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• DATE:
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April 13, 2016

NWPPA E&O Conference Spokane, WA

Underground Cable Pulling Calculations

Joseph W McAuliffe PE Senior Product Engineer

Cable Pulling Calculations

• Information needed
• Calculation High Points
• Impact of Design Decisions
• Cable Handling
• Duct Systems Impact on Cable Pulling
• Field set up and Pulling Procedures
• After the Pull

Cable Pulling Calculations

• Information Needed
• Conduit Type and Size
• Cable Type
• Cable Weight and Dimensions
• Type of Jacket
• Number of Bends
• Location in the Pull
• Radius of each Bend
• Any Elevation Changes

Cable Pulling Calculations

• What will impact ultimate pulling tension
• Coefficient of Friction
• Pulling Lube
• Amount (or lack of Use)
• Back Tension
• Placement of bends
• Duct installation itself

Cable Pulling Calculations

• Factors that need to be checked
• Jamming
• Cable clearance
• Minimum Bending Radius
• Side Wall Bearing Pressure
• Weight (Weight Correction Factor)
• Pulling Tension

Cable Pulling Calculations

• Jamming
• J= D/d
• J Jam Ratio
• D = Inside diameter of Duct
• d = Cable diameter

Jamming can occur when ratio between 2.8 and 3.0

Cable Pulling Calculations

• Cable Clearance
• Single Conductor
• C = D – d’
• 3 Conductor (Based on Triangular Configuration)
• d’ = 1.05d

Cable Pulling Calculations

• Bending Radius
• Depends on cable construction
• Non-shielded depends on insulation thickness
• For shielded cables depends on type of shield
• Values stated are for permanent training.
• Effects side wall bearing pressure
• Recommend 20X OD for conduit bends

Cable Pulling Calculations

• Cable Weight (Weight Correction Factor)
• Single conductor
• Three Conductor
• Cradled
• Triangular
• Can be determined from Jam Ratio

Cable Pulling Calculations pulled around a conduit bend

• Sidewall Bearing Pressure
• Radial force that is exerted on a cable being

1 Single Cable: SP = T/ R 3 Single Cables (cradled) SP = (3w – 2) (T / 3R) 3 Single Cables (triangular) SP = w (T / 2R)

T = Tension coming out of the bend, Tout (lbs) R = Bend Radius (ft) w = Weight Correction Factor

Cable Pulling Calculations

• Allowable Pulling Tension
• Conductor Type (CU or AA)
• Conductor Size
• Pulling attachment
• Pulling Eyes
• Basket Grip

Cable Pulling Calculations

• 3 Conductor Pull
• Only figure stress from 2 conductors
• With Pulling Eye
• Basket Grips
• 1000# (or conductor tension limit if lower)

Cable Pulling Calculations

• Actual calculations
• All results are cumulative
• Start with the back tension on the reel
• Elevation angles are degrees
• Bend sections are radians
• Side wall bearing pressure is often the limit
• Always calculate from both ends

• Would it be easier to pull cable from A to B or

B to A?

A B 300 30 20 20 50

Courtesy American Polywater

Cable Pulling Calculations

URD Cable Pulling

• Cables supplied to utilities are the best that they

have ever been

• Proper handling, Installation, termination,

protection and operation are all critical to long term reliability

• Field personnel can greatly impact the

reliability of the system

• Cable handling
• What’s wrong with these pictures?

URD Cable Pulling

• Proper Reel handling is important

URD Cable Pulling

• Proper Reel Handling

URD Cable Pulling

Do This Not This

• Duct Installation
• Understand the layout
• Old System
• Occupied before?
• What was cable removal like?

URD Cable Pulling

• Empty before?
• Is the Duct Clear?
• Is the Duct intact?
• Do you know the Layout?

• Duct Installation
• Understand the Layout
• They all look the same

when they are buried

URD Cable Pulling

• Duct Preparation
• Ensure the duct is clean
• Run a brush through the entire length
• Removes dirt and clutter
• Clean ducts allow for easier pulls

URD Cable Pulling

• Duct Preparation:
• Run a mandrel through the duct to know the condition
• This will help remove obstructions
• Ensure that the duct is round
• Whether New or Old

URD Cable Pulling

• Field Setup
• Know what to expect
• Have pulling calculations been run?
• Where are the bends?
• Can make a big difference in the pull
• As far as practical bends should be at the

beginning of the pull

• Down hill is better that up hill

URD Cable Pulling

• Field Setup
• Reels should be positioned for correct pay off
• Cable should be bent in one direction only
• Do not “S” the cable into the duct

URD Cable Pulling

URD Cable Pulling

Field Set up

This

• Field Set up

Not This

URD Cable Pulling

• Field Set up
• Sheaves
• Use of sheaves should be limited to

guiding cables

• Minimum bending radius must be

maintained

URD Cable Pulling

URD Cable Pulling

• Field Set up
• Always have end caps on cable ends
• During installation and before termination

URD Cable Pulling

• Installation
• Pulling cables
• Do not exceed maximum allowable pulling tension
• Do not exceed maximum SWBP
• Use proper amount of Pulling Lube
• Pull with a capstan whenever possible
• Max pulling speed should be 40 ft/min
• Do not stop a pull unless absolutely necessary
• Make sure cable ends are sealed when cut
• Sacrifice the first 10ft of cable when pull complete

URD Cable Pulling

• Installation
• Racking in Manholes
• Do not over bend the cables
• Support the cables as they follow the walls
• Ensure cables are tied down
• Must be able to move

URD Cable Pulling

• Installation
• Racking in enclosures
• Make sure there is enough slack for
• peration and possible repair

URD Cable Pulling

• Installation
• Termination
• Splices, elbows or terminations
• Use proper tools
• Follow directions
• Do not over stress

URD Cable Pulling

• QUESTIONS?