Pulling Calculations

[Ansel]

I have never used pulling calculations for communications cable. I have to calculate the maximum pulling tension for 24 Cat5e cables in 2" conduit. The cable size in diameter 0.24" overall with jacket. The conduit fill ends up being 37.5%. Each cable has 8 24AWG conductor. When I calculated the maximum pulling tension with 80% use, I calculated it to be 496.43 lb/force. I have read from the manufacturer that it should not exceed 25lb/force. I used two of the online pulling calculators and saw that it exceeded the 25lb/force. Am I doing this completely wrong?

 

[LarryFine]

Don't know, unless that's a per-wire number. 25 x 24 = 600.

 

[retirede]

Don't know, unless that's a per-wire number. 25 x 24 = 600.

I think that’s right, but don’t know how to ensure the force is distributed equally per cable.

 

[gadfly56]

I think that’s right, but don’t know how to ensure the force is distributed equally per cable.

That's a good question. It stands to reason that only the cables on the outside of the bundle are seeing any friction force, those on the interior are just along for the ride.

 

[topgone]

That's a good question. It stands to reason that only the cables on the outside of the bundle are seeing any friction force, those on the interior are just along for the ride.

Instead of going thru the hassle of calculating, why doesn't the OP use a cable pulling grip/basket? Doesn't cost much and ease in cable pulling is achieved. It ensures you don't damage cables due to excessive forces. No need to calculate, just make sure the number of cables pulled are within the charts.

 

[retirede]

Instead of going thru the hassle of calculating, why doesn't the OP use a cable pulling grip/basket? Doesn't cost much and ease in cable pulling is achieved. It ensures you don't damage cables due to excessive forces. No need to calculate, just make sure the number of cables pulled are within the charts.
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The way I read his OP, he is required to do a calculation, maybe the customer has an engineer requiring it???

 

[Ansel]

Client is requiring us to give calculations.

 

[kingpb]

Instead of going thru the hassle of calculating, why doesn't the OP use a cable pulling grip/basket? Doesn't cost much and ease in cable pulling is achieved. It ensures you don't damage cables due to excessive forces. No need to calculate, just make sure the number of cables pulled are within the charts.
View attachment 21840

I don't follow on how you can use a basket grip and not damage cable by to much tension or s sidewall pressure? Using a grip doesn't change cable weight, bends, or coefficient of friction.

 

[Ansel]

I have read that in many articles that there are confusion in the number for pulling tension when it is in a bundle. Some say it is 25lbf no matter how many cables are bundles. Some say that 25lbf is multiplied by the number of cables. I am not sure what to use.

 

[kingpb]

The formula for a single cable is;

T_c = S * A (lbs) and T_c = T_cable

where:
T_c - tension on each conductor in lbs
S - allowable stress in lbs/cmil
A - area of each conductor in cmil

Multiple conductors (two or three) in parallel or multiplexed and multiple conductor cables;

T_cable = N*T_c

Where N - No. of cables/conductors

More than 3;

T_cable = (0.8) *N*T_c

So, you can see that for more than 3 you apply the 0.8 factor. Thus in your case the T_cable = 0.8 * 24 x 25 (lbs) = 480 (lbs)

And therefore the tension in your 2" conduit route cannot exceed 480 lbs.