duplex = 2. Duples outlet in the US.
There was a piece of stamped brass connecting the circular holes internally.
Mounting would be a U shaped metal around the back of the outlet. Internally, the brass piece and the U shaped piece was just friction. The outlet had screws that put it together,
One of the grounds would come undone based two cord plugged in wiggling the other one.
The two screws on the left goes to the smaller height square contact and they can be separated so one goes to the top one and one goes to the bottom. This is hot. Usually brass.
the one on the right is our neutral. Usually chrome. Same idea.
The one at -45 degrees on the right is ground and usually green. The metal box, if used, is not supposed to be grounded by the mounting screw, but the metal box, if used, needs to be grounded.
Take an RFI line filter such as this one. e.g. corcom
usually used in switching power supplies. leakage current is 0.5mA max.
The caps on the load side makes a nice little voltage divider with some of the leakage current.
take the ground away on the right and you have a 1/2 the line voltage voltage source.
So, that stray "ground" has just raised the ground potential of a computer chassis by 60 V if the bond to real earth goes away.
Now lets suppose you have a parallel printer and it;s plugged into a real outlet with a real zero volt ground.
So, our printer sees 63vac+3.5VDC and it isn't happy.
I hope you followed. it happened about 3 or 4 times to me at work.
The first place it happened was an outlet strip.
here
is an outlet strip/surge suppressor. That's 3 duplex receptacles and it's what the USA has in our walls. We usually have a duplex receptacle about every 3 meters or so or maybe one on each wall in a bedroom.
If the ground lets go at 12 and 21, and either outlet has a switching power supply and something is plugged into 11, 21, 31 or 32 you have a problem.
I had a mechanical problem with 12's ground and 22's ground.
The 11 positon is top left.
I have an open living room/dinimg room, so the living room is open to a hallway on one side and the dining room on the other. Typically you have one duplex receptacle on each wall. in a bedroom. The living room gets a switched receptacle for a floor lamp. The dining room may have a chandelier. A bedroom has a ceiling light, but I;ve seen some bedrooms eles ewhere that have had switched outlets.