Type AC and MC Cable exception added to Table 310.16 Calculator

I spent most of the day adding Section 310.15(B)(2)(a) Exception No. 5 to the calculator program. This is where the special 60 per cent derating applies to MC and AC cables. Ambient derating still applies but the over three current carrying conductor derating does not apply as long as there are less than 20 current carrying conductors and each cable has no more than 3 current carrying conductors. There is one problem, though. The Code does not specify 90 degree insulation for the Type MC cable conductors but does so for the Type AC conductors.

Here is the exception:
310.15(B)(2)(a)
Exception No. 5: Adjustment factors shall not apply to
Type AC cable or to Type MC cable without an overall
outer jacket under the following conditions:
(1) Each cable has not more than three current-carrying
conductors.
(2) The conductors are 12 AWG copper.
(3) Not more than 20 current-carrying conductors are
bundled, stacked, or supported on “bridle rings.”
A 60 percent adjustment factor shall be applied where the
current-carrying conductors in these cables that are
stacked or bundled longer than 600 mm (24 in.) without
maintaining spacing exceeds 20.