Okonite wire and cable - methods for determining conduit sizes
Installation Practices
Determining Conduit Sizes

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Conduits or ducts should be properly constructed having smooth walls and of adequate size as determined by the overall cable diameter and recommended percentage of fill of conduit area.
.

Dimensions
of conduit

Nominal size
conduit inches

Internal diameter
inches

Area
square inches

   .... 1
    ....1 1/4
   .... 1 1/2
    ....2

1.049
1.380
1.610
2.067

0.86.......
1.50
.......
2.04
.......
3.36
.......

    ....2 1/2
   
....3
   
....3 1/2
   
....4

2.469
3.068
3.548
4.026

4.79.......
7.38
.......
9.90
.......
12.72
.......

    ....5
   
....6

5.047
6.065

20.00.......
28.89
.......


For groups or combinations of cables it is recommended that the conduit or tubing be of such size that the sum of the cross-sectional areas of the individual cables will not be more than the percentage of the interior cross-sectional area of the conduit or tubing as shown in the following tables.

Maximum percent internal
area of conduit or tubing

Number of cables

 

1

2

3

4

Over 4

Cables
(not lead-covered)

53

31

40

40

40

Lead-covered
cables

55

30

40

38

35

....

Maximum percent internal
diameter of conduit or tubing

Number of cables

 

1

2

3

4

Cables
(not lead-covered)

72.8

39.3

36.5

31.6

Lead-covered
cables

74.2

38.7

36.5

30.8



Maximum allowable diameter
(in inches) of individual cables
in given size of conduit

Non-metallic jacketed cable —
all cables of same outside diameter

Nominal
size
conduit

Number of cables having same O.D.

1

2*

3*

4*

    ..1/2
   
..3/4
  ..1
 
..1 1/4

0.453
0.600
0.763
1.010

0.244
0.324
0.412
0.542

0.227
0.301
0.383
0.504

0.197
0.260
0.332
0.436

  ..1 1/2
 
..2
 
..2 1/2
 
..3

1.173
1.505
1.797
2.234

0.633
0.812
0.970
1.206

0.588
0.754
0.901
1.120

0.509
0.653
0.780
0.970

  ..3 1/2
 
..4
 
..5
 
..6

2.583
2.930
3.675
4.416

1.395
1.583
1.985
2.385

1.296
1.470
1.844
2.215

1.121
1.273
1.595
1.916


NOTE: To determine the size conduit required for any number (n) of equal diameter cables in excess of four, multiply the diameter of one cable bysquare root (n  4).

This will give the “equivalent” diameter of four such cables and the conduit size required for (n) cables may then be found by using the column for four cables.

* These diameters are based on percent fill only. The Jam Ratio, Conduit OD to Cable ID, should be checked to avoid possible jamming.

 


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However, information is subject to change. Not responsible for typographical errors.

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Ramsey, New Jersey 07446
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