I know how power is generated and transmitted. When it is High Voltage 3-Phase Supply, it makes sense to ground the neutral of the Star Connected Secondary of the transformer to Ground (or if it is a Delta to create an artificial neutral).
But when it comes to regular 110 V household (US) supply, the neutral is essentially a ground, SO why create an additional ground ? WHy not just connect the neutral to the ground and be done with it ?
I can understand that when it is 220 V supply there are two phase supplies and there you need an additional ground. (This is assuming the supply voltage between 2 of any 3 phase supplies is ~220V and the Voltage between any phase and ground is 110V).
When the nuetral carries current it is no longer at ground potential due to resistance in the wires. Think of the wires as resistors instead of ideal conductors and it should be fairly obvious why (hint: V=IR). A “ground” is just a nuetral that never carries current, and as such should always be at ground potential. Ground and nuetral are usually connected to each other (and to earth ground) near your fuse box.
Not true. Use any voltmeter to measure the P.D. between neutral and ground. Besides, for a balanced 3-phase load, the neutral will carry no current (the 3-phase currents cancel out each other).
If the neutral carried any voltage, by now people will be using this free voltage between ground and neutral to power things
That wire is called Protective Earth and the purpose is to protect users against the posibility that the metal parts of the device may be accidentally connected to the live wire. Howthingswork probably explains it in detail.
Oh, and, Andy, you are mistaken and engineer is right. I am an electrical engineer myself if that helps.
The nuetral is connected to the ground at the service. I shall explain why.
The ground rod (or grounding electrode) has a ground wire connecting it to the service ground bar. The water supply in the house must also be grounded with a wire. Then all three (ground rod, water, and nuetral) are all bonded to the actual panel itself. So now every thing in the house is at the same ground potential. This way you wont have any stray ground currents looking around for the path back to the power companys ground(if we relied on nuetral only). By bonding everything in the house, we don`t care what sort of ground the power company supplies because every house takes care of itself.
This also helps maintain an efficient grounding grid for the power company.
Andy - You third paragraph is a little confusing, are you refering to a three phase service(industrial/commercial) or to 110/220v. single phase service(residential). Residential services are 110/220v. single phase. Confusing, but there are two hot legs and one nuetral. Between the two hot legs you get 220v. and from each of the two hots to ground you get 110v.
The need for a separate ground and neutral lies in the need for all parts of the power supply to be at the same ground potential. Electricity seeks the easiest path to ground, and it will energize all paths to ground. If there were different ground potentials in the same circuit, the easiest path may not be the one in the wire in which it is intended to travel. It may be through you.
In North America, the power company supplies a single phase primary to the transformer near your house. The neutral is supplied thru a grounded conductor to that point. The wires are split from the transformer into a primary conductor (110v), a center tap to the transformer (110V) 180 degrees out of phase with the primary, and a neutral. This is why you have 220V available in your house.
These three wires go to the meter and main panel. That location may or may not be (but probably is) at a different ground potential than the transformer. The main panel is then grounded (usually with one or more grounding rods buried in the ground near the house), to rectify this. The water supply pipe, which is buried, is also probably at a different ground potential, so it is bonded to the grounded main panel.
Now “everything” should be at the same ground potential.
When you run a circuit in your house, you run the 3 wires (hot, neutral and ground) back to the panel. They do not share a connection anywhere in this part of the circuit. In the main panel, you then connect the hot to one of the conductors in the panel, one to the neutral, and one to the ground.
“But”, you say, “the ground and the neutral are connected to each other in the panel”. This is true. It is intentional. This is to ensure that the circuit and your panel (and all the circuits in the house) are at the same ground potential. If there is a short, there is no easiest path to ground. All paths are the same.
Also, the nuetral will only carry unbalanced current in a three phase environment. If there is a load on your service and you clamp an amp-probe around the nuetral at the service you will get no reading, but if you try to lift that same nuetral out of the lug, you will get all manner of sparks. There needs to be a ground potential for the circuit to work and the nuetral is a “controlled” ground.
Did I explain this right you electrical engineers?
Farms are notorious for having “stray” grounds because of the vast distances between electical components at different ground potentials. They have "leaky’’ grounds and the cows don`t like that. They can actually feel the ground currents and it disturbs their milk production.
The reason that code is differant for farm outbuildings is partly that they may well be a long way from the supply, hence long cable runs and thus high earth loop impedance paths.
Quadruped animals are especially vulnerable to ground fault currents.
If a fault occurs and the current is grounded locally, there will be concentric rings(in effect) of differant potentials around the earthing point, having a significant differance between fore and back legs means it is likely that any quad animal in the nearby vicinity will experience an electric shock,and 60Volt is enough to stop the heart of livestock, especially cows.
Earthing points, such as spikes, buried plates etc on farms need to be either indoors or fenced off so that animals cannot get near.
When lightening strikes ground, any livestock in the area will have a very high risk of death, for anything up to 100 metres, and when you think of possible strike sites such as service poles, it’s no wnoder that this is one of the more common ways for livestock to suffer accidental death.
Humans and small animals are pretty much ok, it’s possible to get a shock through both legs and although this might be somewhat alarming(and very funny if it happens to one of your mates)) for a man to undergo, the main risk of heart stoppage is very unlikely.
Um, sorry, but ECG is correct. When there is no current in the neutral conductor, the neutral is at earth ground potential. When there is current in the neutral conductor, the neutral is not at earth ground potential…
