Bundling Cables Upsized for Voltage Drop

[Limbty]

The inspector at our job site called us on bundling some home runs going through a wall. The runs are supported by UL listed j-hooks suspended by all-thread. Due to the length of these circuits, we’ve had to upsize our home runs up to 6 awg for 20A. In the 2020 NEC, it says in 310.15 (C) (1) (d) (1-4),
(d) Adjustment factors shall not apply to Type AC Cable or to Type MC Cable under the following conditions:
(1) The cables do not have an overall outer jacket.
(2) Each cable has not more than three current-carrying conductors.
(3) The conductors are 12awg copper.
(4) Not more than 20 current-carrying conductors are installed without maintaining spacing, are stacked, or are supported on “bridle rings.”
We meet the requirements of 1 and 2. The exception for 4 says for more than 20 current-carrying conductors longer than 24 in. a 60% adjustment factor shall be applied. With 1,2 and 4 met, that leaves 3 up to question. It’s not 12awg because it’s adjusted to voltage drop. Is there another code reference I am missing? Is bundling in our case permitted?

 

[wwhitney]

Your #6 AWG has a 90C ampacity of 75A. Even if you have 500 CCCs, the derating factor is 0.35 at worst. 75 * 0.35 = 26A, which is more than 20A. So what's the problem?

Basically since you've upsized the conductors so much for voltage drop, that takes care of any bundling issues you might conceivably have. Upsizing gives you both benefits at once--higher base ampacity for derating, and lower voltage drop.

As to your question, if you're using a size other than #12 AWG, that section doesn't apply.

Cheers, Wayne