Chapter 9 Table 1

[wbalsam1]

• A cable is treated as 1 conductor and can take up to as much as 53% of the raceway.
• One conductor can also take up the same cross-sectional area of the raceway, namely 53%.
• Two conductors can take up to 31%
• Three or more can take up to 40%
• In a nipple (less than 24" in length) one or more conductors can take up to 60%

Here's my question: Why 31% for 2 conductors which is less cross-sectional area than 40% for 3? In other words, it seems like for 2 conductors you must use less than for 3.

 

[bphgravity]

3 or more conductors tend to pull "flat" through a raceway. 2 conductors tend to twist and form a double-helix. Think "DNA". This double helix configuration adds tension to the pull thus requires more space than pulls of three coductors or more.

 

[wbalsam1]

3 or more conductors tend to pull "flat" through a raceway. 2 conductors tend to twist and form a double-helix. Think "DNA". This double helix configuration adds tension to the pull thus requires more space than pulls of three coductors or more.

Thanks. I've wondered that for years...now I know. :smile:

 

[Pierre C Belarge]

Take a look at the FPN that follows the table, it will give you an answer as to why the table has been designed as such.

 

[C3PO]

I think it has to do with what is called the "jam ratio"

 

[LarryFine]

I think it has to do with what is called the "jam ratio"

I thought that had something to do with making PBJ sandwiches.

 

[Smart $]

Why 31% for 2 conductors which is less cross-sectional area than 40% for 3? In other words, it seems like for 2 conductors you must use less than for 3.

Looking at it from a geometrical standpoint helps to understand why...