earth connection and neutral connection in electricity?

Question

Regarding electrical circuits and connections

Answer 1

Electrical wiring in home construction for at least the last 30 years uses three conductor color-coded wiring. For the typical 120 volt circuit, the black wire is the "hot" conductor, the white wire is the "neutral" conductor, and the green or bare wire is the "earth" conductor. The neutral conductors and the earth conductors are all tied together at the circuit breaker panel, and are connected to the incoming neutral power line. They are also connected to "earth" at the panel by way of a ground rod, a connection to rebar in the concrete slab, or a connection to the incoming copper water pipe.

The reason for this is to reduce the chance of electrical shock. The earth connection is carried separately through the wiring to any exposed metal in appliances, electronics, power tools, or electrical device from which a shock is possible. This is the third, round conductor on many power plugs. A notable exception are "double insulated" devices for which the earth conductor is usually missing.

You may say, "Yes, that's good, but why not just use the neutral connection for that purpose?" There are several good reasons. When you realize that electrical shock can be life-threatening, you don't want to compromise your safety. That's one reason to have a dedicated earth conductor. Also, I have encountered instances where receptacles are miswired, putting the hot conductor where the neutral should be. (Looking at a receptacle with the round [earth] pin at the bottom, the left [wider] conductor is neutral and the right [narrower] conductor is hot.)

The other reason is for circuits that are protected with a Ground Fault Circuit Interrupter (GFCI). The GFCI is essentially a sophisticated circuit breaker that senses an imbalance in the current flowing through the hot conductor and the neutral conductor. If these two currents are not exactly equal (but in opposite directions), there must be another path through which some portion of the current is flowing--which means there is the possibility for electrical shock. This "leakage" path may be through the earth conductor or through the user. The GFCI breaker will trip in either case. You can see in this situation how it is necessary to keep the earth conductor separate from the neutral conductor.

Answer 2

The neutral is the return path for the hot (load) in the circuit and is grounded at the panel.
Equipment cases are now often grounded to earth also, because if a hot wire should come loose and come in contact with a conductive case (like stove or fridge or whatever) . . . then a person would get shocked when touching the appliance unless the case was connected to ground also, hence, the green ground wire in all new construction.