[Daniel_Newby]

Read the actual laws. They generally require a licensed PE for any task that (1) requires engineering or technical knowledge to complete correctly, and (2) has an influence on life, health, or property, no matter how trivial. It's like requiring personal trainers to be board-certified cardiologists. Naturally everybody ignores this, and compliance consists of not drawing the attention of the state engineering board.

Electricians follow a handbook rather than derive results from general knowledge, so the PE laws don't apply. As long as the electrical code handbook allows it, they can do it. Possibly at enormous expense, which is why you want a power engineer to plan your factory wiring.

[assemble]

The laws vary from state to state. I'm not going to read them all. Here are the laws in my state: http://www.kansas.gov/ksbtp/statutes.html Specifically pertaining specifically to who does or doesn't need a license: http://www.kansas.gov/ksbtp/74-7035.pdf

I've always thought a phlebotomist is similar to a licensed electrician. (Assuming an MD is similar to a PE)