Raceway Pulling Tension Calculator

by Gerald Newton
January 17, 2000

The Calculator uses Equations based on a study by the ICEA.

Observations:

The radius of bend does not effect the pulling tension.

The size of raceway does not effect the pulling tension or the sidewall pressure. This assumes that the raceway is not overfilled and is in compliance with the NEC.

The sidewall pressure is effected by the coefficient of friction and the radius of the bend. The larger the radius the less the sidewall pressure.

For long pulls with larger conductors sweep bends are usually necessary to lower the sidewall pressure to within allowable limits. For these types of pulls radii of standard benders cause the sidewall pressure to exceed the maximum in most cases.

The end that is the farthest away from the bends will have the least pulling tension.

Bends have a multiplying effect on the incoming tension to the bend.

Although there are no ICEA data for pushing in conductors at the feed end there is substantial evidence that this method has a substantial effect on decreasing the total pulling tension at the pull end.

Wire Tension Pull Calculator for Straight Pulls
(Read reference material below for explanations.)
by electrician.com

Select Material	Select Size	Coefficient of Friction
Weight Multiplier	Number of Conductors	Enter Length in Feet
Adder/Subtractor weight multiplier
Circular mil area	Total Weight of one foot of wire(s)	Maximum Pulling Tension in Pounds
Maximum Pulling Length in Feet		Pulling Tension in Lbs.
************** **************
Wire Tension Pull Calculator for Curved Duct Section Use values found above (Break down runs into feed straight section, bend, pull straight section. See Example below.)
Enter tension at feeding end straight section	Enter total angle of bend in degrees	Enter radius of bend in inches
Enter tension at pulling end straight section		Coefficient of Friction

Required Total Tension in Lbs.	Sidewall Pressure in Lbs.	Maximum allowed Sidewall Pressure in Lbs.

**Recommended Coefficients of Friction**
Pulling Straight Up	1.0
Pulling Straight Down	0.0001
Pulling at a 30 or 45 degree angle	0.7
Pulling Horizontal and Curvature Pulls	0.5
Pulling Horizontal with Lubricant	.2

**Recommended Adder/Subtractor**
**weight multiplier**
For larger wires add 1.09, the default. This approximately compensates for the weight of the insulation.
If weight of 1 ft of wire(s) or cable(s) is known use the multiplier that gives the nearest weight per foot for all the wires or cables the same as known value. The default weight with multiplier set to 1.00 is 0.321 Lbs per cubic inch of copper and 0.10 Lbs. per cubic inch of Aluminum. The cubic inch per foot calculation is found from the circular mil area for the selected size of conductor. The weight and not the circular mil area is used in subsequent calculations for Pulling Tension. For other weights that are lighter, for instance fiber optic cables, use a negative multiplier. The weight multiplier uses the size of conductors as a reference only. This way the calculator can be used for calculating Pulling Tension for communications and fiber optic cables. The Maximum Pulling Tension is calculated as 0.008 times the circular mil area for copper and 0.006 times the circular mil area for aluminum. The Maximum Pull Tension and Maximum Pulling Length are not adjustable and would not be correct for fiber optic cables, but the Pulling Tension based on weight and coefficient of friction would be correct, likewise for the curvature calculator.

Example 1

This example is taken directly from the Southwire Cable Catalog

to prove that the Calculator is accurate.

This example will be done first using the given radius of 120 inches
then attempted using a Greenlee 881 with a radius of 16 inches.
It will be found that the 16 inch radius causes too high a sidewall pressure and that a 36 or 48 inch inch factory sweep will satisfy the given conditions.

Part I
Using Given Conditions
Step 1
Set add multiplier to 1.40 to get 6.35 Lb/Ft for conductor weight
for 3 1/C 500 kcmil
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 0.5
Length = 220 feet
Calculated pull tension = 635 Lbs.
Step 2
Calculate pull tension straight section past first 45 degree bend
Coefficient of Friction = 0.5
Length = 70 feet
Calculated pull tension = 222 Lbs.
Step 3
Calculate pull tension at first 45
Coefficient of Friction = 0.5
Pull tension at feed straight section = 635 Lbs.
Angle of Bend = 45 degrees
Radius = 120 inches
Pull tension at pull end straight section = 222 Lbs
Total Calculated pull tension = 1162 Lbs.
Sidewall pressure is 139 Lb.
Maximum allowed sidewall presure is 3000 Lb.
Step 4
Calculate pull tension at straight section past first 90
Coefficient of Friction = 0.5
Length = 100 feet
Calculated Pull Tension = 317
Step 5
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 1162 Lbs
Angle = 90 degrees
Radius = 120 inches
Pull Tension at pull straight section = 317
Total Calculated Pull Tension = 2865 Lb.
Sidewall pressure is 255 Lb.
Maximum allowed sidewall presure is 3000 Lb.
The example shows 2863 Lb.
There is a .07 per cent error that is accountable to round off error.

