Ground system

Ground is an intentional linking of a circuit (or chassis) to the ground. It can be for: protection, service or temporary.

Protection: secutiry for human beings by offering a path to current.
Service: ground is used as a conductor. For example: MRT's transformers use the earth as conductor (current goes through one conductor, e returns through the earth). This type of transformers is usually used on contryside, because it costs less.
Temporary: it's a temporary ground that protects the workers when they're doing a service (maintenance).


A ground system requires: copper rod (or aluminum), conectors, conductors and chemical treatment of the ground (when it's necessary).


To inject the rod in the ground, follow these steps:

• Dig a hole and put some water on it, to make easier to inject the rod.
• After wait some minutes, try to inject the rod until you can. Take it off and put more water.
• Repeat the steps above until you can't inject more with your hands. Now, take a strong hammer and start to beat the rod.
• If you can, take off the rod and put more water. Beat it until it remains 10 centimeters.

Dig a hole around the point where the rod was injected for inspection box. It gives protection for the conector "rod-conductor" against physical damages and accidents.

To connect the rod to the conductor you can use: conector or weld (permanent). Using weld is the best, because the result of the explosion is pratically inexistence of resistence between the rod and the conductor.

The use of conectors require periodically maintenance, because a corrosion (oxidation) appears, naturally, after some time. It raises the contact resistance (rod and conductor), making the ground system inefficient.

There are different ways to build a ground system.

• IT (isolated neutral): the conductor neutral that comes from the transformer isn't grounded. The chassis of the machines is conventionally grounded, through ground conductor (rod in the earth). The escape current is very small, and don't offer danger for us (impedance between ground and neutral is big, for example, 5kOhms). A second escape current must be considered improbable, just because it's necessary a monitor to accuse the first problem (to be solved).
• IT (neutral with impedance): there's a impedance Zs (for example, 1,5kOhms) installed between neutral and ground. It's the same thing for escape currents, that just one is small.
• TT: both neutral and chassis are grounded, with different rods. You can use RCD (residual current devide), because neutral and ground conductor aren't the same.
• TN-C: neutral and ground are the same conductor. The neutral is grounded in the transformer, goes to the equipaments, that have their chassis connected to the neutral. (This is the kind of ground system that is established when we make a jump from ground to neutral). Here, you can't use RCD: it wouldn't even detect.
• TN-C-S: in one part of the circuit, neutral and ground are together (can't use RCD); in another part, there are separated (you can use RCD).

When there's already a ground system installed but it's offering high resistance, we can take some actions:

• Add more rods. You must have to consider the distance between them, to avoid
  
  mutual resistance (when one rod is inside of other's field). (To avoid it, the minimum distance is twice of the rod's height (this is my opinion, because I have seen people saying that the minimum distance is equal to hog's height)). From a unspecified number (it depends on each case), the resistance decreases just a little bit for each rod added.
• Go deeper with the rod (amending one rod to another). Be careful, because some terrains have deeper layers with high resistances.
• Change the rod to one thicker. This technique require robust tools and the decrease (resistance) isn't so much.
• Treat chemically the earth. You can add special salt around the rod, but spaced; otherwise, the corrosion of the rod will be accelerated. It's necessary that you change the additive periodically: the salt get dispersed along the time. In small ground system, this technique is very efficient and viable.

There are more ways to reduce ground resistance. For example, adding bentonite to the earth. Bentonite is a type of clay that is higroscopic and has small electrical resistivity. It abosorvs water (higroscopic) and the region around the rod gets wet (the water helps to decrease resistance).

If you don't have ground system, you can use temporary a module isolator. It separates the primary circuit from the secondary. So, in the case that it has a isolation problem in the computer, there would be no way for current to flow, and you wouldn't take an electric shock. Using a module isolator for a equipament (for example, computer), you can't ground its chassis, or even mount a net with grounded computers (there comes a doubt: "someone uses ADSL, that has a phone line (previously grounded, right?) connected to the modem, that is connected to the computer. Will the module continue doing what it promises?").

A lot of people say that the module dissipates escape currents, by transforming it into heat. In the truth, sometimes the escape current (that returns to secondary coils) gets high enough to warm the conductor (and the coils), and thus, causing the wrong perception that the module is transforming the escape currents into heat.

The difference in the module is that its transformer is twice-isolated, guaranteeing no contact between the coils and the magnetic iron, and also between primary and secondary neutral.

In my opinion, it's much more viable you build a ground system (rog and conductor), since you can use it for all equipaments (computer, refrigerator, electric shower, etc.).