Pulling cable through underground ductwork.

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Discussion Overview

The discussion revolves around the challenges and considerations involved in pulling heavy-duty underground cables through ductwork, focusing on the effects of pulling speed and techniques. Participants explore the physical factors influencing cable pulling, including momentum, friction, and methods of cable management.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • The original poster (OP) questions the physical factors at play when pulling cable at different speeds and the implications of starting from a dead stop.
  • Some participants suggest that sideways momentum is significant and recommend pulling at a speed below the S-wave sound velocity in the cable to avoid dynamic issues.
  • Concerns are raised about static versus sliding friction, noting that stopping the pull increases the challenge due to static friction being greater.
  • Questions are posed about the methods used for pulling, such as whether the cable is pulled directly from a spool or laid out to avoid complications.
  • There is a mention of using lubricants, like soapy water, to facilitate the pulling process.
  • One participant inquires if using a rope with a diameter slightly greater than the cable improves success in pulling.

Areas of Agreement / Disagreement

Participants express differing views on the implications of pulling speed and techniques, with no consensus reached on the best practices or the physical factors involved. The discussion remains unresolved due to the complexity of the topic and the potential safety concerns raised.

Contextual Notes

The discussion is limited by the lack of detailed analysis from basic principles, and there are unresolved concerns regarding safety and liability in discussing the practical aspects of cable pulling.

Fatboyx
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TL;DR
Pulling cable through underground ductwork
Hello all,

I am an Engineering dropout turned Cable Splicer. In my job we do a lot of Heavy Duty underground cable pulling. Usually plastic jacketed cable through some type of ductwork (typically plastic as well). We use a winch truck and a heavy rope to pull this cable through the ducts, typically not more than 500 feet.

As of late our Foremans insistence on pulling the cable at a considerate speed has resulted in some botched jobs and what I consider to be an increased hazard. He claims that slowing down or stopping should only occur in an absolute emergency and likes to reference starting from a deadstop is like trying to start a train.

My question for you all:
- What would be the physical factors at play here?
- How substantial of a difference is it? pulling fast, slow, or from a dead stop.
- General conclusions and opinions?

I'm thinking momentum seems to be fairly negligible comparing a fast vs slow pull. Obviously coefficient of friction and how much cable is already in the ducts would be a factor as well.

Thanks for your help
-Chris
 
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Welcome to PF.

Fatboyx said:
I'm thinking momentum seems to be fairly negligible comparing a fast vs slow pull.
Sideways momentum will be important.

If you can pull slow and steady, you will avoid complex dynamic behaviour of the cable as it enters the duct. Pull at well below the S-wave sound velocity in the cable.

Do you pull directly from a spool, or do you lay out the cable, so it can enter without un-spooling, or suffer a major change of direction?

Once you stop, you will be faced with the static friction coefficient. That will be worse than the sliding friction coefficient.

Do you use lubricant? Soapy water?

Do you have greater success by pulling with a rope having a diameter slightly greater than the cable?
 
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Thread closed temporarily for Moderation...
 
After a Mentor discussion, the thread will remain closed. @Fatboyx -- We cannot allow discussion of dangerous activities at PF. Here is some of the Mentor discussion about this thread start of yours:

This problem is not easily analyzed from basic principles, and we cannot comment because of liability.

Point out that experience (the "botched jobs") is pretty much is conclusive.

The OP should be very careful about challenging the boss...

Thread will remain closed.
 
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