Part II
The same problem as Example I except with a radius of 16 inches.

Step 1
Set add multiplier to 1.40 to get 6.35 Lb/Ft for conductor weight
for 3 1/C 500 kcmil
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 0.5
Length = 220 feet
Calculated pull tension = 635 Lbs.
Step 2
Calculate pull tension straight section past first 45 degree bend
Coefficient of Friction = 0.5
Length = 70 feet
Calculated pull tension = 222 Lbs.
Step 3
Calculate pull tension at first 45
Coefficient of Friction = 0.5
Pull tension at feed straight section = 635 Lbs.
Angle of Bend = 45 degrees
Radius = 16 inches
Pull tension at pull end straight section = 222 Lbs
Total Calculated pull tension = 1162 Lbs.
Sidewall pressure is 705 Lb.
Maximum sidewall pressure allowed is 300 x 1.333 = 400 Lb.
Try 36 inch radius factory sweeps and redo calculation.
Step 3 repeated with 36 inch radius
Calculate pull tension at first 45
Coefficient of Friction = 0.5
Pull tension at feed straight section = 635 Lbs.
Angle of Bend = 45 degrees
Radius = 36 inches
Pull tension at pull end straight section = 222 Lbs
Total Calculated pull tension = 1162 Lbs.
Sidewall pressure is 313 Lb.

Step 4
Calculate pull tension at straight section past first 90
Coefficient of Friction = 0.5
Length = 100 feet
Calculated Pull Tension = 317
Step 5
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 1162 Lbs
Angle = 90 degrees
Radius = 36 inches
Pull Tension at pull straight section = 317
Total Calculated Pull Tension = 2865 Lb..
Sidewall pressure is 849 Lb.
Maximum sidewall pressure allowed is 900 Lb.

Example 2

Find the best method to Pull the Conductors.

Figure Shows Vertical Plane

For a Floating Window with the Pull Calculator Click Here.
(can be readily applied to the examples as you move through them)

Method I
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 1.0
Length = 18 feet
Calculated pull tension = 83 Lbs.
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .5
Length = 20 feet
Calculated pull tension = 46 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 83 Lbs.
Angle of Bend = 90 degrees
Radius = 18 inches
Pull tension at pull end straight section = 46 Lbs
Total Calculated pull tension = 228 Lbs.
Step 4
Calculate pull tension at straight section past second 90
Coefficient of Friction = .0001
Length = 10 feet
Calculated Pull Tension = 0
Step 5
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 208 Lbs
Angle = 90 degrees
Radius = 18 inches
Pull Tension at pull straight section = 0
Total Calculated Pull Tension = 499 Lbs.

Step 6
Calculate last 10 feet of straight section to find contributing weight.
Coefficient of Friction = 1.0
Length = 10 feet
Calculated pull tension = 46 Lbs.
Total Tension Required after conductors arrive at pull end.
499 - 46 Lbs = 453 Lbs.
Pull tension would decrease from 499 to 453 Lbs after conductors passed second 90.
Method II
Use second person that pushes 50 Lbs at feed end
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 1.0
Length = 18 feet
Calculated pull tension = 83 Lbs.
With 50 Lb. push
Pull tension = 83 - 50 = 33 Lbs.
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .5
Length = 20 feet
Calculated pull tension = 46 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 33 Lbs.
Angle of Bend = 90 degrees
Radius = 18 inches
Pull tension at pull end straight section = 46 Lbs
Total Calculated pull tension = 118 Lbs.
Step 4
Calculate pull tension at straight section past second 90
Coefficient of Friction = .0001
Length = 10 feet
Calculated Pull Tension = 0
Step 5
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 118 Lbs
Angle = 90 degrees
Radius = 18 inches
Pull Tension at pull straight section = 0
Total Calculated Pull Tension = 258 Lbs.

Step 6
Calculate last 10 feet of straight section to find contributing weight.
Coefficient of Friction = 1.0
Length = 10 feet
Calculated pull tension = 46 Lbs.
Total Tension Required after conductors arrive at pull end.
258 - 46 Lbs = 212 Lbs.
Pull tension would decrease from 258 to 212 Lbs after conductors passed second 90.

