2000 amp service

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don_resqcapt19

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Location
Illinois
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retired electrician
Well we disagree with your statement heres why first ive been in the electrical trade for over 35 years and in the field working as a electrician same company for 26 years my crew only does power distribution work.
We install all underground work and we pull all the feeders on every job if you pull wire in a 4 inch conduit the pulling force is less then in a 3 1/2 inch conduit .
I dont need a formula to tell me this i know .
I have been in the trade for the same time and have made many large pulls and I see little difference between the pulling force for a code minimum conduit and an oversized conduit.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well so what were saying is that the same wire size in a raceway same length same offsets or bends and the pulling force calculated by a formula is correct that there is no difference in pulling force ?

And this is always the case meaning 90 degree elbows are standard sized not sweeps or long radi types the formula is still correct for pulling force ?

Pulls of what size conductors or cables did you pull ? We just dont see how a formula can calculate this to be the same force do you have a formula that i can see because ive never seen this .

maybe we could use this at work this week were pulling 4 x 750 mcm copper in 4 inch conduit 400 feet thur a pull box its a straight run 2x90s sweeps rigid conduit and there is 55 runs 11 per transformer . We would like to see what the formula would be for these and will test it out . Now if they were in 6 inch conduit it would not make any difference in the force correct ? Because we have one run of 11 which has larger conduits installed for future runs and we will be pulling this week it would be nice to test your theory out ?


Take care please send me that formula
 

iwire

Moderator
Staff member
Location
Massachusetts
Take care please send me that formula

Observations:

  • The radius of bend does not effect the pulling tension.
  • The size of raceway does not effect the pulling tension or the sidewall pressure. This assumes that the raceway is not overfilled and is in compliance with the NEC.
  • The sidewall pressure is effected by the coefficient of friction and the radius of the bend. The larger the radius the less the sidewall pressure.
  • For long pulls with larger conductors sweep bends are usually necessary to lower the sidewall pressure to within allowable limits. For these types of pulls radii of standard benders cause the sidewall pressure to exceed the maximum in most cases.
  • The end that is the farthest away from the bends will have the least pulling tension.
  • Bends have a multiplying effect on the incoming tension to the bend.
  • Although there are no ICEA data for pushing in conductors at the feed end there is substantial evidence that this method has a substantial effect on decreasing the total pulling tension at the pull end.

Raceway Pulling Tension Calculator

Simple Calculations for Pulling Cable from EC&M
 

iwire

Moderator
Staff member
Location
Massachusetts
Ohm, I don't have 35 years in but I have also pulled some big copper.

Here is a job where I reduced the 4" EMT on the prints down to 3" EMT to make it easier to fit the rack of 5 EMTs into the existing crowded suspended ceiling.

The EE asked for calculations showing that the 3" would be OK. I used the info from the links I posted above to do that.

It was four 500 kcmil XHHW copper and EGC in 3" EMT. The guys pulling it said it went in fine.

000_0878.jpg




000_0879.jpg
 
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don_resqcapt19

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Location
Illinois
Occupation
retired electrician
Well so what were saying is that the same wire size in a raceway same length same offsets or bends and the pulling force calculated by a formula is correct that there is no difference in pulling force ?
I didn't say there was no difference, I said there is very little difference.

And this is always the case meaning 90 degree elbows are standard sized not sweeps or long radi types the formula is still correct for pulling force ?
The radius of the bend also has little effect on the pulling force, however it has a huge effect on the sidewall pressure that can damage the conductor insulation. In most pulls the limiting factor is the sidewall pressure and not the actual pulling tension.

maybe we could use this at work this week were pulling 4 x 750 mcm copper in 4 inch conduit 400 feet thur a pull box its a straight run 2x90s sweeps rigid conduit and there is 55 runs 11 per transformer . We would like to see what the formula would be for these and will test it out . Now if they were in 6 inch conduit it would not make any difference in the force correct ? Because we have one run of 11 which has larger conduits installed for future runs and we will be pulling this week it would be nice to test your theory out ?
You would have to run the pulling calcs and compare them to the actual measured pulling force.

Take care please send me that formula
Bob has provided links.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
As an engineer, I assume that if I keep the conduits to the NEC minimum size, that the wires can be installed with undue trouble. However, as the contractor and bidder, I think you are free to upsize the conduits however you see fit if you think it will save enough labor to make a difference.

I like to give the contractors some freedom to do the most efficient installation possible. Contractor A may install it as we show it, Contractor B may upsize the conduit a notch, and Bob likes to downsize the conduits.
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
EEs like to cover their rear and I don't blame them a bit, it is really what they are paid for but at the same time I have seen a lot of what looks like waste to me. :smile:

I couldn't agree more about 200% neutrals being largely hype. I might upsize a neutral for a branch circuit, or even a panelboard, but upsizing the neutral on a service is just plain crazy. The NEC load calculations are probably twice what the peak load will be anyway. Combine that along with all the HVAC equipment that doesn't even use the neutral, and there isn't any sense in upsizing a service neutral.

But I have to add, its not just the engineers that have bought into this. Many electricians embrace larger neutrals just as much as the engineers do.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well here is a few pipes we ran up into a control room tower at a plant lets calculate these !
Just joken, but yes we see your point but never have we used a formula we just pull we use a tension meter if needed and use the greenlee pound gauge if needed and lots of soap and many years of pulling .
I will read more on these calculations its interesting to me to still learn what others do dont get me wrong i still learn everyday new tricks http://i611.photobucket.com/albums/tt195/stringking/pipes001.jpg . guess you can tell by the picture it is not a digital its pretty old . Take care best to yas
 

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
ohm,
If you don't do pulling calcs, how do you know that you are not exceeding the maximum permitted sidewall pressure?
 

ohmhead

Senior Member
Location
ORLANDO FLA
ohm,
If you don't do pulling calcs, how do you know that you are not exceeding the maximum permitted sidewall pressure?

Well lets look at this from a non formula or non calculated or any probability in mathematics when we didnt have computers or the NEC was only a thin book and there was no electricians schools like we have today or a forum to talk with other electricians all over the USA . We just pulled the wire !!
 
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