Can Class 2 lighting control wire share a conduit with 120 volt conductors?

No. Section 725.136(A) prohibits Class 2 conductors from occupying the same raceway or enclosure as electric light and power conductors unless a listed exception applies.

Does shielded control cable change the separation rule?

No. Shielding addresses electrical noise, not the NEC separation requirement. Section 725.136(A) makes no allowance for shielded Class 2 cable.

How do I legally run control wiring in the same pipe as the switch leg?

Reclassify the circuit as Class 1 under 725.130(B). Remove the Class 2 marking from the supply, use Chapter 3 wiring methods with 600 volt rated conductors, and the circuits may then share the raceway under 300.3(C)(1).

Can I pull shielded low voltage lighting control wiring and the switch leg in the same conduit?

Not as a Class 2 circuit. Section 725.136(A) of the NEC states that Class 2 and Class 3 conductors shall not be placed in any cable, cable tray, compartment, enclosure, manhole, outlet box, device box, raceway, or similar fitting with conductors of electric light, power, Class 1, non-power-limited fire alarm, or medium power network-powered broadband communications circuits. A 120 or 277 volt switch leg is a power conductor. Shielding on the control cable does not change that. The shield is a noise mitigation feature and the code does not recognize it as a substitute for separation.

The exception you actually want: reclassification

Section 725.130(B) lets you reclassify a Class 2 or Class 3 circuit as a Class 1 circuit. When you do, three things follow. First, you strip the Class 2 markings off the power supply so nobody downstream treats it as power limited. Second, you install the conductors using Chapter 3 wiring methods, which means the conductors themselves must be Chapter 3 conductors with a 600 volt insulation rating, not the little 300 volt jacketed control cable off the reel. Third, the reclassified circuit is then permitted to occupy the same raceway with the power conductors under 300.3(C)(1), because now everything in the pipe is rated 600 volts.

In practice this means running 18 AWG or 16 AWG conductors that meet 725.49(B), or more commonly just pulling 14 AWG THHN for the control pair. Once the circuit is reclassified you also inherit the Class 1 overcurrent rules in 725.43 and the derating obligations of 310.15(C)(1) once the raceway carries more than three current-carrying conductors.

The other exceptions in 725.136

Section 725.136(B) allows the two to share an enclosure where they are separated by a barrier. Section 725.136(D) permits Class 2 and power conductors in the same enclosure, cable, or raceway where they are functionally associated, meaning the Class 2 circuit is introduced solely to connect to the equipment that the power conductors serve, and specific separation or listing conditions are met. A dimming ballast whip is the classic example. A homerun from a lighting control panel to a room controller is not functionally associated in that sense once it passes other equipment.

What most crews do

Run a separate 1/2 inch or 3/4 inch raceway for the control pair. It costs less than reclassifying, keeps the noise floor down, and leaves you free to use standard listed control cable. If the run is short and the conduit is already there, reclassifying to Class 1 and pulling 14 AWG THHN for the control conductors is clean and defensible. Whichever you choose, document it, because an inspector who sees purple control cable in a pipe with a switch leg will fail it on 725.136(A) and will not know you intended to reclassify.

Field takeaway

Class 2 control cable and a line voltage switch leg do not share a conduit. Either pull a separate raceway or reclassify the control circuit under 725.130(B) and use 600 volt conductors and Chapter 3 methods.