Yao Yao University of Virginia12/6/07

Specifications for Cable Trays

Introduction:

The power cables are placed inside cable trays. To do this the tray must be able to support the

density (in weight/length) of the cables. There are 6 different combination of cables placed

inside the cable tray. To make sure that the cable trays will not collapse, the load capacity

(how often the cable tray needs to be supported) for each of the 6 configurations needs to be

determined.

This document specifies the mass of each cable per length, the total mass of the cables in the

tray, and the load capacity of the cable tray.

Design Specification:

Three different cables are placed inside the 4”x2” tray. The cables are 2 conductor 2AWG

(from Aetna), 10 AWG (from Belden), and 22AWG (from Belden). Figure 1 below shows how

the cables are placed inside the trays. In this configuration, there are 6 2AWG, 6 10AWG, and

12 22AWG cables. This is the maximum amount of cables placed inside the tray. In the 5 other

configurations, the cable amounts are decreased. The details are shown in the calculation

section.

Fig. 1: Cross section of the cable tray.

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Table 1: Specifications of Cable’s Weight/Length

Aetna TC, 2AWG 2c 715 lbs/1000ft (0.715 lb/ft)

Belden 10 AWG, 2c 83 lbs/1000ft (0.0831 lb/ft)

Belden 22 AWG, 2c 11.3 lbs/1000ft (0.0113 lb/ft)

The data

above following data were edited and taken from their source in Fig. 2 below (http://www.belden.com and http://www.aetnawire.com ).

Fig. 2: Source of cables

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Yao Yao University of Virginia12/6/07

Specification of the CM10 4” x 2” x 10” and CM10 2” x 2” x 10” tray

The cable tray is a wire frame tray from Cableorganizer.com. From the table given by its

website, it is recommended that a 2” x 4” x 10” tray could hold a maximum of 2.8338 lbs/ft

based on category 6 UTP cables. It can hold a maximum of 17 lbs/ft for 5 feet and 14 lbs/ft for

10 feet based on tested load. A 2” x 2” x 10” tray could hold a maximum of 1.452 lbs/ft based

on category 6 UTP cables. It can hold a maximum of 25 lbs/ft for 5 feet and 14 lbs/ft for 10 feet

based on tested load. These are the only official data given.

Table 2: Load capacity information taken from CableOrganizer.com

* Chart is based on 50% fill of 4 UTP Category 6 cable (O.D.=.21 .033lbs/ft)** Not maximum loading weight for the tray; practical guide on the amount of cable weight that can be installed*** Tested in accordance with NEMA VE-1/CSA E222.2 #126.1

CM10 - (.1200) Table 2Tray Size

50% fill ratioFill Area

Max. # Cables*

Approx. Max. Cable Weight** (lbs/ft)

Tested Load Capacity*** (lbs/ft)5' 10'

(2x2x10) 4.4 44 1.452 25 15(2x4x10) 8.8 86 2.838 17 14(2x6x10) 13.2 130 4.29 20 10(2x8x10) 17.6 174 5.742 25 12(2x12x10) 26.4 260 8.58 31 16(4x2x10) 8.4 84 2.772 25 13(4x4x10) 25.2 252 5.544 27 15(4x6x10) 33.6 336 11.088 41 20(4x8x10) 50.4 504 16.362 55 31(4x12x10) 12.4 124 4.092 33 16

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Calculations:

This table specifies the mass/length for 6 different combinations of each cable in the tray,

using the weight/length table of the cables. The 2” x 4” x 10” tray holds all the combinations of

cables. The 2” x 2” x 10” holds the last three combinations starting from three 2 AWG, three 10

AWG, and six 22 AWG cables.

Table 3: Cable load capacity2 AWG 10 AWG 22AWG Total Weight/Length6 6 12 4.924 lbs/ft 7.327kgs/m5 5 10 4.187 lbs/ft 6.230 kgs/m4 4 8 3.283 lbs/ ft 4.885 kgs/m3 3 6 2.462 lbs/ft 3.664 kgs/m2 2 4 1.641 lbs/ft 2.443 kgs/m1 1 2 0.821 lbs/ft 1.221 kgs/m

Conversion used:

According to the test loaded capacity of 2” x 4” x 10” tray, it can hold 17 pounds of cables in 5

feet. This would give about 3.4 lbs/ft if the tray was 5 ft long with end support. This is a lot less

than the required load for the cables, which is at 4.924 lbs/ft. This implies that the cable

support must be less than 5 feet to support the heaviest configuration.

For 2” x 2” x 10” tray, it can hold 25 lbs/ft for 5 feet. This implies 5lbs/ft, but since its maximum

cable weight is at 2.462 lbs/ft, the support length would be greater than 5 feet.

Using static physics, the general relationship between the weight and the length of cable

support can be shown.

Moment of bending for a simple end support shown in Figure 2 is

for a uniformly distributed linear weight density of w, length l, and moment of bending M.

