The inspector wanted Ground Down at the Hospital...
View attachment 855410
The provided photo show the hot lead on the right, the ground on the left. (This is also a 20 amp rated industrial receptacle identified by the T slot on the left) The ground side of a wall receptacle is also the larger of the two female receptacles on the wall plug in receptacle. The bottom hole on the receptacle is round and is the neutral safety. The round male protrusion on the plug in electrical cable is longer than the two other spade plugs. The ground is the larger of the two spade connectors on the plug.
Now I will let a electrical engineer explain why the round hole is on a wall receptacle.
Michael Craft
“Electrical Engineer at University of Dayton Research Institute.”
Why are there 3 wires in electricity plugs while neutral and ground wires are fundamentally the same?
With all due respect, most of the responses don’t really answer the OP’s question.
It all starts with the fact we want the metal chassis of a device or appliance to be connected to earth ground. Connecting the chassis to earth ground protects the user from an electric shock if there is a fault inside the device.
Now I know what you’re thinking: “The neutral is connected to earth ground back at the circuit breaker box. So why not connect the neutral to the device’s metal chassis?”
So let’s say you have a two-wire system (just hot and neutral) and you connect the neutral to the chassis. User is protected from shock, right? Not necessarily.
Let’s first assume you are “grounded.” This happens all the time. Perhaps you’re standing barefoot on concrete. Or touching a metal sink.
If there’s a break in the neutral line and you happen to be touching the device’s metal chassis, electric current will flow:
- from the circuit breaker box,
- through the hot conductor inside the walls of your house,
- to the wall receptacle,
- through the hot wire in the device’s power cord,
- through the electronics inside appliance,
- into the chassis,
- through you,
- into the earth (we are again assuming you are grounded),
- through the earth,
- to the copper rod next to the circuit breaker panel,
- through the copper wire (that connects between the rod and the neutral bus bar inside the circuit breaker panel),
- to the neutral bus bar inside the circuit breaker panel.
And the circuit is now completed. You will get zapped.
“I understand. But come on… how often does a break occur in the neutral line? Sounds like a very rare occurrence.”
A “break” in the neutral line occurs a lot more often than you think. In fact, a “temporary” break in the neutral happens all the time. Think about it… when you stick a 2-pronged plug into a receptacle, do you think the neutral always makes contact first? Nope - the hot and neutral prongs are the same length. So when you plug something into an outlet, 50% of the time the hot makes contact before the neutral! This means there will be a time span (typically a few tens of milliseconds) where only the hot is making contact at the plug/receptacle, and not the neutral. If the neutral were connected to the chassis, and you happened to be touching the chassis while sticking the plug in the receptacle, you’d get zapped (assuming you’re grounded).
So how do we get around this problem? By running a third wire that connects between earth ground and the chassis. In addition, we make the ground prong longer than the hot and neutral prongs. That way the chassis is connected to ground before the other two are connected.