill Area: This varies based on the tray type and local electrical codes.

Calculate the total cross-sectional area of all cables:

Total Cable Area = Σ (π * r² * n) 

Where:

• r = radius of each cable type
• n = number of cables of each type

Determine the allowable fill area based on tray dimensions and fill requirements:

Allowable Fill Area = Tray Width * Maximum Fill Depth * Fill Factor

Calculate the fill ratio: Fill Ratio = Total Cable Area / Allowable Fill Area

Let’s say you have a 24-inch wide, 4-inch deep tray with a 40% fill requirement.

You need to install 30 cables with a 0.5-inch diameter and 20 cables with a 0.75-inch diameter.

• Total Cable Area = (π 0.25² 30) + (π 0.375² 20) = 13.74 in²
• Allowable Fill Area = 24 4 0.40 = 38.4 in²
• Fill Ratio = 13.74 / 38.4 = 0.36 or 36%

In this case, the cable tray has sufficient capacity.

How to Calculate Cable Tray Filling Ratio

To calculate it:

Determine the total cross-sectional area of all cables (as shown above).

Calculate the tray’s internal cross-sectional area.

Divide the cable area by the tray area and multiply by 100 for a percentage.

Filling Ratio (%) = (Total Cable Area / Tray Internal Area) * 100

Consider a 6-inch wide, 4-inch deep cable tray containing 40 cables, each with a diameter of 0.4 inches.

• Total Cable Area = π (0.2)² 40 = 5.03 in²
• Tray Internal Area = 6 * 4 = 24 in²
• Filling Ratio = (5.03 / 24) * 100 = 20.95%

This filling ratio is well within typical limits, leaving room for future expansion.

What is the Fill Capacity of a Cable Tray?

• Ladder trays: 40-50% for power cables, up to 60% for control/instrumentation
• Solid bottom trays: 30-40% for power cables, up to 50% for control/instrumentation

The fill capacity of a cable tray refers to the maximum amount of space that can be occupied by cables while maintaining proper ventilation and accessibility, typically expressed as a percentage of the tray’s cross-sectional area.

Fill capacity limits vary depending on:

• Tray type (ladder, solid bottom, etc.)
• Cable types (power, control, mixed)
• Local electrical codes

A 12-inch wide, 3-inch deep ladder tray for power cables:

Maximum Fill Capacity = Tray Width * Tray Depth * Fill Factor
Maximum Fill Capacity = 12 * 3 * 0.4 = 14.4 in²

This tray can accommodate up to 14.4 square inches of cable cross-sectional area.

What is the NEC Code for Cable Tray Fill?

• Single conductor cables 4/0 AWG and larger: Fill up to 60% of the tray cross-sectional area
• Multiconductor cables: Fill up to 50% (40% if ≥4 inches in diameter)
• Solid bottom trays: Multiconductor cables must not exceed a depth equivalent to the tray sidewall height

The National Electrical Code (NEC) provides specific guidelines for cable tray fill in Article 392.

For an 18-inch wide, 5-inch deep tray with multiconductor cables:

Maximum Fill Area = Tray Width * Tray Depth * Allowable Percentage
Maximum Fill Area = 18 * 5 * 0.5 = 45 in²

The NEC would allow up to 45 square inches of cable cross-sectional area in this tray.

How to Calculate the Load Capacity of a Cable Tray?

Determine the total weight of all cables:

Total Cable Weight = Σ (Cable Weight per Foot * Number of Cables * Tray Length)

Add any additional loads (e.g., splice boxes, future expansion).

Compare the total load to the tray’s specified load rating.

A 50-foot tray containing 30 cables weighing 0.5 lbs/ft each:

• Total Cable Weight = 0.5 * 30 * 50 = 750 lbs
• Add 10% for future expansion: Total Weight with Expansion = 750 * 1.1 = 825 lbs
• If the tray’s load rating is 100 lbs/ft, its capacity is Capacity = 50 * 100 = 5000 lbs.

In this case, the load (825 lbs) is well within the tray’s capacity (5000 lbs).

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