@skywatch do Fluke meters work unattended in enclosed cabinets or walls, using varistors for power supply 24/7?
As I've said I prefer using a better power supplies with built-in over-voltage protection. As for how it is achieved without a varistor you can find plenty information by yourself using google.
If anyone else ends up here like I did.
To drive the DIM Control pin without pulling from Vdd, try this.
This will keep the micro isolated. This assumes that you use a dual optoisolator, and that the CTR is the same. To ensure they ARE equally matched, you can buy the more expensive IL300 or LOC110 - built especially for this purpose.
Also do note: if you are going to make a DUAL dimmer, then do NOT connect the 'GND' between dimmer A and dimmer B. They must be separate.