Max Pullbox Spacing for 500kcmil Feeder Pull

[rachael10055]

I am trying to determine if there is a standard or set of official rules for the distance a run can go between pullboxes if the designer is not actually completing pull calculations until post IFC.

The parameters are 3x500kcmil 1/C 2.4kV Okonite cables run in 4" PVC that transitions to RTRC for the final stub up. The full cable length from the disconnect to the feed point is approx 1800' with two manholes within that length. Bends are all fairly large but I can't determine exact degrees of each based on the info provided by the designer. I know there are no more than 270deg in each run between current boxes. There is one 90 (24" radius min) at the end of the pull (feed point) where the conduit comes up from the underground ductbank. No information was provided for any vertical transitions within the runs.

The question is basically, should they add more pullboxes and if so, is there documentation I can provide to them to require it?

 

[winnie]

The NEC doesn't have any specific limit for distance between pull points.

You have to do the pull calculations to ensure that the pulling tension will be less than the documented maximum pulling tension for the cable.

There is also the practical matter of how long the available cable runs are.

-Jon

 

[tom baker]

MV is not my area, but from trolling this site, I would suggest that you get a software program and calculate the pull to see if the max pulling tension will be exceeded.
What is a TES discipline manager?

 

[Hv&Lv]

I am trying to determine if there is a standard or set of official rules for the distance a run can go between pullboxes if the designer is not actually completing pull calculations until post IFC.

The parameters are 3x500kcmil 1/C 2.4kV Okonite cables run in 4" PVC that transitions to RTRC for the final stub up. The full cable length from the disconnect to the feed point is approx 1800' with two manholes within that length. Bends are all fairly large but I can't determine exact degrees of each based on the info provided by the designer. I know there are no more than 270deg in each run between current boxes. There is one 90 (24" radius min) at the end of the pull (feed point) where the conduit comes up from the underground ductbank. No information was provided for any vertical transitions within the runs.

The question is basically, should they add more pullboxes and if so, is there documentation I can provide to them to require it?

I wouldn’t be scared of 600’ runs on that pull if they were straight(ish) but 600’ pulls with 270 degrees of bend would bother me even without the calculations. The 24” bend at the end may be pushing or breaking bending radius limits for MV cable also. (12 times)
If u you or use a calculation software make sure to include a negative number on the reel tension if you have guys pushing.

 

[sameguy]

Make sure your boxes are sized correctly and set them to aide your pull.

 

[don_resqcapt19]

... The 24” bend at the end may be pushing or breaking bending radius limits for MV cable also. (12 times)
If u you or use a calculation software make sure to include a negative number on the reel tension if you have guys pushing.

Even if the bend radius is not an issue for the cable being used, it may be when you look at the sidewall pressure calculation, especially where the bend is at the pulling end of the run. The sidewall pressure goes down as you increase the bending radius.

 

[Hv&Lv]

Even if the bend radius is not an issue for the cable being used, it may be when you look at the sidewall pressure calculation, especially where the bend is at the pulling end of the run. The sidewall pressure goes down as you increase the bending radius.

Correct. I wouldn’t pull through that tight bend.

 

[Julius Right]

The maximum delivery length is not a problem.
See Okonite Engineering Handbook /2018 pg.40 Maximum Pulling Tension. [1*500 MCM copper 2.4 kV not-armoured weight it is 2.05 lbs/ft].
In my opinion no more than 180o it has to be at both ends.
In my opinion also, the maximum 500 ft has to be between pulling points [distance between adjacent manholes] if the cables are well lubricated, and I think the minimum bend radius has to be 5.5 ft

 

[Julius Right]

Practical our experience the pulling distance it is not more than 150 fts. including equivalent of two 90° bends.

 

[don_resqcapt19]

Practical our experience the pulling distance it is not more than 150 fts. including equivalent of two 90° bends.

Industrial cable pulls are rarely that short between pull points. You need to look at the pulling calculations and pull with the least number of pull points that you can without damaging the cable. There is much more risk of cable damage as you pull in and out of a pull point than within the pull itself as long as you do the pulling calculations.

 

[Julius Right]

I agree with you don_resqcapt19.I referred to power station. So, here the standard is elevated.
There are many ways to pull cables. First, the duct has to be clean and empty and full of lubricant. You may use grips or direct pull the conductors. You may use mechanical pulling devices or pulling by hands. You may provide a dynamometer or not and other ways. You may pull all three phases at once or pull as single phases.
Anyway, I think the designer should work together with executor in order to find the solution.

 

[Julius Right]

If someone intends to calculate the actual cable run pull force I’ll recommend:
Power Plant Electrical Reference Series volume 4 Wire and Cable EPRI-EL-5036-V4
https://www.amazon.com/Power-Plant-Electrical-Reference-Vol/dp/0803350031
page 71

 

[steve66]

My 2 cents: I know we have specified 5" or even 6" conduit for 500KCM 5KV cables in the past. So you might also want to do a conduit fill calculation using the actual cable diameter.

 

[don_resqcapt19]

...You may pull all three phases at once or pull as single phases.
...

I would never ever consider pulling conductors or cables one at a time in a common raceway. Why too much risk of the friction from the second and third pulls cutting into the insulation of the conductor pulled in first.