Fig. 3: Cross section of tray with end support and length l.

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Weight/Length vs. Lengthy = 26.683x-1.2801

0

1

2

3

4

5

6

0 2 4 6 8 10 12 14

Length(feet)

Wei

ght/L

engt

h(lb

s/ft)

Yao Yao University of Virginia12/6/07

So the density (weight/length) is proportional to length in formula .

There are 2 different ways to do regression for , which are:

These two regressions’ calculations are done for each tray.

2” x 4” x 10” tray

There are two data points for 5 and 10 feet cable trays. The 5 feet tray holds 3.4 lbs/ft and 10

feet tray holds 1.4 lbs/ft. Using power regression , the two data points can be fitted,

shown in graph below.

Graph 1: Relationship between density and length of 2” x 4” x 10” tray

At least 5 lbs/ft is to be supported for

the heaviest configuration. From the graph and equation, when y = 4.924, x = 3.77. This

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means that 3.77 feet of cable tray with end supports holds about 5 lbs/ft according to this

regression formula. The cable tray support lengths for the other 5 configuration are calculated

below.

Table 4: Cable tray support length for 2” x 4” x 10” tray

2 AWG 10 AWG 22AWG Total Weight/Length Cable Tray Support Length

6 6 12 4.924 lbs/ft 7.327kgs/m 3.75 ft 1.14 m5 5 10 4.187 lbs/ft 6.230 kgs/m 4.25 ft 1.30 m4 4 8 3.283 lbs/ ft 4.885 kgs/m 5.13 ft 1.56 m3 3 6 2.462 lbs/ft 3.664 kgs/m 6.43 ft 1.96 m2 2 4 1.641 lbs/ft 2.443 kgs/m 8.83 ft 2.69 m1 1 2 0.821 lbs/ft 1.221 kgs/m 15.17 ft 4.62 m

Conversion used:

Using the regression , where y is the weight/length and x is the length, the data points

can be fitted differently.

Substituting two sets of x and y into the above equation gives:

This becomes a unique system of equations.

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Graph 2: Relationship between density and length of 2” x 4” x 10” tray

At least 5 lbs/ft is to be supported for the heaviest configuration. From the graph and equation,

when y = 4.924, x = 3.99. This means that 3.99 feet of cable tray with end supports holds

about 5 lbs/ft according to this formula. The cable tray support lengths for the configuration are

calculated below.

Table 5: Cable tray support length for 2” x 4” x 10” tray

2 AWG 10 AWG 22AWG Total Weight/Length Cable Tray Support Length

6 6 12 4.924 lbs/ft 7.327kgs/m 3.99 ft 1.22 m5 5 10 4.187 lbs/ft 6.230 kgs/m 4.39 ft 1.34 m4 4 8 3.283 lbs/ ft 4.885 kgs/m 5.11 ft 1.56 m3 3 6 2.462 lbs/ft 3.664 kgs/m 6.21 ft 1.89 m2 2 4 1.641 lbs/ft 2.443 kgs/m 8.57 ft 2.61 m1 1 2 0.821 lbs/ft 1.221 kgs/m 27.57 ft 8.41 m

Conversion used:

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Weight/Length vs. Length

y = 81.857x-1.737

0

1

2

3

4

5

6

7

8

9

10

0 2 4 6 8 10 12 14

Length(feet)

Wei

ght/L

engt

h(lb

s/ft)

Yao Yao University of Virginia12/6/07

2” x 2” x 10” tray

There are two data points for 5 and 10 feet cable trays. The 5 feet tray holds 5 lbs/ft and 10

feet tray holds 1.5 lbs/ft. Using power regression , the two data points can be fitted,

shown in graph below.

Graph 3: Relationship between density and length of 2” x 2” x 10” tray

The cable tray support configurations are calculated below.

Table 6: Cable tray support length for 2” x 2” x 10” tray

Conversion used:

2 AWG 10 AWG 22AWG Total Weight/Length Cable Tray Support Length

3 3 6 2.462 lbs/ft 3.664 kgs/m 7.52 ft 2.29 m2 2 4 1.641 lbs/ft 2.443 kgs/m 9.50 ft 2.90 m1 1 2 0.821 lbs/ft 1.221 kgs/m 14.15 ft 4.31 m

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Using power regression , the graph is shown below.

Graph 4: Relationship between density and length 2” x 2” x 10” tray

The cable tray support configurations are calculated below.

Table 7: Cable tray support length for 2” x 2” x 10” tray

Conversion used:

2 AWG 10 AWG 22AWG Total Weight/Length Cable Tray Support Length

3 3 6 2.462 lbs/ft 3.664 kgs/m 7.40 ft 2.26 m2 2 4 1.641 lbs/ft 2.443 kgs/m 9.45 ft 2.88 m1 1 2 0.821 lbs/ft 1.221 kgs/m 15.47 ft 4.71 m

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