why not simply short-circuit the "neutral" and ground and use only two terminals in domestic power supply?

Question

what's the meaning and function of the "live", "neutral" and "ground" terminals of a regular household outlets?

Answer 1

The purpose of a separate grounding wire in a circuit is safety.

This wire does not carry current during normal operation. Instead, it connects to ground components such as metal outlet boxes in which receptacles and switches are installed, metal appliance cabinets, and frames of motors.

Although the ground wire does not normally carry a current, it will carry current in case an electrical short develops. In this case, the grounding wire directs the current safely to ground rather than shocking the person touching the appliance.

The neutral wire, although grounded, is not used for safety. It carries current and is needed to close the electrical circuit. This allows the current in a branch circuit to flow from the electrical service panel through the appliance and back to the grounding bar in the service panel.

If both neutral and ground wire is carried by a single wire. If there is a short-circuit and the neutral portion of the wire becomes open circuit, the whole device could become "LIVE" and be extremely dangerous. However, if the ground is kept solely for safety purposes, this event is not going to happen, since the ground does not carry current, unless there is a leakage.

Answer 2

A lot of electrical instruments use no ground, as is evident by just 2 plugs.

The 2 are connected earlier in the system. Typically that are connected in the distribution box (circuit breaker panel).

The live wire carries the + side of the voltage. The neutral carries the - side, and it is connected to the ground as described above. Typically there is almost no current on the neutral (except for some current which is induced from wires carrying the + and - current) (think of it as current or power leaking from the wire).

The ground is connected to the metal housing and other components. it is for safety, which is why it is often called safety ground. If a component shorts + to the metal housing and there is no ground, the housing would be at a + voltage... if you came into it while making contact with a ground or neutral, you could be severely shocked or even killed. Ground provides a path for this current, causeing a very brief near short and tripping the circuit breaker.

When you connect ground and neutral, there are several possible problems.

First, you get a lot of noise on your neutral. Since the electrical appliance is looking at Hot and Neutral, any noise it sees is constantly changing the voltage it sees. This noise can come from induced curent as described above, or it may come from other appliances that do not have a proper ground connection - these devices will be looking to return the - current to the cource thru the path ofleast resistance - if they see this nice neutral wire connected to ground, they will pass some of their current back on this wire.

This also produces a small fire potential. As a normal course, these other devices will be passing their current thru your ground connection to neutral back to the cource. You have no idea what this current will be passing thru - the material may be flammable or likely to heat up producing a fire.

Since this is a power supply, you typically want either the + or - side of the output connected to ground for the same safety reasons as neutral and ground above. If this is connected to ground, and round is connected to neutral, the grounded leg of the output sees all the noise on the neutral leg. This may be noise as described above. this will also be noise produced by the varying current interacting with the resistance of the wire. This noise can wreak havoc with electronics, perhaps dmamaging them.

Answer 3

The neutral side is supposed to be 'ground' at the junction box. But if the high ('live') side of the line ever contacts a metal part of an appliance, a shock hazard exists unless that metal part is grounded. That's the purpose of the 'ground' wire in the plug. It's supposed to be connected to the 'frame' of the appliance.


Doug