February 11, 2016
Work Smarter, Not Harder

Posted by: Lee Bedingfield

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Sometimes we all need a little “grandpa wisdom” so here’s a little tidbit that may help you out.  When visiting a MaxCell® installation, if you find yourself in the position of being a project manager, here's some advice you will appreciate.  If the situation warrants, the direction you pull can make things easier especially if you have 90o or 450 degree sweeps in your application which is often the case.  Let’s look at a straight pull and the equation for tension.  If I’m pulling in a straight line then the equation is as follows:

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From the above, incoming tension Tin remains unchanged by pulling direction.  The final tension Tout is a result of pull length multiplied by cable weight and COF.  Thus for a horizontal and flat duct run either direction doesn’t affect pulling tension.  If we introduce bends then everything changes including the equation because you have to factor in the bend as an additional variable.

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From the above equation we see that bends multiply the incoming tension.  So if there is a long pull before the bend that tension will be multiplied.  Therefore, the shorter the distance to the bend, the less the bend can add to the final tension so you need to set up the reel at B and pull to A.

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In summary, we don’t always have control over which way the cable is installed.  Sometimes the traffic and landscape dictates where the installer sets up the cable reel but if there is an option always set up the reel closest to the bend in the run.

 

*MaxCell® is a registered trademark of TVC Communications, a division of WESCO Distribution, Inc.


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