Electric shock

Electric shock is established when our body behaves as a part of the circuit, offering a way for the current pass. This way is the one which less resistance.

It can have many causes, such as: contact with wires or sources energized, grounding absence, isolation fail, nature disturbances, accidental energizing, maneuver mistakes, electric arc (comes often with a lot of heat, causing burnings), etc.

PS: workers that have pessoal metals or electronics into them body must stay away from eletric-magnetic fields gerenerated by high voltage, whereas this field can increase the temperature of those metals or cause disfunctions in the electronics. And now, a doubt comes on: with all that discussion about wireless electricity, who will know the effects of these fields in our body?

Our body is composed of 80% of water, that is conductor (because of the minerals). Unless our skin (high resistance), our interior is propitious to receive an electric shock. It would be good to remember that our muscular and nervous system is naturally guided by electric impulses.


Depending on the state of our skin, if we were exposed to low voltages, we wouldn't suffer by an electric shock, but if our skin were sweated (less resistence), for example, we would.


Another danger is that the skin can be breached. Happening this (and as we already know that is has high resistance), the total resistance of our body would fall, what it would increase much more the current.


The damage of an electric shock depends on some factors:

• Current type: some people say that AC is more dangerous than DC, because it makes the victim stay holding the conductor (muscles contract without stopping).
• Frequency: just for AC. The more frequency, the more sensation threshold, the less dangerous.
• Current intensity: number of electric particles that pass through the area of the conductor per second. The more intensity, the more dangerous.
• Time exposed: maybe the most important factor. It's the amount of time that the victim stays on the shock condition.
• Way in the body: it's also important. The hand-to-hand way, for example, is very dangerous, because it would affect the heart and the lungs.
• Voltage: for the same conditions, the more voltage, the more current intensity, so the more dangerous.
• Resistance: as I said, depending on the resistance, the electric shock will be more dangerous (low resistances).

To avoid the occurrence of shocks, we always must:

• Use conserved and appropriate IPEs (individual protection equipaments). Remember that the company is obliged to supply and stimulate the use of these IPEs.
• Use tools inside of the techniques norms, and according to the voltage.
• Avoid the use of pessoal metals.
• Plan all the work to be made (beginning to the end).
• Know what and in what is moving.

Electric shock also have its benefits:

• By much time the electric-convulsing shock in the cure of schizophrenia (today they use drugs).
• Taser is a gun that fires two darts energized with high voltage (there're also closed contact versions).
• Beauty produts that promise to substitute exercises by stimulating muscles (with electric impulses).
• Defibrillator deliveries a therapeutic electric shock to the heart.

Always reminder:

Your family is your most valuable thing.

There's no work urgent enough that doesn't require a
SECURITY PLANNING.

How to turn off an energized system

This process is often confused. Its better concept is: a set of steps to eliminate any electric risks envolved in the turning off process.

Only switching the breaker doesn't guarantee a safe condition to work. Following these steps, you'll guarantee more safety for your services (here in Brazil there's a norm that says you have to follow these steps):

1. Switching the breaker.
2. Hinder the act of switching on the system, using a lock (its key only the worker has).
3. Verify presence of voltage (because nobody guaratees that the breaker relly broke the circuit).
4. Make the terminals have the same potencial (by jumping them), after the breaker. This step guarantees that there's no voltage between the terminals.
5. Grounding the chassis and the terminals.
6. Protection from energized equipaments in controlled area, to avoid accidentally touches. The worker must have to worry about his own work, and nothing else.
7. Finally, try to spread signs for warning the others that there're men working.

But nor always we have to follow the steps above, for example: we have a breaker inside a box (with a proper door). If its possible, we can equipotencialize all terminals and the ground, before lock the switcher.

In addition of this, there're some areas that require adaptations in the procedure (some special dangers). But the new procedure must be safer than the default.

The idea is to use the good-sense.

For turning on the circuit again, follow these steps:

1. Collect all the instruments and materials used during the service.
2. Instruct everybody to the process of turning on.
3. Remove grounding and jumps (include extra protections).
4. Remove warnings (note that this is almost the last step).
5. Remove locks and the authorization is given.

Following all of these steps (all of them is written in NR-10 (Brazil)), you'll guarantee safer conditions for you and your staff, reducing risks of electric shocks (and all its results).

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.).

Fluorescent lamps

A lot of things is spoken about the economy in our bills provided by fluorescent lamps. They dissipate, in comparation with tungsten ones (incandescents), 80% less; so, tendency is to think that they're friend of nature or more ambientally correct.

But, is it really true? Let's see some points.

• Incandescent lamp's fabrication process is much more simplified. Also, the quantity of materials is less. Fluorescents have electronic circuits that require a lot of energy for being constructed, beyond energy and materials for the fabrication of each component.
• Fluorescents have heavy metals (i.e. mercury) on their composition. Now-a-days, as the seletive collection isn't done (more spend of energy if it was) for this type of lamps (although there's already a process of descontamination of the pipe), they're still going to public garbage basket (sorry, I don't know the name of the place where all the city trash goes), contaminating rivers and people that there (unfortunablly) live and/or eat. Just for curiosity, the quantity of mercury in a fluorescent lamp can make not appropriate for human consumption 20k liters of water.
• Fluorescents have a very small power factor (compacts have 0,5). It means that a large room, that uses fluorescents for lighting, must have a capacitor system (more energy and materials for the fabrication), to correct the factor.
• In the other hand, incandescents heats a lot!!! In the truth, they just light because of the heat: the conductor inside the lamp becomes incandescent when it exceeds certain temperature (very high). The use of incandescent also overloads the refrigeration system, and makes the workers feel agitated.
• But its power factor is practically 1. In other words, to correct the power factor of a industry, you'd need less capacitors, because the incandescents would help the correction.
• Fluorescents have longer life than incandescents. But it's reduced as you use the switcher, in the same period of time. OSRAM says if you leave the room and will be back in about 15 minutes, it's better not to turn off the light.
• Fluorescents that use reactor (necessary for its functioning, that requires more energy and materials to be made) electromagnetic works with 60 Hz (here in Brazil), which causes visual discomfort. The newest ones work with about 35 KHz, that reduces this effect, but they generate harmonics, so you should install filters (more energy and materials to be made).
• The cost of the instalation, however, is cheaper, when you use fluorescents. Because fluorescents uses 4 times less current to generate the same light flow.

The problem is that today the news shows that just because fluorescent lamps consomes less than incandescent (for the same light flow, that is, better efficiency), they're a friend of nature. But how about other factors that I told above? It's a snow ball... They consume less, all right, but in terms of ecology, there's a much bigger impact.

It's obvious the overload that is saved from the electrical system of a country. Imagine what would happen if all fluorescents (20W) become incandescent (100W).

I'm not speaking against fluorescents (exactly because I only use fluorescents, as everyone I know does). I'm just showing the consequences.