Yao Yao University of Virginia
12/6/07
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.
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
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
CM10 - (.1200) / Table 2Tray Size
50% fill ratio / Fill 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
* 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
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 capacity
2 AWG / 10 AWG / 22AWG / Total Weight/Length6 / 6 / 12 / 4.924 lbs/ft / 7.327kgs/m
5 / 5 / 10 / 4.187 lbs/ft / 6.230 kgs/m
4 / 4 / 8 / 3.283 lbs/ ft / 4.885 kgs/m
3 / 3 / 6 / 2.462 lbs/ft / 3.664 kgs/m
2 / 2 / 4 / 1.641 lbs/ft / 2.443 kgs/m
1 / 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.
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 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 Length6 / 6 / 12 / 4.924 lbs/ft / 7.327kgs/m / 3.75 ft / 1.14 m
5 / 5 / 10 / 4.187 lbs/ft / 6.230 kgs/m / 4.25 ft / 1.30 m
4 / 4 / 8 / 3.283 lbs/ ft / 4.885 kgs/m / 5.13 ft / 1.56 m
3 / 3 / 6 / 2.462 lbs/ft / 3.664 kgs/m / 6.43 ft / 1.96 m
2 / 2 / 4 / 1.641 lbs/ft / 2.443 kgs/m / 8.83 ft / 2.69 m
1 / 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.
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 Length6 / 6 / 12 / 4.924 lbs/ft / 7.327kgs/m / 3.99 ft / 1.22 m
5 / 5 / 10 / 4.187 lbs/ft / 6.230 kgs/m / 4.39 ft / 1.34 m
4 / 4 / 8 / 3.283 lbs/ ft / 4.885 kgs/m / 5.11 ft / 1.56 m
3 / 3 / 6 / 2.462 lbs/ft / 3.664 kgs/m / 6.21 ft / 1.89 m
2 / 2 / 4 / 1.641 lbs/ft / 2.443 kgs/m / 8.57 ft / 2.61 m
1 / 1 / 2 / 0.821 lbs/ft / 1.221 kgs/m / 27.57 ft / 8.41 m
Conversion used:
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
2 AWG / 10 AWG / 22AWG / Total Weight/Length / Cable Tray Support Length3 / 3 / 6 / 2.462 lbs/ft / 3.664 kgs/m / 7.52 ft / 2.29 m
2 / 2 / 4 / 1.641 lbs/ft / 2.443 kgs/m / 9.50 ft / 2.90 m
1 / 1 / 2 / 0.821 lbs/ft / 1.221 kgs/m / 14.15 ft / 4.31 m
The cable tray support configurations are calculated below.
Table 6: Cable tray support length for 2” x 2” x 10” tray
Conversion used:
Using power regression, the graph is shown below.
Graph 4: Relationship between density and length 2” x 2” x 10” tray
2 AWG / 10 AWG / 22AWG / Total Weight/Length / Cable Tray Support Length3 / 3 / 6 / 2.462 lbs/ft / 3.664 kgs/m / 7.40 ft / 2.26 m
2 / 2 / 4 / 1.641 lbs/ft / 2.443 kgs/m / 9.45 ft / 2.88 m
1 / 1 / 2 / 0.821 lbs/ft / 1.221 kgs/m / 15.47 ft / 4.71 m
The cable tray support configurations are calculated below.
Table 7: Cable tray support length for 2” x 2” x 10” tray
Conversion used:
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