In my post I did not exclude the possibility of making mains connected equipment. It is done all the time!! Consider X10 equipment for one example. However if it is done you just need to think about the issues involved and thus the points I raised in my previous post.

Goodness a friend of mine worked on a neat little appliance monitor module that was line connected and direct powered! It was a lump that plugged into a electrical outlet and then your lamp, refrigerator, etc plugged into the lump. This device monitored electrical usage and provided average cost per day display of the electrical power consumption. It even had LCD display and several buttons controlled by a microcontroller. His design considerations included UL listed components and a completely double insulated packaging with no metalic interface from the device that was acessable to the user once the lump was plugged into the wall (this device had a power plug on the back so it mounted similar to a wall wart powersupply).

Michael Karas