Derating wire exception in 2008 NEC code

[Tainted]

In NYC we are stuck with 2008 NEC with amendments.

In the updated code 310.15(B)(2)(a) exception it says "Adjustment factors shall not apply to conductors in raceways
having a length not exceeding 600 mm (24 in.)."

However in the 2008 NEC it does not say that. It only gives the exception for nipples and not raceways specifically: "Exception No. 3: Derating factors shall not apply to conductors in nipples having a length not exceeding 600 mm (24 in.)."

If I'm under the 2008 NEC, does this mean I still have to derate wires that are less than 24 inches in the raceway?

 

[infinity]

No. A nipple is a short section of raceway.

 

[Tainted]

No. A nipple is a short section of raceway.

I've always thought a nipple and a raceway are two different things.

What if the wire is less than 24 inches in a wireway? a wireway is not defined as a nipple?

 

[infinity]

Wireways have a different set of rules. Derating doesn't apply until you have more than 30 CCC's at a cross section.

 

[Tainted]

Wireways have a different set of rules. Derating doesn't apply until you have more than 30 CCC's at a cross section.

What if the wire is less than 24 inches in a wireway under the 2008 NEC?

 

[infinity]

What if the wire is less than 24 inches in a wireway under the 2008 NEC?

Once you hit 30 CCC's at any cross section it doesn't matter how long the conductors are. Below is from the 2008 NEC, although implied in earlier versions the words "at any cross section of the wireway" weren't added until the 2014 NEC. Some have argued that 310.15(A)(2)Exception can make derating moot.

376.22 Number of Conductors and Ampacity. The number of conductors and their ampacity shall comply with 376.22(A) and (B).
(A) Cross-Sectional Areas of Wireway. The sum of the cross-sectional areas of all contained conductors at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway.
(B) Adjustment Factors.
The adjustment factors 310.15(B)(2)(a) shall be applied only where the number of in current-carrying conductors, including neutral conductors
classified as current-carrying under the provisions of 310.15(B)(4), exceeds 30. Conductors for signaling circuits or controller conductors between a motor and its starter and used only for starting duty shall not be considered as current-carrying conductors.

 

[Dennis Alwon]

Wireways have a different set of rules. Derating doesn't apply until you have more than 30 CCC's at a cross section.

The confusion may be that a wireway is considered a raceway, however, as Infinity stated it has different rules

Metal Wireways.
Sheet metal troughs with hinged or removable covers for housing and protecting electrical wires and cable and in which conductors are laid in place after the raceway has been installed as a complete system.

376.22 Number of Conductors and Ampacity.

The number of conductors or cables and their ampacity shall comply with 376.22(A) and (B).
(A) Cross-Sectional Areas of Wireway.

The sum of the cross-sectional areas of all contained conductors and cables at any cross section of a wireway shall not exceed 20 percent of the interior cross-sectional area of the wireway.

(B) Adjustment Factors.

The adjustment factors in 310.15⁠(B)⁠(3)⁠(a) shall be applied only where the number of current-carrying conductors, including neutral conductors classified as current-carrying under the provisions of 310.15(B)(5), exceeds 30 at any cross section of the wireway. Conductors for signaling circuits or controller conductors between a motor and its starter and used only for starting duty shall not be considered as current-carrying conductors.