a question about the mains outlet ground (earth)

mains outlet

i have a question about the ground (earth) of the mains outlet.

i have read somewhere that the neutral and the ground wires are usually connected together at the local power transformer. so there shouldnt be any voltage between the ground wire and the neutral wire. but ive seen in a number of places that there is a voltage of about 5-8 Volts between the neutral and the ground. ive also read that this is due to load imbalances and this is quite normal in a typical residential setting. but is this okay for a computer????

what is the solution to this? is it okay to make a separate ground by yourself? and for instance if i bury a wire in a flower pot close to my computer and connect it to the ground of the outlet which the computer is using, would it be dangerous?

grounding an outlet

The laws on building wiring in most countries require that the ground pin be connected to a dedicated connection to the earth at the junction box where the power lines come into a building. In many buildings this is a bare wire that runs around the periphery of the building. The neutral is connected to its own earth connection at the transformer which reduces the several kV of the distribution network to the 200 V wiring to your building (when you have a 110 V type circuit such as in the US. In countries where the outlet is 220 V they are floating). If there are currents in the earth that will produce a potential difference between the neutral and the ground at your socket. Adding a further earth connection for your equipment will not reduce this. Adding this additional earth connection for your equipment may be helpful for protection from lightning if done properly.

You should examine the laws concerning the wiring to make sure you are doing a legal connection.

3 pin 220 v us socket ground or neutral

The purpose of the 'earth' ground is to provide fault protection for you when you use your household appliances. By having one side of the incoming AC line connected to the 'earth', an internal appliance hot lead short to the case will cause a breaker to open or a fuse to blow - there would be sparks and a protective action.

If neither side of the line were grounded, the metal case of your toaster could develop a short to one side of the incoming line and you wouldn't know it. If your electric stove then happened to have a short to cabinet from the other side of the line, you would complete the circuit when you leaned against the stove to put toast in your toaster (you would get toasted instead of the bread).

The above reasoning is why metal military vehicles (ships, tanks, etc) take the opposite approach and use ungrounded systems. They don't want a fuse to blow or breaker to trip if one side of the AC line is shorted to the metal of the vehicle by battle damage. In this case the presence of a short is shown by 'ground detector' circuits that alert the operators.

In most developed countries, it is required that the ground pin of a three pin AC socket be connected to an independent ground wire that is returned to 'earth' outside the foundation of the building. This is done by burying a copper rod in the earth next to the foundation and connecting the socket grounds to that rod. Some jurisdictions permit using the metal water pipes of a building as a return path for the ground connection. There is possibility of galvanic damage to the water pipes from that sort of connection, so it is not generally the best way to go.

A few volts difference between neutral and 'ground' is normal. It is caused by the resistance and inductance of the wire that runs through the house to the AC point of entry, and by the resistance of the screw or clamp connections of the wires to socket terminals, breaker terminals, etc. There is no harm to your computer from the potential difference between neutral and the ground. Your computer case, like all the other appliances in your home, isn't connected to the neutral lead of the incoming AC line - it's connected to the ground pin on your three pin plug. The only time it has work to do is if a short develops in your computer power supply that connects the incoming hot line to the case - then a fuse or breaker should blow somewhere because of the current that will flow back through that ground connection.

As for adding a ground of your own - there is no harm in grounding the metal case of a computer or other appliance to a secondary ground connection. HOWEVER, if it seems necessary to do that when you already have a three pin grounded socket, there is something wrong with your socket ground. A qualified electrician should take a look at your circuit.

how are ground earthing done for house

Both previous post covered the issue..
If I were you I would be concerned about different potentials between E and N as if you assume that resistance of copper wire is very low (20m of 1.5mm2 has less than 0.25Ω) why would you have any difference?

If you would like to read more on this subject search this forum. THe topic was 2-pin v 3-pin or similar..

grounded socket

House_Cat said:

As for adding a ground of your own - there is no harm in grounding the metal case of a computer or other appliance to a secondary ground connection. HOWEVER, if it seems necessary to do that when you already have a three pin grounded socket, there is something wrong with your socket ground. A qualified electrician should take a look at your circuit.

Click to expand...

I checked the earthing system in my house and it seemed sufficient.

My problem arises with some electronic appliances (DVD player, AV Receiver, Subwoofer, and TV) which come from the factory with only two pins, not three pins. There's always some level of voltage present in the metalic case of those appliances.

I eliminate this voltage by making additional ground connection from the case to a grounding point. Up to this moment, this is sufficient ... only a little ugly connection

aaNg