Distance between Manholes - Is there a NEC Requirement

[Carvrboy]

Our Estimator is planning to offer a credit for an Underground installation that includes UG conduit & manholes, per plans/drawings. His plan is to bore approximately 1200' and pull the 12-kv conductors - through the bored conduit(s) from the first/ beginning manhole to the end/last manhole. The 1200' would be a straight pull. Our boss thinks there is a maximum distance allowed for the Underground conduit and a manhole or manholes must be installed, per the NEC. Oh yes, we are in the 2017 NEC cycle, in case that makes a difference. I haven't found anything in the 2017 NEC that would place a distance between manholes for an UG conduit installation. I did ask our Estimator to check with the cable manufacturer to see if there was any limitations on the conductors for that type of pull.

Can anyone come up with a NEC reference limiting the 1200' pull and placing manholes in the UG conduit installation?
Thanks,

 

[rnatalie]

To my knowledge, there is no such requirement. Manholes have requirements when they are used, but their spacing is determined by other practical considerations (bend limits, how long of a single conductor you can get, etc...) rather than any specific length.

 

[480sparky]

I reckon the maximum would be (roughly) around 25,000 miles / 40,000 kilometers, the circumference of the earth. Any more and you'd be over the 360° of bends allowed.

 

[tom baker]

And you are also limited by the max pulling tension of the cable, check with mfg and there is software available to calculate

 

[Carultch]

I reckon the maximum would be (roughly) around 25,000 miles / 40,000 kilometers, the circumference of the earth. Any more and you'd be over the 360° of bends allowed.

You will exceed the factory length of your cable, before the Earth's curvature contributes even a hundredth of a degree. The curvature in local terrain is going to impact the bend accumulation a lot more than the global curvature.

Splicing has to occur in an access point, so the spool length will be the important limit on pull point spacing.