This post is also available in: Portuguese (Brazil)
A grounding is the intentional connection of a electric to the Earth. It can be: protective, functional or temporary.
Protection: provides electric protection for human beings by offering a scape way to the current.
Functional: the Earth is used as a return conductor. For example, SWER transformers (single wire earth return) uses the Earth as a conductor (just one single-phase goes to the equipment. This SWER model is used in remote areas because its lower costs.
Temporary: as the name suggests, it is a temporary connection to protect the worker involved on the job.
To get a circuit grounded, you must have: a copper (or aluminum) rod, connectors, conductors and chemical treatment of the land (if needed).
To driven the rod into the ground, you can follow the following steps:
- Make a hole in the ground and put water into it; it will tend to be softer.
- After waiting a few minutes, start to stick the rod into the ground with your hands as harder you can. Then, put it out and add more water.
- Repeat this until you can’t get the rod deeper.
- Now use the sledgehammer and stop beating when remain approximately 4 inches of rod outside the land.
With the rod already into the land, make a hole around it, to put the inspection box (to avoid physical damages and accidents).
To connect the conductor to the rod, you can use a connector or a permanent solder. The solder provides the best connection, since it has less resistance (it requires a specialized company to get it done).
In the case you choose the connector, you must have a maintenance schedule, in order to prevent corrosion. Corrosion reduces the grounding efficiency.
There are different grounding systems, classified by (these are systems legally allowed in Brazil):
(the first letter is associated to the neutral with ground, and the second (and third) to the equipments with ground)
“I” means isolated; “T” means connected; “C” means conjugated; “S” means separated.
- IT (isolated neutral): the neutral conductor came from the transformer is not grounded. The equipment masses , otherwise, is grounded by a earth electrode. The leakage current in this case is very low and does not offer risk (high impedance between neutral wire and ground).
- IT (neutral with impedance): almost equal to isolated neutral. The difference is that the neutral wire is grounded by an impedance.
- TT: both neutral and equipment are grounded through different rods, and has different conductors (so you can use differential protections).
- TN-C: the same wire works as neutral and earth. The neutral wire is grounded at source(transformer) and it is distributed to every equipment. Here, we can not use differential protection, because leakage currents will circulate through the same wire as neutral, and it will not be detected by the protection.
- TN-S: we have different wires for neutral and earth. The neutral is grounded at source and the earth conductor is grounded through another rod and distributed to all equipment. Same as TT system, we can use differential protections.
- TN-C-S: mixed system with TN-C and TN-S.
When the resistance of your grounding systems is high, we can treat it by:
- Increasing the numbers of rod into the ground, but not indefinitely (from a certain number, the more you add, the less the resistance decreases).
- Using longer rods, reaching layers with less resistance. This technique is not effective to the first one.
- Using thicker rods, which requires more robust tools. This technique is not effective to the first one.
- Changing the chemical composition of the land. You can add special salts surrounding the electrode to reduce the land’s resistance. It is also necessary to replace the additive because over time it can increase resistance (dispersion of the salts).
There are other ways to reduce grounding resistance. For example, the use of bentonite. It has low resistivity and it is hygroscopic. It absorbs the water and makes the region surrounding the rod more humid.
In case you have not a grounding system, you can temporary use an isolator module. It works by separating the both circuits: primary and secondary of the transformer it has. So, if there is a fault into the PC and you touch it, the current will not have a path to follow and you will not receive a electrical shock.
The isolator modulo is equivalent to a conventional stabilizer, but it has double layer between the coils and the core (ensuring a better electrical isolation).
In my opinion, it is much more viable to make a grounding system (rods and earth conductor), since you can use it for multiple devices (computers, washing machines, electric shower).