UL 508A vs. NEC

[petersonra]

Back to the original bigger picture;
If a control panel is UL listed (or listed by any other NRTL), the NEC applies only to the installation of the panel, not the internal components that were part of the UL listing. So when UL has different rules, such as wire sizing, it trumps the NEC because once that panel is listed, the installer can connect it as long as HIS connections meet NEC rules.

So to your 10ft tap rule, UL would apply in the construction of the panel at your shop, not the NEC. But there is the same requirement in UL 508A to address that and although worded differently, the net result is the same as the NEC. You can do it, but with rules.
For example:

UL 508A, Section 31.4
The ampacity of the tap conductors, the internal
conductors to the individual loads, shall be:
a. Not less than 1/3 the ampacity of the branch circuit conductor,
calculated as in 28.3.3; or
b. Not less than 1/10 the ampere rating of the branch circuit protection
for the group for each motor circuit provided with a
manual motor controller marked “Suitable as tap conductor
protection in group installations” and complies with the
Standard for Industrial Control Equipment, UL 508.
The conductors on the load side of the manual motor
controller shall have an ampacity not less than calculated in
28.3.2.

Bottom line: IF you have UL listed panel, UL rules apply on the inside; NEC on the outside and coming in. If you have a-bunch-o-parts-in-a-box control panel, the NEC would apply through and through. But many states have rules that say any more than "x" parts-in-a-box will have an overall NRTL listing anyway. The NEC as a national document however stops short of the NRTL listing as a requirement, it is a suggestion.

Section 31.4 only applies to motor group wiring, not branch circuits in general in my versions of UL508a. maybe mine is old.

 

[Jraef]

Section 31.4 only applies to motor group wiring, not branch circuits in general in my versions of UL508a. maybe mine is old.

No, I agree, it does only apply to motor branch circuits. But I was just pointing out that there are some requirements addressing this in UL. The OP had implied that he saw nothing about it and never specified the types of control panels or circuits within them that he was referring to.