NEC Table 400.5

[erickench]

Okay, the above table contains the percentage values for adjusting the ampacity of conductors that are bundled together at more than three conductors at a time. This table is supposedly applied to NEC Tables 400.5(A) and 400.5(B). Now both of these two tables have columns that separate the ampacity values into groups according to temperature and number of conductors. Table 400.5(B) is easy enough to use because all we have to do is determine the temperature. But Table 400.5(A) has two columns, 'A' and 'B', dividing the ampacity values according to the number of conductors. My question is this:

Which column are the adjusting factors of Table 400.5 applied to in Table 400.5(A)?

My money is on column 'A' because it's three conductors and not two. You see the NEC does not specifically say which column to apply the adjustment factors to.

 

[wireguru]

400.5 is ampacity of flexible cords, not bundles of conductors.

 

[erickench]

400.5 is ampacity of flexible cords, not bundles of conductors.

Even if it is ampacity of flexible cords they still contain bundles of conductors that have to be adjusted. The question still remains because one table is supposed to apply to the other. It's a matter of which column. Here's my thinking:

Assume we have 4-6 conductors in a flexible cord. The adjustment factor is 80%. If we apply this 80% to column B for an 18 AWG, the equation would be .8x10=8A which is higher than the column A ampacity of 7A for the same wire gauge. Column A is for three conductor flexible cords. It would not be correct if the ampacity of a 4-6 conductor flexible cord is higher than that of a three conductor flexible cord.:grin:

 

[wireguru]

Even if it is ampacity of flexible cords they still contain bundles of conductors that have to be adjusted. The question still remains because one table is supposed to apply to the other. It's a matter of which column. Here's my thinking:

Assume we have 4-6 conductors in a flexible cord. The adjustment factor is 80%. If we apply this 80% to column B for an 18 AWG, the equation would be .8x10=8A which is higher than the column A ampacity of 7A for the same wire gauge. Column A is for three conductor flexible cords. It would not be correct if the ampacity of a 4-6 conductor flexible cord is higher than that of a three conductor flexible cord.:grin:

i thought you take the derating in 400.5 from column A in 400.5(a) no?

 

[erickench]

Yes you do Wireguru. The point I'm making is that the NEC does not specify which column in Table 400.5(A) is to be used. I am simply making a case that column A, the three conductor cords, are used instead of column B, the two conductor cords.

 

[wireguru]

Yes you do Wireguru. The point I'm making is that the NEC does not specify which column in Table 400.5(A) is to be used. I am simply making a case that column A, the three conductor cords, are used instead of column B, the two conductor cords.

yeah, i just looked at it and they dont specify what column to use. wierd.

 

[zbang]

I think it does specify the column, but it's not exactly straightforward--
(looking at 2005, since that's the one I grabbed off the shelf)

As I read it, you apply the derating from table 400.5 to column A in table 400.5(A).

Why? Because the text at the end of section 400.5 (A) says "Where the number of CCC exceeds three, [...] shall be reduced from the 3-conductor rating" and the 3-conductor rating is in column A of table 400.5(A).

Likewise, the note below table 400.5(A) says "allowable currents under Column B apply to 2-conductor cord [...] only 2 conductors are current carrying", so the derating in the text of section 400.5 (A) wouldn't apply.

Of course, they could just come out and say "use Column A"....

 

[erickench]

Yea you're right zbang. It say's that in the 2008 NEC too.