Receptacles?

Question

What is the difference between a two slot and a three slot receptacle? Why would one prefer a three slot receptacle?

Answer 1

A three prong receptacle has a third prong for an explicit ground.
A two prong plug may be polarized or not.
If it is polarized then the appliance can theoretically know which wire is electrically neutral.
Sometimes there is still a slight voltage between the neutral wire and the true ground potential. (corrosion, poor workmanship etc.)
If there is any wire accidentally touching a metal case then the case may become electrified.
If it is properly grounded then there is not a problem because if it is a live wire then the fuse will blow. If it is a neutral wire then the neutral will be pulled to the ground potential. It is far less likely that anyone would get shocked even if the wiring was all screwed up.
A grounded chassis in electronics can provide a better reference potential for the circuitry and eliminate hum.

Answer 2

A three slot has a ground whereas the two slot does not or uses the negative as the ground also. which means, the chance of shock exist and lightening can travel through the system and destroy any devices connected to this power teminal.
Grounded devices create a path to Earth for lightening ( which wants to go to Earth by its very nature).
I do not think you'll buy a two slot replacement today anyway, but if your wiring uses this type throughout the structure then it is definitely time to upgrade to a newer Panel Box that permits a separate ground terminal - hence install three terminal receptacles / devices ( remember you other devices connected are not grounded propperly either).

Answer 3

Because the third slot is used as a safty measure...it is the ground slot. the ground slot is used as a protective device to help avoid from any shock or electric overloads.