Method III Reverse Pull and Feed Ends
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 1.0
Length = 10 feet
Calculated pull tension = 46 Lbs.
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .5
Length = 20 feet
Calculated pull tension = 46 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 46 Lbs.
Angle of Bend = 90 degrees
Radius = 18 inches
Pull tension at pull end straight section = 46 Lbs
Total Calculated pull tension = 147 Lbs.
Step 4
Calculate pull tension at straight section past second 90
Coefficient of Friction = .0001
Length = 18 feet
Calculated Pull Tension = 0
Step 5
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 147 Lbs
Angle = 90 degrees
Radius = 18 inches
Pull Tension at pull straight section = 0
Total Calculated Pull Tension = 322 Lbs.
Step 6
Calculate last 18 feet of straight section to find contributing weight.
Coefficient of Friction = 1.0
Length = 18 feet
Calculated pull tension = 83 Lbs.
Total Tension Required after conductors arrive at pull end.
322 - 83 Lbs = 239 Lbs.
Pull tension would decrease from 322 to 239 Lbs after conductors passed second 90.
Method IV Reverse Pull and Feed Ends
and use second person pushing 50 Lbs at feed end.
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = 1.0
Length = 10 feet
Calculated pull tension = 46 Lbs.
Pull tension = 46 - 50 = - 4 Lbs
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .5
Length = 20 feet
Calculated pull tension = 46 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = - 4 Lbs.
Angle of Bend = 90 degrees
Radius = 18 inches
Pull tension at pull end straight section = 46 Lbs
Total Calculated pull tension = 37 Lbs.
Step 4
Calculate pull tension at straight section past second 90
Coefficient of Friction = .0001
Length = 18 feet
Calculated Pull Tension = 0
Step 5
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 46 Lbs
Angle = 90 degrees
Radius = 18 inches
Pull Tension at pull straight section = 0
Total Calculated Pull Tension = 101 Lbs.
Step 6
Calculate last 18 feet of straight section to find contributing weight.
Coefficient of Friction = 1.0
Length = 18 feet
Calculated pull tension = 83 Lbs.
Total Tension Required after conductors arrive at pull end.
101 - 83 Lbs = 18 Lbs.
Pull tension would decrease from 101 to 18 Lbs after conductors passed second 90.
Summary:

Method Push at Feed
End in Lbs Pull Tension in Lbs.

I ( Fig 1) 0 499

II (Fig. 1 with 2 persons) 50 258

III (Reverse ends) 0 322

IV (Reverse ends with 2 persons) 50 101

Conclusion:
This problem demonstrates why "one push is worth four pulls."

Use Method IV if two people are available - Reverse Pull and Feed Ends in Figure 1 and use second person pushing at feed end.

Use Method III if two people are not available - Reverse Pull and Feed Ends in Figure 1.

Example 3

Radius of Bend = 16 inches for Greenlee 881 Bender

For a Floating Window with the Pull Calculator Click Here.
(can be readily applied to the examples as you move through them)

Method I
Pull from A to B
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = .0001
Length = 8 feet
Calculated pull tension = 0 Lbs.
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .2
Length = 80 feet
Calculated pull tension = 105 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 0 Lbs.
Angle of Bend = 90 degrees
Radius = 16 inches
Pull tension at pull end straight section = 105 Lbs
Total Calculated pull tension = 105 Lbs.
Step 4
Calculate pull tension at straight section past 60 degree kick
Coefficient of Friction = .2
Length = 6 feet
Calculated Pull Tension = 8
Step 5
Calculate pull tension at 60 degree kick
Coefficient of Friction = .5
Pull Tension at feed straight section = 105 Lbs
Angle = 60 degrees
Radius = 16 inches
Pull Tension at pull straight section = 8
Total Calculated Pull Tension = 185 Lbs.
Step 6
Calculate pull tension at straight past second 90
Coefficient of Friction = 1.0
Length = 6 feet
Calculated Pull Tension = 40
Step 7
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 185 Lbs
Angle = 90 degrees
Radius = 16 inches
Pull Tension at pull straight section = 40
Total Calculated Pull Tension = 445 Lbs.
Method II
Pull from A to B
Use Two persons pushing about 80 Lb. at A
This method was done by hand in Nome, Alaska in 1998 using three people,
at the FAA Station for D&N Electric out of Georgia.
Two persons pushed and one pulled with a rope. Gerald Newton was the puller.
The pull went smoothly until the last 90 that multiplied the tension from about 67 Lb. to 187 Lb. The last 90 was pulled using a unistrut lever bar on the rope. The 187 Lb. had to be pulled to get through the last 90 and it felt like 187 Lb. because it was just a little over what I can pull with the rope over my shoulders. This is the field scientific method!

Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = .0001
Length = 8 feet
Calculated pull tension = 0 Lbs.
Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .2
Length = 80 feet
Calculated pull tension = 105 Lbs.
With the 80 Lb push at A transferred around the 90
Pull tension = 105 - 80 = 35 Lb.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 0 Lbs.
Angle of Bend = 90 degrees
Radius = 16 inches
Pull tension at pull end straight section = 35 Lbs
Total Calculated pull tension = 35 Lbs.
Step 4
Calculate pull tension at straight section past 60 degree kick
Coefficient of Friction = .2
Length = 6 feet
Calculated Pull Tension = 8
Step 5
Calculate pull tension at 60 degree kick
Coefficient of Friction = .5
Pull Tension at feed straight section = 35 Lbs
Angle = 60 degrees
Radius = 16 inches
Pull Tension at pull straight section = 8
Total Calculated Pull Tension = 67 Lbs.
Step 6
Calculate pull tension at straight past second 90
Coefficient of Friction = 1.0
Length = 6 feet
Calculated Pull Tension = 40
Step 7
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 67 Lbs
Angle = 90 degrees
Radius = 16 inches
Pull Tension at pull straight section = 40
Total Calculated Pull Tension = 187 Lbs.

Method III
Pull from B to A
Step 1
Calculate pull tension at first straight section at Feed End.
Coefficient of Friction = .0001
Length = 6 feet
Calculated pull tension = 0 Lbs.

Step 2
Calculate pull tension straight section past first 90.
Coefficient of Friction = .2
Length = 6 feet
Calculated pull tension = 8 Lbs.
Step 3
Calculate pull tension at first 90
Coefficient of Friction = .5
Pull tension at feed straight section = 0 Lbs.
Angle of Bend = 90 degrees
Radius = 16 inches
Pull tension at pull end straight section = 8 Lbs
Total Calculated pull tension = 8 Lbs.
Step 4
Calculate pull tension at straight section past 60 degree kick
Coefficient of Friction = .2
Length = 80 feet
Calculated Pull Tension = 105
Step 5
Calculate pull tension at 60 degree kick
Coefficient of Friction = .5
Pull Tension at feed straight section = 8 Lbs
Angle = 60 degrees
Radius = 16 inches
Pull Tension at pull straight section = 105
Total Calculated Pull Tension = 119 Lbs.
Step 6
Calculate pull tension at straight past second 90
Coefficient of Friction = 1.0
Length = 8 feet
Calculated Pull Tension = 52
Step 7
Calculate pull tension at second 90
Coefficient of Friction = .5
Pull Tension at feed straight section = 119 Lbs
Angle = 90 degrees
Radius = 16 inches
Pull Tension at pull straight section = 52
Total Calculated Pull Tension = 313 Lbs.

For excellent References
try:
http://www.houwire.com/catalog/l-6.html
or
http://www.southwire.com/wc/catalog/sec61/61-03.pdf

Bending Radii and Pulling Tensions

Power Cables Without Metallic Shielding

The minimum bending radii for both single and multiple-conductor cable with or without lead sheath and without metallic shielding are as follows:

Minimum Bending Radius as a Multiple of Cable Diameter

Thickness of Conductor Insulation in Mils

Overall Diameter of Cable

Diameter in Inches

1,000 and Less

1,001 to 2,000

2,001 and Over

155 and less

170-310

325 and over

Power Cables With Metallic Shielding

For Tape Shielded Cables, the minimum bending radius for all cables with metallic shielding tapes is twelve times the overall diameter of the completed cable.
For Wire Shielded Cables, the minimum bending radius for all cables with wire shielding is eight times the overall diameter of the completed cable.

The following recommendations are based on a study sponsored by ICEA. These recommendations may be modified if experience and more exact information so indicate.

A. Maximum Pulling Tension On Cable

With pulling eye attached to copper conductors, the maximum pulling strain in pounds should not exceed 0.008 times cir-mil area.
With pulling attached to aluminum conductors, the maximum pulling strain in pounds should not exceed 0.006 times cir-mil area.

