ground loop - a term with interpretations:
- Metal structure, buried deep in the ground and it has a relatively low electrical resistance, serving as earth electrode.
- Neutral conductor in the complex from the equipment of a building that are essential for the protection of metal structures in working order is not a source of electrical hazards from bringing them potential.
What has been said will make the ground loop independently predosterezhot from impermissible actions.
From the history
As the story goes, the inventor of the grounded power outlet (United States standard) introduced an extra touch when his landlady was hit inadvertently shock. Wanting a little cool, she decided that the fan will do. At this time, through the window into the cat climbed up and jumped. The hostess and the device proved to be in the way of animal... As a result of the accident was not injured cat. But electric shock forced the woman to tell Philip Labre (Philip Labre). Engineer analyze what happened and realized that the circuit would not become isolated on the person, he grounded the fan housing.
With regard to other countries of the world, awareness of the need for a protective earthing contact it for a long time. Described in more detail in the section on sockets. Today protective earthing introduced in the country electricity circuit in the world. rosette shape is different, but the fact of the need for action is well aware of.
According to Soviet literature during the reign of Nikita Khrushchev energy output was 230 Bln. kWh. Which exceeded 120 times the figure in 1913. Since the Soviet political scientists have promoted the communist system. According to reports in the world consumption has doubled every ten years. And the Soviet Union turned out, of course, ahead of the rest. In this case, the safety overshadow rare people know what a ground loop.
Occurred in the early 70's economic crisis has shown that the steady-material wealth in developed countries is capable at any moment falter. When prices rose to 12 dollars per barrel, manufacturers have sounded the alarm. We began to think about the energy efficiency class of household appliances. The first innovative energy-saving technologies tested California. And the government to monitor the results (meet the expectations of the instigators of the event).
Schematic sketch of the ground
As a consequence, there was a tremendous increase in the number of electrical appliances at the same consumption as a whole. Now we began to think about ground loop, differential automatic machines, design and demand.
The need for grounding
In everyday life, without the possibility to ground the enclosure must annihilate the. This general rule, Godea in most cases. Even for three-phase circuits. Vanishes not need housings and other parts of plants, providing a current supply circuit which are not protected by the differential machine. This simple rule follows from the obvious reasons: in the two-phase current circuits do not care where close to the ground. If the accident is not immediately detected (by differential machine), circuit occurs through any part of the circuit:
- Sewer pipes, water and gas.
- Reinforcement of buildings.
- Electrical panels.
Predict where the current moves, difficult. In household appliances zanulonny the subject should be protected by differential automata. Just do not say, but the requirements of the SAE and GOST R 50571.11 unequivocally comply with the instructions. According to the norms, rely vanish all (there are exceptions) metal objects in the kitchen and in the bathroom and put on consumers differential circuit breakers. Which ensures safety in the cases discussed above.
With regard to the three-phase circuits (with gluhozazemlonnoy neutral), in which the body vanishing considered reliable protection. In one of the supply potential capable branches be below ground, the leakage current will go there. If the cabinet is simply to start at the ground loop is formed a resistive divider where it is difficult to predict the potential of a particular point. The lion's share of the current goes through the failure that has taken the current carrying structure a bare hand. Zanulonny body is already possible, but sometimes you need to be grounded.
Protection against single-phase fault in a network with isolated neutral
With protective grounding circuits with isolated neutral book begins MR Nayfeld from known libraries fitter. From the description, it follows that calling with any current-carrying capacity of soil structures becomes mandatory protection measure. The operating personnel in complete safety. How to determine that there was a leak? Powerful equipment continues to operate in the conditions described.
single-phase circuit tutorial mode is seen only as a potential danger. The equipment continues to operate, and insulation monitoring equipment will signal the repair group, introducing in the course of future events. There is a serious problem:
- The loss of electricity in the wires heat and soil. Besides the obvious trouble it threatens damage of the polymer insulation of cables and wires.
- It creates a potentially dangerous situation. Perhaps the formation of the points where the manifested step voltage.
- Phase unbalance inevitably manifests itself in such a situation becomes potentially unfavorable operating conditions for energy suppliers and consumers. There may be a voltage rise or fall on other lines.
