Cable Tray Fill and Load Calculation

Qui ck Tray Quick Tray Fill and Load Calculations he folllowing tables and formulas are provided to help determine how many cables can be safely carried by  T he each size wire mesh cable tray tray and to determine the appropriate distance between supports for the load, based on number of cables, cable tray tray size, and bracket bracket type. Use the following formula to calculate the number of  cables that will result in a particular fill ratio, where:

 Wire Mesh Cable Tray Fill Ratio Fill ratio = Cross section of cable Cross section of tray

A = Inside Inside tra trayy area, area, in in.2 D = Cable diamet diameter er,, in inches inches

According to NEC 392.9 (B), when using ventilated tray tray with multiconductor control control cable, the sum of the crosssectional areas shall not exceed 50 percent of the interior cross section of the tray.

F = Fill Fill rat ratio io in in %

The Quick Tray Tray Wire Mesh Cable Tray Tray Fill Fi ll Table Table below shows the number of cables and the load in lbf/lineal foot developed by typical 4 pair and 6 pair cable weighing 20 lb/kft and 40 lb/kft, respectively respectively.. While this table is a useful guide, actual loads must be calculated using the cable specified.

N=

N = Number Number of cables The formula is F ( 100 ) * ( [(D/2)A2 * ]) Π

EXAMPLE: The installation will use CAT CAT cable at .19 in. diameter diameter,, 20 lb 2 per 1000 ft .The desired fill ratio is 40%.The wire mesh cable tray tray tray is 2 in. (51mm) high by by 2 in. (51mm) wide. A = 3.5 in. 2 D = .19 in. F = 40% N=

(

40 100

3.5 ) * ([(.19/2) 2 * ])

= 49 cables

Π

Load/foot = 49 cables * 20 lb = 0.98 lb/ft 1000 ft.

Quick Tray Tray Wire Mesh Cable Tray Tray Fill Fi ll Table at 50% Fill Catalog Number

Height in.

Width in.

Area in.2

CAT Cab Type (4 pai airr),.1 ),.19 9 in in. di diam ame ete terr, 20 lb lb//kf kftt No. Cables Load at 50% Fill lbf/lineal ft

CAT Ca Cab b Typ Type e (6 (6 pai pair) r),, .2 .26 6 iin.di n.diam ame ete terr, 40 lb/ lb/kf kftt No. Cables Load at 50% Fill lbf/lineal ft

QT2X2

2

1.75

3.5

62

1.24

32

1.28

QT2X4

2

3.75

7.5

133

2.66

70

2.8

QT2X6

2

5.5

11

195

3.9

10 3

4.12

QT2X8

2

7.5

15

266

5.32

1 41

5.64

QT2X12

2

11.5

23

408 40

8.16

216

8.64

QT2X16

2

15.5

31

550

11

29 1

11.64

QT2X18

2

17.5

35

6 21 62

12.42

329

13.16

QT2X20

2

19.5

39

6 92 69

13.84

367

14.68

QT2X24

2

23.5

47

8 34 83

16.68

442

17.68

QT4X4

4

3.75

15

266 26

5.32

141

5.64

QT4X8

4

7.5

30

5 32 53

10.64

282

11.28

QT4X12

4

11.5

46

8 16 81

16.32

433

17.32

QT4X16

4

15.5

62

1100 11

22

5 83

23.32

QT4X18

4

17.5

70

1242

24.84

65 9

26.36

QT4X20

4

19.5

78

1384

27.68

73 4

29.36

QT4X24

4

23.5

94

1668

33.36

88 5

35.4

16

Data subject to change without notice

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Quick Tray Fill and Load Calculations Supporting Quick Tray Wire Mesh Cable Tray The Quick Tray Wire Mesh Cable Tray is sized based on the number and type of cables required for the current and future need.A 50% fill ratio should equal the maximum number of cables pulled in a given cross section. Straight section supports installed at 5-foot (1.5m) centers are typical. For support spans greater than 5 feet (1.5m), cable loads must be evaluated to ensure that the span between the supports is suitable for the load.The support and Cable Tray Catalog Number

Maximum Load in lb/ft According to Span 5 ft 6 ft 7 ft 8 ft

9 ft

10 ft

QT2X2

17.17

12.54

7.51

6.04

4.77

3.86

QT2X4

18.10

14.00

11.30

9.30

7.40

5.10

QT2X6

25.10

19.80

16.00

13.40

11.00

9.00

QT2X8

25.10

19.80

16.00

13.40

11.00

9.00

QT2X12

36.00

27.70

22.10

18.10

14.60

10.50

QT2X18

65.00

45.50

33.80

26.10

19.40

15.00

QT2X20

65.00

45.50

33.80

26.10

19.40

15.00

QT2X24

67.00

48.70

37.80

30.30

23.70

17.00

QT4X8

43.80

35.90

30.10

25.40

21.20

17.00

QT4X12

57.95

43.77

27.77

22.94

18.12

14.68

QT4X20

89.80

71.00

57.70

47.60

38.50

22.00

QT4X24

89.80

71.00

57.70

47.60

38.50

22.00

anchor must be evaluated separately. Supports should be placed within 24 in. (610mm) of a splice on straight sections, and the span between supports should not exceed the length of tray. Additional supports will be required around bends and when the cable tray level changes. The load ratings of the hardware that supports the Quick  Tray Wire Mesh Cable Tray must also be considered. Load ratings for some commonly used supports are shown in the Support Maximum Load table below. Once the load/foot has been determined, the weight on each support can be determined by multiplying the load/foot by the number of feet between supports. EXAMPLE: Weight of span = Load/foot * No. ft between supports Load/foot figure from the 2 x 2 in. cable tray with 40% fill ratio example: .98 lb/ft Weight of span = .98 * 5 = 4.9 lb Weight on support = weight of span / 2

Cross section- load versus span 100 90 QT2 x 2

80   s    d   n   u   o   p   n    i    d   a   o    L

QT2 x 4

70

QT2 x 6(8)

60

QT2 x 12

50

QT2 x 18(20)

40

QT2 x 24 QT4 x 8

30

QT4 x 12

20

QT4 x 20(24)

10 0 5 ft

6 ft

7 ft

8 ft

9 ft

10 ft

Distance between supports

Support Maximum Load Catalog Number

Description

Bracket Width in. mm

Max. Load lbs

QTCB4

C Bracket

4

102

259

QTCB8

C Bracket

8

203

216

QTCB12

C Bracket

12

305

108

QTLB4

L Bracket

4

102

259

QTLB8

L Bracket

8

203

216

QTLB12

L Bracket

12

305

108

QTTH

Trapeze Hanging Clips

–

–

216

Data subject to change without notice

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