TM =0.008 x n x CM, for copper Done in Calculator

TM =0.006 x n x CM, for aluminum Done in Calculator

where

TM = max. tension, lb.

n = number of conductors

CM = cir-mil area of each conductor

With cable grip over lead sheath, the maximum pulling strain in pounds should not exceed 1500 lb./sq. inch of lead sheath cross-sectional area for commercial lead

TM=4712 x t x (D-t), where

t = sheath thickness, inches

D = overall diameter of cable, inches

With cable grip over non-loaded cable, the maximum pulling strain should not exceed 1000 lb. and may not exceed the maximum tension based on 0.008 or 0.006 x total conductor area.
Where more than three conductors are pulled together, reduce the pulling tension 20%. Done in Calculator

B. Maximum Permissible Pulling Length

LM = TM/(C x W) Done in Calculator

where
LM = pulling length, feet (straight section)
TM = maximum tension, lb.
W = weight of cable per foot, lb.
C = coefficient of friction (usually 0.5)

C. Pulling Tension Requirements in Ducts

For straight duct sections, the pulling tension in pounds equals the length of duct multiplied by the weight per foot of cable and the coefficient of friction (paragraph B, above).
For curved duct sections, the following formula applies:

Tt= T2 + T1 x e^fa Done in Calculator

where

T2 = tension for straight section at pulling end, lb.

T1 = tension for straight section at feeding end, lb.

Tt = total tension

a = angle of bend in radian (1 radian = 57.3 deg.)

f = coefficient of friction (usually 0.5)

e^fa = log10^-1 x (fa)/2.303

e^fa = The number whose logarithm to the base ten is fa/2.303

e = Naperian logarithm base (= 2.718)

The value of e^fa can be found using JavaScript:

Math.pow(value1, value2)

where value1 = 2.718 and value2= fa

The maximum pulling tension in pounds shall not exceed 300 times the radius of curvature of the duct expressed in feet.

D. Sidewall Pressure

Sidewall Pressure = T / R Done in Calculator
Where
T = Pulling Tension out of bend
R = Radius of bend in feet

E. Pulling Tensions Must Not Exceed The Smaller of These Values:

Allowable tensions on conductor.
Allowable tensions on pulling device.
Allowable sidewall pressure.

Pulling Eye: T (Cu) = Number conductors x circular mills x .008

Basket-Grip: T = 1000 lbs. per grip

Sidewall Pressure: P = 300 pounds x radius of curve in feet.

Center Radius for Greenlee Benders
Bender	1/2"	3/4"	1"	1-1/4"	1-1/2"	2"
Site-Rite Hand Bender	4-3/16"	5-1/8"	6-1/2"	11"
Site-Rite II Hand Bender	4-3/16"	5-1/8"	6-1/2"	9-5/8"
555 EMT	4-1/4"	5-3/8"	6-3/4"	8-3/4"	8-9/32"	9-3/16"
555 IMC	4-3/8"	4-1/2"	5-3/4"	7-1/4"	8-1/4"	9-1/2"
555 Rigid	4-3/8"	4-1/2"	5-3/4"	7-1/4"	8-9/32"	9-3/16"
854 / 855 EMT	4-5/16"	5-1/2"	7"	8-13/16"	8-3/8"	9-1/4"
854 / 855 IMC/Rigid	4-1/4"	5-7/16"	6-15/16"	8-3/4"	8-1/4"	9"
880	4"	4-1/2"	5-3/4"	7-1/4"	8-1/4"	9-1/2"
882 EMT	--	--	--	7-7/32"	8-1/16"	9-5/16"
882 IMC / Rigid	--	--	--	7-1/4"	8-1/4"	8-7/8"
1800 / 1801 Rigid & IMC	2-5/8"	4-5/8"	5-7/8"	8-1/16"	9-11/16"

Bender	1-1/4"	1-1/2"	2"	2-1/2"	3"	3-1/2"	4"	5"
777	7-1/4"	8-1/4"	9-1/2"	11-7/16"	13-3/4"	16"	18-1/4"
881				13-1/2"	16"	18-5/8"	20-7/8"
884 / 885	7-1/4"	8-1/4"	9-1/2"	12-1/2"	15"	17-1/2"	20"	25"

Decimal Equivalents
1/16	.0625
1/8	.125
3/16	.187
1/4	.250
5/16	.312
3/8	.375
7/16	.437
1/2	.500
9/16	.562
5/8	.625

Method	Push at Feed End in Lbs	Pull Tension in Lbs.
I ( Fig 1)	0	499
II (Fig. 1 with 2 persons)	50	258
III (Reverse ends)	0	322
IV (Reverse ends with 2 persons)	50	101