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Question Horizontal Angle segment ductbank "Pulling Cable" Module Etap Software
- Thread starter intelsath
- Start date
Palletjack
Electrical
Question to think about.
This program says “This is the turning or bending angle of the conduit at each bend in degrees”
How many 95 degree conduit bends have you worked with?
Manufacturers don’t make 95 degree conduit bends.
At least none I have ever worked with.
This program says “This is the turning or bending angle of the conduit at each bend in degrees”
How many 95 degree conduit bends have you worked with?
Manufacturers don’t make 95 degree conduit bends.
At least none I have ever worked with.
I'm not familiar with the ETAP module for this, but this calculation is not terribly complicated. We used to use Pull-planner marketed by Polywater and found it worked quite well. Before that, we used an Excel spreadsheet. Don't forget to calculate in both directions!
Cheers,
Dave
Cheers,
Dave
- Thread starter
- #4
davidbeach
Electrical
As I said elsewhere, a freely turning sheave, properly aligned, should be able to be ignored. It's certainly very, very, different than a similar pull against the unmoving sidewall of an elbow.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
I’ll see your silver lining and raise you two black clouds. - Protection Operations
- Thread starter
- #6
- Moderator
- #7
When a cable is pulled around a 90 degree bend there are three drags to be considered:
The friction of the cable against the side of the bend.
The force to bend the radius in the cable as it starts into the bend.
The force to straighten the cable as it leaves the bend.
Pulling around a sheave is different.
If the sheave is rigged properly it is free to swing in the plane of the bend.
As the cable starts to move, it does not bend freely around the sheave.
You have three vectors;
The cable coming in,
The cable leaving,
The single cable, chain or strap restraining the sheave.
As the cable starts to move, the incoming vector extends, the outgoing vector shortens and the vector restraining the sheave pivots.
The farther the sheave is displaced, the greater the force trying to bend the cable around the sheave.
The pulling force increases as this is happening.
When the forces pass equilibrium, the sheave starts to roll along the cable quite quickly so as to reduce the displacement force.
With a large radius sheave the sheave may roll back along the cable as much as two or three feet.
Then the sheave starts to move with the cable again and the cycle repeats.
The advantage is that when there is more than one sheave on a long pull, they cycle in random and the pulling force is reduced.
I have seen long pulls with multiple 90 degree sheaves with great care taken to fasten each sheave rigidly in place.
They were actually pulling the end off of the cable.
I was not in a position to intervene.
Eventually they positioned 30 or 40 electricians along the pull and pulled the cable in manually, in sections.
I am sure that with properly mounted sheaves the pull could have been completed faster with a much smaller crew.
Yes I have seen large cable pulled successfully and have participated in the setup for some of them.
Bill
--------------------
"Why not the best?"
Jimmy Carter
The friction of the cable against the side of the bend.
The force to bend the radius in the cable as it starts into the bend.
The force to straighten the cable as it leaves the bend.
Pulling around a sheave is different.
If the sheave is rigged properly it is free to swing in the plane of the bend.
As the cable starts to move, it does not bend freely around the sheave.
You have three vectors;
The cable coming in,
The cable leaving,
The single cable, chain or strap restraining the sheave.
As the cable starts to move, the incoming vector extends, the outgoing vector shortens and the vector restraining the sheave pivots.
The farther the sheave is displaced, the greater the force trying to bend the cable around the sheave.
The pulling force increases as this is happening.
When the forces pass equilibrium, the sheave starts to roll along the cable quite quickly so as to reduce the displacement force.
With a large radius sheave the sheave may roll back along the cable as much as two or three feet.
Then the sheave starts to move with the cable again and the cycle repeats.
The advantage is that when there is more than one sheave on a long pull, they cycle in random and the pulling force is reduced.
I have seen long pulls with multiple 90 degree sheaves with great care taken to fasten each sheave rigidly in place.
They were actually pulling the end off of the cable.
I was not in a position to intervene.
Eventually they positioned 30 or 40 electricians along the pull and pulled the cable in manually, in sections.
I am sure that with properly mounted sheaves the pull could have been completed faster with a much smaller crew.
Yes I have seen large cable pulled successfully and have participated in the setup for some of them.
Bill
--------------------
"Why not the best?"
Jimmy Carter
Palletjack
Electrical
I’m in agreement with waross and davidbeach on this one. Your making this harder than it really is...
Don’t forget three things:
maximum sidewall pressure; minimum bending radii and maximum pulling tensions.
Most people when ordering or installing sheaves tend to forget the second one.
Also if there is someone feeding or pushing the wire at the reel make sure the reel tension number is 0 or negative.
Don’t forget three things:
maximum sidewall pressure; minimum bending radii and maximum pulling tensions.
Most people when ordering or installing sheaves tend to forget the second one.
Also if there is someone feeding or pushing the wire at the reel make sure the reel tension number is 0 or negative.
davidbeach
Electrical
“Reel tension is 0 or negative...” Except when you’re making a long downhill pull with lots of lube. 
Designed a job once that basically couldn’t be pulled uphill, but also couldn’t be safely pulled downhill without reel brakes.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
Designed a job once that basically couldn’t be pulled uphill, but also couldn’t be safely pulled downhill without reel brakes.
I’ll see your silver lining and raise you two black clouds. - Protection Operations
For Pull-Planner, check I think it used to be free, IIRC, but not sure about now.
- Moderator
- #11
We pulled some 3600MCM single conductor lead sheathed cable into ducts one time.
Yes, 3.6 million circular mills. I still have a 4 inch long souvenir of the cable hidden away somewhere.
We had a small forklift truck pushing the cable into the duct.
The duct entry was more or less horizontal and low.
We had a very close call.
The tugger exploded.
The drive chain broke and the rope tension caused a back spin. The chain doubled up and smashed the aluminum alloy chain guard.
We were working in a hot underground substation.
There was pieces of aluminum and broken chain flying past hot 13 kV bus bars.
Fortunately nothing lit up.
Bill
--------------------
"Why not the best?"
Jimmy Carter
Yes, 3.6 million circular mills. I still have a 4 inch long souvenir of the cable hidden away somewhere.
We had a small forklift truck pushing the cable into the duct.
The duct entry was more or less horizontal and low.
We had a very close call.
The tugger exploded.
The drive chain broke and the rope tension caused a back spin. The chain doubled up and smashed the aluminum alloy chain guard.
We were working in a hot underground substation.
There was pieces of aluminum and broken chain flying past hot 13 kV bus bars.
Fortunately nothing lit up.
Bill
--------------------
"Why not the best?"
Jimmy Carter
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