# Calculate sag and maximum span



## garfield (Jul 30, 2009)

I'm quoting a job with 4 poles about 125 feet apart. How do I calculate the sag between the poles and how hard the wire will pull on the poles. As I read the code it appears I need to maintain an 18 foot height at the low point. I am planning on running #6 triplex. A large building is the starting point and I assume I need one guy wire at the corner of the "L" Basically this is an attempt to save money over boring or sawing parking lot.


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## garfield (Jul 30, 2009)

I was planning on square steel poles with 5 foot deep 24 inch diameter bases 30 feet tall.


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## drsparky (Nov 13, 2008)

Sorry, can't help you, I don't have a clue on this subject.


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## garfield (Jul 30, 2009)

The black sharpie line is the proposed install.


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## BBQ (Nov 16, 2010)

See if your library has the Lineman and Cableman's Handbook 

or buy it ..

http://www.amazon.com/Lineman-Cablemans-Handbook-Linemans/dp/0071467890


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## s.kelly (Mar 20, 2009)

Did you do a search on this? I remember something MD posted a while back that talked about this type of thing some. Mentioned a sagometer? I think. Never done this so I found it interesting. Not sure if the thread has what you need or not.


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## sparky970 (Mar 19, 2008)

garfield said:


> I'm quoting a job with 4 poles about 125 feet apart. How do I calculate the sag between the poles and how hard the wire will pull on the poles. As I read the code it appears I need to maintain an 18 foot height at the low point. I am planning on running #6 triplex. A large building is the starting point and I assume I need one guy wire at the corner of the "L" Basically this is an attempt to save money over boring or sawing parking lot.


I am bidding similar job using 45' wood poles and probably 250kcmil aluminum triplex. About 750' total.


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## Dennis Alwon (May 9, 2009)

If you know the local poco engineer I am sure they will be happy to help with figuring that.


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## Cletis (Aug 20, 2010)

*Line Sag*

Conductor Length
Application of calculus to the catenary equation allows the calculation of the conductor length,L(x) ,measured along the conductor from the low point of the catenary in either direction.The resulting equation becomes:

The formula for catenery is y = Cosh (H.x/c) and for Hyperbola is x^2/a^2 - y^2/b^2 = 1.

or 

Level span sag can be calculated by the approximate parabola method:

S = WcL^2 / 8Th

Where: S = Sag @ center of span in meters or feet; Wc = Weight of the conductor in kilograms per meter or pounds per foot; L = Span length in meters or feet and Th = Horizontal tension in Newtons or pounds. Obviously, the units chosen must be consistent.


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## Cletis (Aug 20, 2010)

*Cheat*

Or, if your lazy like me just use this one

http://www.spaceagecontrol.com/calccabl.htm


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## sparky970 (Mar 19, 2008)

s.kelly said:


> Did you do a search on this? I remember something MD posted a while back that talked about this type of thing some. Mentioned a sagometer? I think. Never done this so I found it interesting. Not sure if the thread has what you need or not.



http://www.electriciantalk.com/f7/sagging-conductors-stopwatch-155/


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## garfield (Jul 30, 2009)

Cletis these calculations are not in my current skill set.


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## Big John (May 23, 2010)

garfield said:


> Cletis these calculations are not in my current skill set.


 Don't worry, they're not in his skillset, either. :whistling2:

-John


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## sparky970 (Mar 19, 2008)

It'll take me a minute, I'm on my phone

www.csu.org/../appendix_c.pdf


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## bobelectric (Feb 24, 2007)

sparky970 said:


> I am bidding similar job using 45' wood poles and probably 250kcmil aluminum triplex. About 750' total.


You might do better using an xfmr.


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## sparky970 (Mar 19, 2008)

bobelectric said:


> You might do better using an xfmr.


It's feeding a 480v distribution panel, xfmr, and 120/208 panel.


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## garfield (Jul 30, 2009)

On mine I thought about boosting to 277 so I could use #8 duplex


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## SparkyinMontan (Sep 16, 2011)

Since there is an existing parking lot, I would bore it, personally. Don't like running such things overhead like that.

Aaron


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## sarness (Sep 14, 2010)

Don't forget about how much the poles are going to bend, especially that corner pole.


