Cable Clearance Calculations

[Natfuelbilll]

Have you found it necessary to perform cable clearance calculations as shown in this document?

http://ecmweb.com/content/simple-calculations-cable-pulling.

 

[jumper]

I am just a grunt, so no, I have never did those calcs. Boss or EE may have.

Only thing I really recognized was the part about jam ratio.

Article said this:

Use the following formula to determine the likelihood of jamming. Use the inside diameter of the raceway and the outside diameter of the individual conductor:

1.05 x (D ÷ d)

The constant 1.05 factor is a reflection of the fact that bends are actually oval in the sectional view.

• If the value is less than 2.5, you will not have a jamming problem.


• If the value is less than 3.0 but greater than 2.8, jamming is very possible.


• If the value is greater than 3.0, you won't have a jamming problem.


Note: Keep away from jam ratios of 2.8 to 3.2 for Type MV extruded dielectric power cables.

Using the values for inside diameter of the raceway and the outside diameter of the individual conductor from the example, you get the following value:

1.05 x (D ÷ d)
1.05 x (5.07 in. ÷ 1.60 in.)
= 3.33

Because this calculation results in a number greater than 3.0, you probably won't have a jamming problem.

Which kinda matches the NEC Informational Notes for Table 1, Chapter 9:

Informational Note No. 1: Table 1 is based on common
conditions of proper cabling and alignment of conductors
where the length of the pull and the number of bends are
within reasonable limits. It should be recognized that, for
certain conditions, a larger size conduit or a lesser conduit
fill should be considered.

Informational Note No. 2: When pulling three conductors
or cables into a raceway, if the ratio of the raceway (inside
diameter) to the conductor or cable (outside diameter) is
between 2.8 and 3.2, jamming can occur. While jamming
can occur when pulling four or more conductors or cables
into a raceway, the probability is very low.

 

[jumper]

Before someone asks, yes I know about conduit fill also, but everyone has did that calc.

 

[don_resqcapt19]

I have never heard of the "clearance" calculation before. I have often done the jamming, pulling tension and sidewall pressure calculations.