How do you wire a Buzz-In Door System?

The third wire provides a ground to ensure safety. Older houses, pre1950 probably have the two wire system, some even have tube and knob.

Coclusion is not a word.

Garage door openers do not get "wired." They are sold with a standard 3-prong, 120VAC plug that is about two-feet long and plugs into a 15A, 120VAC outlet -- next to the location where the opener is...

Yes. Whatever you ate will float around in your system until your body gets rid of it. For MDMA it'll be detectable for 2-7 days or so.

I assume you mean hot, neutral and ground. The answer is simple...the advantage is life or death in a home wiring situation. The only true job of electricity is to seek ground and it will find it...