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## CDN EC (Jul 31, 2011)

Big John said:


> Don't worry, they're not in his skillset, either. :whistling2:
> 
> -John


:laughing: Oh man, this place is getting funnier by the day :laughing:


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## den (Mar 28, 2009)

we would go for min 100'-130' on # 6 before we would think about guying it. You can pull this up easy with one guy on a handline. no hoist needed. you will end up with approx 2-3 ft sag in this span. there are a lot of charts available if you need them on lineman sites or any engineer can provide them. they also go by the temp at the time of sag and you don't use a stopwatch on triplex. you will not have much pull on the poles at all. you will not have any pull on straight in line pulls. just angles and ends


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## frenchelectrican (Mar 15, 2007)

Garfield.,

As soon Den mention the end and angle pulls it did somehow click in my mind are you aware that with the conductor hook up to the steel post if they are not enforced it can actually bend without serious effort if you get a major storm { strong wind storm or snowstorm } and If you want to keep the overhead spans then it will be a good idea to check the pole manufacter to see if they have enforced verison of that pole you are looking for it.

The last time I have to do that they send me a thicker wall verison with reforced base plate.

Merci,
Marc


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## green light (Oct 12, 2011)

garfield said:


> Basically this is an attempt to save money over boring or sawing parking lot.


 Im sure you have done some research, but are you sure about this. Are these light poles?


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## Fredman (Dec 2, 2008)

Only the wife knows. 

:whistling2:


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## joethemechanic (Sep 21, 2011)

I can't find my lineman's cableman's. It really pizzes me off. People treat my phucking engineering textbooks that cost over 100 bucks each like it's a phucking romance novel.


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## BBQ (Nov 16, 2010)

joethemechanic said:


> I can't find my lineman's cableman's. It really pizzes me off. People treat my phucking engineering textbooks that cost over 100 bucks each like it's a phucking romance novel.


I used to own one, someone 'borrowed' it and now I don't.


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## joethemechanic (Sep 21, 2011)

BBQ said:


> I used to own one, someone 'borrowed' it and now I don't.


Really a good reference book, and not just for electrical. All kinds of good stuff like piking poles, and rigging.

I finally gave up and bought myself a new "Electrical Machines Drives & Power Systems" by Wildi


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## BBQ (Nov 16, 2010)

joethemechanic said:


> Really a good reference book, and not just for electrical. All kinds of good stuff like piking poles, and rigging.


It is. 

For about 5 years I worked at a place where I had to maintain 4160 overhead distribution and that book was really all I had besides just trying to copy what was in place.


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## joethemechanic (Sep 21, 2011)

frenchelectrican said:


> Garfield.,
> 
> As soon Den mention the end and angle pulls it did somehow click in my mind are you aware that with the conductor hook up to the steel post if they are not enforced it can actually bend without serious effort if you get a major storm { strong wind storm or snowstorm } and If you want to keep the overhead spans then it will be a good idea to check the pole manufacter to see if they have enforced verison of that pole you are looking for it.
> 
> ...



There is a very high "Moment" stress in and around the point at which the pole enters the ground.

You end up with what is called an "Abrupt change in section, near "AN AREA OF "HIGH MOMENT" A major structrual engineering no-no



> _Moment of force_ (often just moment) is the tendency of a force to twist or rotate an object; see the article torque for details. This is an important, basic concept in engineering and physics. A moment is valued mathematically as the product of the force and the moment arm. The moment arm is the perpendicular distance from the point of rotation, to the line of action of the force. The moment may be thought of as a measure of the tendency of the force to cause rotation about an imaginary axis through a point.[1] (Note: In mechanical and civil engineering, "moment" and "torque" have different meanings, while in physics they are synonyms. See the discussion in the "torque" article, or the article couple (mechanics).)












And this phucker is pulling on his wrench the wrong way, go figure, but it's a good illistration


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## joethemechanic (Sep 21, 2011)

BBQ said:


> It is.
> 
> For about 5 years I worked at a place where I had to maintain 4160 overhead distribution and that book was really all I had besides just trying to copy what was in place.


A 4160 buss around a plant?


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## BBQ (Nov 16, 2010)

joethemechanic said:


> A 4160 buss around a plant?


No, 4160 outdoors on poles and underground. Many buildings and equipment supplied spread around a large property. The POCO service was 4160 at the property line, we had to handle it from there.

I could handle the overhead work because it was pretty straight forward and basic but when the underground shielded cables needed work I subbed it out.