LEP brigade knows how to behave in a dangerous situation, what to do ordinary citizens and even businesses? To deal with the situation on the spot, the relay types are used:
- Relay skew phase voltages operates on the described principle. When ground fault load one branch grows strongly. Disturbed stress balance of the term phases. The controller tracks the time and disconnects the load or will alarm.
- Zero sequence relays operate on the basis of the method of symmetrical components. Special rules current is decomposed into a sum of vectors. The appearance of certain components in the equations indicates the occurrence of an undesirable situation. The zero sequence voltage signals the emergence of a short circuit.
It is considered unsafe for phase distortion of the equipment. Want to disable refrigerators (compressor) and air conditioning in the event of such situations. Protective earth as simple way to help solve the complexity of identifying the situation. Particularly, if the circuit to control a current transformer.
Electric floor heating
It follows from the above that the areas previously provided exclusively by oil, today partially transferred to the electricity supply. We are primarily talking about heating. There is reason to think about home insulation and safety. For example, a warm floor system covers the whole area of the room. The danger is able to come from all sides:
- The moisture from the basement rises due to capillary action up.
- Flood will turn into a catastrophe. It is dangerous to walk on the wet floor.
Concrete, brick conduct electric current. How to make ground Floor heating systems? Do not rely on statistics, they say, the low probability of hitting a person, but... Let's say a man entered the room, where wet cleaning is carried out, barefoot - not trodden. He took a hand mixer for and received a full shock. The mechanism of the incident:
- From overheating or due to old age, the electrical insulation of the cable is cracked.
- Concrete screed has become more like the craquelure due to the elapsed time.
- Water poured on the floor, penetrated to the cable. Ground objects was not close, the system continued to work as normal: no current path.
- When one bare foot stood in a puddle, and then took the hand of the mixer body he closed circuit. Part of the current went through the man, other - on the circuit to heat the room.
In this situation, it is considered that the resistance of the resistor cable is very high, a person goes through a significant current. Skeptics say - at the entrance stands a differential circuit breaker, which immediately zasechot leak. But as a rule, it is better to avoid a dangerous situation than wonder why the floor is cold. Machine being delivered according to the directions A. Zemskova probably works apart from the lighting and sockets. The owner does not know that sex is no longer heated.
It's obvious reasons, the ground loop is proposed initially to arrange differently. If you can not find a shielded cable resistance to annihilate the braid, it is permissible to choose the metal hose. Electric wire lay floor heating zigzag. This does not contradict the general requirements of regulations and clearly reduce the danger. Allowed to ground the reinforcing mesh sandwiched on top of the cable, in addition, the general rules recommend concrete reinforcement to connect with the ground. Naturally grounded structure may be used in security systems.
Where to arrange the earthing
Ground loop is connected to the ground via the earth electrode. An important role is played by the resistance between it and ground. According to industry standards, the overall impedance of the protection point is not allowed more than 5 ohms. For household appliances loyal standards - enough 10 ohms. The exact values in the table. The design of the earthing switch is assembled from metal strips, tubes, angles.
Permissible to arrange the earthing of the European standard, but the authors believe that most readers flipping lazy English-language literature. Meanwhile, the publication of MR Nayfeld provides the data for the calculations. According to the dependence of the resistance from the ground steel resistivity of the soil may select earthing geometrical dimensions (length, cross section). It should be noted that the given value represents the current run-off process with earthing. The internal resistance of the circuit is of conventional physical formulas. The longer the conductor, so it is significant.
Soil resistance is taken from the table depending on the type of soil. In addition, the author presents data on individual grounders. This allows to combine the steel strips with different designs, achieving the desired effect. European standard recommends to collect "comb". The strip steel is at a depth of 0.6 meters or more, from it down (up to 5 meters) are uniformly spaced metal rods.
The graph shows that the earthing dimensions determined mainly ground and which is advantageous to reach the groundwater, reducing the amount of work. It is clear that the metal will begin to rot quickly. To get rid of the trouble may use primer (anti-rust) on metal or choose different location earthing burial.