Conduit bend radius

[anbm]

Does NEC address min. and max. conduit bend radius based on certain conduit size and type?
If so, how to calculate this radius for duct bank turn with multiple ducts? Is it civil engineer's job?

 

[Carultch]

There is no max bend radius. There is a standard for minimum bend radius. See tables in Chapter 9 that specify this information. The numbers given refer to the centerline, if you plan on using this information to draw it to scale.

 

[don_resqcapt19]

The pulling calculation often influences the choice of what radius is used. The use of larger radius may be required to limit damage to the conductors as a result of the sidewall pressure that is a function of the pulling tension and the bend radius.

 

[infinity]

Does NEC address min. and max. conduit bend radius based on certain conduit size and type?
If so, how to calculate this radius for duct bank turn with multiple ducts? Is it civil engineer's job?

When you say multiple ducts are you trying to calculate for concentric bends?

 

[anbm]

When you say multiple ducts are you trying to calculate for concentric bends?

yes

 

[JoeStillman]

Here is a good resource for installing PVC ducts. It says in Appendix A you can field bend a radius of as little as 35' using 4" ducts. Use factory elbows for smaller radii.

http://www.heritageplastics.com/wp-content/uploads/2016/08/NEMA-TCB-2-2017-Watermarked.pdf