Grounding
By Gabriel Torres on October 6, 2004


What is Ground?

Many readers have written asking about grounding and if it is really needed.

Electricity only appears when there is a potential difference between two points. For example, if we take two wires, one with a potential of 12 V, and another with a potential of 0 V, then we'll have a potential difference of 12 V. If both wires have 12 V, there will be no potential difference between them, and electric force will be zero..

Therefore, the mains electrical systems are made up of two wires, one called phase and another called neutral. The neutral wire shows a potential of zero and the phase wire is where the electric energy is transmitted. As there is a potential difference between phase and neutral, there is electric force. In mains distribution network the voltage is alternated, as the electric force of the phase wire varies along the time making a sine wave.

Ground is a signal having a zero volts potential. It is used to level the electric potential between electrical equipments. Usually the ground is connected to the metallic casing of the equipment. In equipments where the cabinet is made of plastic, ground is connected to the internal metallic case existing inside the equipment.

You must be wondering what is the difference between ground and the neutral wire, once both have a zero volts potential.

It happens that the neutral wire potential may vary due to the equipment connected to it and installed in your house or office. For example, it comes out of the public power utilities with a zero volts potential, but due to the connected equipment, the neutral wire may be showing a slightly higher potential, say of 6 volts. The potential difference between neutral and phase will then be 6 volts lower. As electrical equipment usually have a high tolerance this voltage drop will not affect its operation (in this example the voltage lowering will be from 127 volts to 121 volts, and the equipment operation is not affected).

But ground shows a permanent zero volts potential. Ground potential is obtained by means of a steel/copper bar into the ground. As Earth is an perennial source of electrons, its potential is absolutely stable. In case any equipment tries to alter the ground voltage (as it happens to the neutral), the voltage in excess will be diverted to the Earth, thus holding its electrical potential always in zero volts.

The issue is that the ground wire is meaningful only when we are operating with interconnected equipment where there can be no potential difference between them. An electric iron, a mixer or a lamp will operate without that zero volts ground reference, even if the neutral is presenting voltage differences, due to their tolerances. (That is not absolutely true if one considers the user who contacts a metallic part of the equipment while contacting ground simultaneously).

Problems Related With Lack of Grounding

Have you ever experienced an electrical shock when opening a refrigerator? This happens when the refrigerator cabinet electric potential is different from zero. As you are contacting the floor, that is at ground potential, there will be a potential difference between yourself and the refrigerator, building up an electric current as soon you contact the refrigerator metallic casing, causing the electrical shock.

This same kind of problem may happen with your computer cabinet or with any electrical equipment having a metallic casing.

The ground wire function is to provide a zero volt reference. Ground wire is directly connected to the metallic casing of the equipment whereas you will never feel such kind of shock in properly grounded equipment.

Now you figure that you are connecting the PC to a printer. That connection is done by means of a cable, right? What happens if the computer casing electrical potential is different from the printer casing? At worst, you will blow the parallel port of your computer or the printer's.

Another frequent situation is found in networked computers. If the computers are not properly grounded, you'll burn their network card whenever their casing show different electrical potential than yours. The network cable will play the role of interconnecting the computer casings provoking a shock between them, just as you experienced a shock when contacting the fridge door or the computer cabinet. This shock is an electric potential difference that will cause at least the inoperativeness of the network and, at most, the burning of the computer network cards having a potential difference between them. That is what happens in networks having several computers (naturally this problem only happens in cabled networks conducting electricity, while in optical fiber networks this problem will not show up, as fibers transmit light, not electricity).

There may be a potential difference between equipments that are going to be interconnected. The solution to level this potential difference is grounding.

But, as we've discussed earlier, in many cities in the world there is no ground wire distribution and it may be expensive to do it, because as we've discussed, one must bury a steel/copper bar into the ground - if you live in a house that is quite a simple task, but if you are in the 10th floor of a building, that could impose quite some handwork).

Then, what is the solution to level the potential difference between equipments? Unless you're working in an office where there are several networked computers, where a real ground is required, one can always use the "virtual ground" technique.

In your stand alone computer you will not have this potential difference issue between computer and peripherals, once you just level their potential difference. To do that, just interconnect their ground wires. Your voltage stabilizer can do that for you. Just don't cut off the ground pin of your equipment mains plug, and connect them to the same stabilizer in order to have their potential leveled, as the stabilizer interconnects all ground wires of its outlets. The only problem happens if there is a potential difference between yourself and the cabinet case, as you may experience an electrical shock whenever you contact any metallic part of the cabinet, or if you network several computers. Then ground will really be need.

If you want a true ground, however, we suggest you look for the assistance of a qualified technician specialized in buildings installations.

Some Remarks

The "virtual ground" technique we explained operates in order to level the electric potential between the equipments and to avoid them blowing out in the presence of a potential difference. In order to accomplish that one must interconnect the equipment ground wires by means of the voltage stabilizer. The mains plug ground pin must not be cut off as this technique will not work out. Naturally if you don't have a true ground connection, you'll have to let the ground pin of the stabilizer disconnected. That is, the stabilizer will take care of the equipment ground interconnection but its own ground pin will be disconnected.

Several readers asked us to discuss how a true ground can be installed without having to pay for a qualified technician. The most efficient workaround is to look for a metallic point that is connected to the underground of your building. In flats and commercial offices, you may get this point in the water pipe if it is a metallic one, or by means of the building concrete reinforcing bars (note: aluminum window frames will not do it). Therefore just buy a wire with the appropriate length to connect the ground pin of the stabilizer socket to the chosen beam or pipe and voilá, have a nice work!

In case you decide for the water pipe to act as your ground, don't forget to check if pipes are metallic ones, because if they are made of PVC you will not be able to use the piping. Note that, specially in the new constructions, taps are metallic but pipes are plastic. Therefore, take care!

Please do not attempt to connect the stabilizer mains plug ground pin to the mains neutral wire. Unfortunately many people do that. The problem is that if in the future someone wrongly inverts the phase and neutral wires in the distribution frame, your computer will blow up - literally speaking (we've seen this happen).

Another technical detail we forgot to mention in the first part of this series is that we were grounding our discussions on 110 volts mains public utilities. In one of the used configurations, one of the socket pins has a true 220V phase and the other one is the neutral. Else, the other possibility is that both pins are independent 127 volts phases whereas the potential difference between two phases is almost doubled, making up the 220 volts. In 220 volts distributions of this kind, the presence of a ground wire is even more important as the socket may not show a neutral wire (which, as we've seen earlier, has a zero volt potential)

Originally at http://www.hardwaresecrets.com/article/Grounding/18


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