It's the common practice... particularly in retrofits.
Not uncommonly, the LV DC circuits need shielding, too.
This practical need is not embedded in the NEC -- just in the laws of physics.
You don't want your DC driving currents to pick up 60Hz ripple. While it won't burn the house down, any such ripple would degrade the quality of the LED output.
[ Which reminds me of the Swiss Railway gambit. Retail power consumers were tapping their traction power so as to power Edison lamps -- going back a century ago.
So, very early in, the railroads converted over to 50/3 Hz power. Such a low frequency caused resistence driven illumination to strobe up and down at that very annoying frequency. It also made it obvious when a retail user was tapping in to the traction power grid. (This issue probably popped up the day after urban trolleys were running on juice.)]
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Unlike Edison lamps, LEDs are going to react at solid state speed to any swing in voltage.
Last edited by Tesla; 02/15/14 03:33 AM.
