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Wire and Cable Pulling Tensions

Cable damaged during installation can cause service failures. Calculations should be made to indicate whether the pull looks easy or impossible. When a marginal situation is encountered, the entire pull should be reviewed. A final decision should be made based on factors known to the end user and installer. Pulling tensions may be evaluated by determining the maximum tension based on the pulling device used, and the maximum tension that can be applied to the conductors. The lesser of these two values is the maximum allowable tension. After calculating the pulling tensions, sidewall pressures may be calculated.

Do not exceed the allowable tension stated by the manufacturer of the pulling device or 10,000 pounds, whichever is less. Do not use metallic shielding wires, tapes or braids, or armor not designed for the purpose, in pulling tension calculations.

FORMULAS

SINGLE CONDUCTOR:
T = S * A (pounds)

Where:
T = conductor tension, lbs
S = conductor stress, lbs/cmil (Table 1)
A = conductor area, cmil (Table 2)

MULTIPLE CONDUCTORS:

T = N * S * A (pounds) for 3 or less conductors
T = (0.8) * N * S * A (pounds) for more than 3 conductors

Where:
N = number of conductors

NOTE: Pulling different conductor sizes at the same time is not recommended if the conductor size or other cable characteristics are significantly different. If different size conductors must be pulled, it must be done with care.

 

TABLE 1
MAXIMUM ALLOWABLE CONDUCTOR STRESS

 Cable Type

 Material

 Temper

 lbs/cmil

 All

 Copper

 Soft

 0.008

 Power

 Aluminum

 Hard

 0.008

 Power

 Aluminum

 3/4 Hard

 0.006

 Power

 Aluminum

 AA-8000

 0.006

 URD

 Aluminum

 1/2 Hard

 0.003

 Solid

 Aluminum

 Soft

 0.002

Note: 3/4 hard aluminum is allowed for power cable. The 1990 NEC defines use of AA-8000 for solid (8, 10 & 12 AWG) and stranded (8 AWG through 1000 kcmil) conductors.

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TABLE 2
CONVERSION FROM AWG to CMIL
(Solid and concentric stranded Aluminum and Copper conductors)

AWG

cmil

12

6,530

10

 10,380

 8

 16,510

 6

 26,240

 4

 41,740

 3

 52,620

 2

 66,360

 1

 83,690

 1/0

 105,600

 2/0

 133,100

 3/0

 167,800

 4/0

 211,600

kcmil

cmil

 250

 250,000 

 300

300,000

 350

350,000 

 400

400,000

 500

 500,000

 600

 600,000

 750

750,000

 800

 800,000

 1000

 1,000,000