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## joethemechanic (Sep 21, 2011)

Made it better


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## joethemechanic (Sep 21, 2011)

BBQ said:


> No, 4160 outdoors on poles and underground. Many buildings and equipment supplied spread around a large property. The POCO service was 4160 at the property line, we had to handle it from there.
> 
> I could handle the overhead work because it was pretty straight forward and basic but when the underground shielded cables needed work I subbed it out.



Yeah when conductor spacing gets tight medium and high voltage work gets tricky.

What kind of facility? Manufacturing?


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## BBQ (Nov 16, 2010)

joethemechanic said:


> What kind of facility? Manufacturing?


Sort of, we manufactured vomit.:laughing:

It was an amusement park with 21 adult rides and 12 kiddie rides. along with two large banquet halls, one for 400 people, one for 3000 sitting or about 5000 standing and another 3000 seat dinning hall. 

Rides were 5 HP to 600 HP 208 or 480 depending on the ride.


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## joethemechanic (Sep 21, 2011)

BBQ said:


> Sort of, we manufactured vomit.:laughing:
> 
> It was an amusement park with 21 adult rides and 12 kiddie rides. along with two large banquet halls, one for 400 people, one for 3000 sitting or about 5000 standing and another 3000 seat dinning hall.
> 
> Rides were 5 HP to 600 HP 208 or 480 depending on the ride.


I use to subcontract pump work for sesame place. It was nice clean work. Things went downhill after I did some emergency pumping one night after a big storm on an early summer Friday night

The boss charged them so much he didn't even stop whistling when I told him I submerged a big dual wheel Isuzu diesel utility body doing it.


Six Flags Great Adventure was close and had some big stuff, but we never got in there for some reason, or else they were cheap, I forget


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## wildleg (Apr 12, 2009)

I agree with den. I've only done a tiny bit of overhead work. that's pretty small wire. you can look up the max pulling tension of your wire on the manuf's web site, from what I could tell #6 alum triplex is around 1200. I can't imagine you would put more than 30% of that for tension. you don't want the wire subject to kinking, though, and you have to consider the wind movement as it can damage the cable, and also the function of wind load on your poles and guys. here's a link that might be helpful. I looked up in my linemans & cablemans book, and I couldn't find recommended tensions in there, so I guess it's wire specific, and maybe you could ring up or look up your manuf for recommended stringing tension.

http://www.ergon.com.au/__data/asse...Ver-1-Guidelines-for-Overhead-Line-Design.pdf


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## garfield (Jul 30, 2009)

den said:


> we would go for min 100'-130' on # 6 before we would think about guying it. You can pull this up easy with one guy on a handline. no hoist needed. you will end up with approx 2-3 ft sag in this span. there are a lot of charts available if you need them on lineman sites or any engineer can provide them. they also go by the temp at the time of sag and you don't use a stopwatch on triplex. you will not have much pull on the poles at all. you will not have any pull on straight in line pulls. just angles and ends


 So how far could I go with #8 duplex without a guy wire on a 30 foot steel pole?


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## wildleg (Apr 12, 2009)

you are probably going to have to have an engineer calculate the moment on the pole for you, to make sure your poles will work. He will calculate the worst case scenario based on your location (100mph wind + wire tension based on wire with ice on it, or something like that) and design the poles/bases/anchorbolts and footings accordingly.


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## bobelectric (Feb 24, 2007)

I agree with directional drilling.


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## den (Mar 28, 2009)

garfield said:


> So how far could I go with #8 duplex without a guy wire on a 30 foot steel pole?


 
We never usd steel poles so that would be a manufacturing spec. We used class 5 wood poles which means they were 8-9 in at the top. Our shortest pole used were 30' and our smallest wire was 6 duplex. We maintained 20' clearances on sec wires but would go down to 18 if needed. We never pulled 6 much more than hand tight as the wire is so light a hoist is not needed. When pulling with a hoist, you can tell within one jack when you got the weight of the wire up and was starting to pull tension. I doubt if a steel pole would have any problems with weight and there is no need to actually stretch the wire super tight. I have seen litterly hundreds of trees and rock trucks etc. hit wires and a good pole will take a tremendous impact. Almost always brakes the wire first. I can't find our overhead spec book so I can't quote breaking strength or wire weight but I think #8 duplex would come in somwhere around 20-25' per pound so 100' would really not be much at all


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