Pull box for underground conduits

[Leo Li]

Hello Sir, regarding underground conduits pull box, as my constuction experience the underground box will be added once the total conduits bend exceed three 90 degree bend or total exceed 270 degree then pull box will be added. But when I comment this to our design firm as below but they fedback " COMMENT IS NOT ACCEPTED: THERE WILL BE 270 DEGREES BEND. US NATIONAL ELECTRICAL CODE ALLOWS 360 DEGREES BEND." is this true? I didn't find this in NEC code or I missing something. Thanks !

 

[tom baker]

NEC limit is 360 degrees. Often specs and good practice limit to 270 degrees. I don’t have to look up section as most know 360 degrees, did you look in Article 300?

 

[Leo Li]

NEC limit is 360 degrees. Often specs and good practice limit to 270 degrees. I don’t have to look up section as most know 360 degrees, did you look in Article 300?

Thank you! Yes, I do find limit is 360 degree in article 300 but I am concerning it is very difficult o pull cable if bend is 360 degree for those large size cables.

 

[Fred B]

Thank you! Yes, I do find limit is 360 degree in article 300 but I am concerning it is very difficult o pull cable if bend is 360 degree for those large size cables.

If you're not pulling, don't worry about it, 360 code compliant. Likely contractor or client is being "cheap" these traffic rated boxes are not cheap (it looks like parking lot being crossed).

 

[ptonsparky]

Thank you! Yes, I do find limit is 360 degree in article 300 but I am concerning it is very difficult o pull cable if bend is 360 degree for those large size cables.

That is why good practice may limit it to 270.

 

[don_resqcapt19]

Thank you! Yes, I do find limit is 360 degree in article 300 but I am concerning it is very difficult o pull cable if bend is 360 degree for those large size cables.

It really is not that difficult to pull large conductors through 360° of bend (or even more than that) if you know what you are doing and have the right equipment.

Someone does need to do a pulling calculation for longer, large conductor pulls, even with 270 degrees of total bend to be sure that the cable will not be damaged in the pull. The typical limiting factor is the side wall pressure on the conductor insulation as the conductors are pulled around the bends. That can be corrected by using a larger radius bend or reducing the required pulling force by reducing the number of bends.

You really should do a pulling calculation at the design stage to determine the layout of the pull points and the number of bends that can be used. On long long runs, it is my opinion that handing the conductors at pull boxes, when you have to pull it out and feed it back in is more likely to damage the conductors than is pulling around an additional bend.

 

[Leo Li]

Thank you! Yes, I do find limit is 360 degree in article 300 but I am concerning it is very difficult o pull cable if bend is 360 degree for those large size cables.

Thanjs! So how is those equipment metal enclosure ground such as boiler, Chiller etc.; ? Also through

It really is not that difficult to pull large conductors through 360° of bend (or even more than that) if you know what you are doing and have the right equipment.

Someone does need to do a pulling calculation for longer, large conductor pulls, even with 270 degrees of total bend to be sure that the cable will not be damaged in the pull. The typical limiting factor is the side wall pressure on the conductor insulation as the conductors are pulled around the bends. That can be corrected by using a larger radius bend or reducing the required pulling force by reducing the number of bends.

You really should do a pulling calculation at the design stage to determine the layout of the pull points and the number of bends that can be used. On long long runs, it is my opinion that handing the conductors at pull boxes, when you have to pull it out and feed it back in is more likely to damage the conductors than is pulling around an additional bend.

Thank you very good reply Sir!