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the appearance in the household of electricity was raised and the issue of its safe use. Let's see how to solve this important task, we will understand: what is zeroing, how earthing works, how to do zeroing in a private house with their own hands. And besides, can you use zeroing instead of grounding.
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What, how and where does it take
It is known that electricity is produced by power plants. From them, an electric current tens of and hundreds of thousands of volts goes through three wire-phases to the consumer.
The voltage is so great because according to the laws of physics, the higher the voltage, the less the loss in transmission over long distances.
Then the step-down transformer substations transform high voltage into a much lower (but still dangerous), and by wires or underground cables it will come to our house.
The current must come to the electrical appliance, do a useful job and leave. In the case of alternating voltage, used in everyday life, phase (feed) and neutral wire serve for this purpose. Where the electric current comes from, it is understandable; but where does the electricity go? In the ground! A bit simplistic, but by and large it is. It's in the ground.
The substation transformer has a ground connection to a separate line wire. This is the very "zero" in ours. Particularly curious can see this by examining a conventional transformer substation with air lines. 3 wires came in, out 4. At the input there are three phases of high voltage, at the output there are three phases of low voltage and zero wire.
And now let's move on to the main thing - human defense.
Grounding in an apartment
The most reliable way to protect against electric shock in everyday life - electrical appliances. After all, many of our domestic helpers have metal (read - current-conducting) housings, and as a result of breakage or damage to insulation, the phase wire can contact the body of the device. And then touching it becomes deadly dangerous ...
To avoid trouble, the body of the device is connected to the ground. Now, when the phase hits the housing, a short circuit occurs and a protection trips the current supply.
In modern apartments is carried out on a three-wire scheme:
Phase;
zero;
Earth.
The electrical equipment is grounded through the third contact of the plug and. The situation in houses where it is mounted on a two-wire circuit is more complicated, and there is no ground wire in the sockets. In this case, the grounding wire should be carried directly from the body of the device.
Where to get the "land" in the apartment of a multi-storey building? The answer is simple: in the electrical panel installed on each floor.
Before you do it (better, of course, do it with the participation or under the supervision of a professional electrician), carefully study the electrical panel. After all, if there is no reliable grounding at the shield, connecting it to the grounding wire of the apartment is not only in vain, but also dangerous!
Let us explain with an example. The neighbor has a short circuit. The current will go the following way: neighbor phase - "zero" neighbor - floor electric panel - your ground wire - the housing of your device!
Safety shutdown device
To improve the safety of operation of electrical. devices use the so-called protective circuit breaker, in short - RCD. Together with the RCD, 100% guarantee protection of a person from electric shock.
Let's analyze the principle of the RCD, for which we will present as a water supply system. Water flows through the pipes, as well as current - through the wires. And if suddenly a hole formed in the pipe, the water begins to leave, and its quantity at the outlet of the site will be less than at the entrance. RCD and controls such a leak, but not water, and electricity.
If the housing of the device is energized, but there is no leakage - the RCD does not react. But as soon as the shell touches the person - there is a way for the leakage of current, "hole" - the RCD for a split second opens the circuit.
Zeroing
According to the Rules of el. security, zanuneniem called: ".... connection of the equipment body with a neutral protective conductor ". Now let's talk. We have an electrical appliance (say, a washing machine), which must be grounded. The plug of the machine and the socket are three-pin, but the wiring is two-wire, which means that we do not have a ground. But we know that the "zero" on the substation is grounded, so why not connect the "zero" and "ground" pins in the socket? In no case!
Let's read the wording once again: "... a zero protective conductor." That's the thing! After all, "zero" in the socket conductor working, not protective, and put a jumper between ground and zero in the outlet can not:
a) this may result in a short circuit;
b) if zero has poor contact, the phase through the device will go to zero of the socket, and through the jumper and ground wire - to the body of the device.
We read the rules further: "Zeroing is intended to eliminate the danger of electric shock when the body is closed ... in three-phase four-wire networks ...." But in the apartment, the network is single-phase! Here in a multi-storey house the network is three-phase four-wire, so you can perform zeroing no closer than in the house's distribution cabinet.
Consider a couple of situations
1.
When you have connected the housing with zero wire (working zero). After some time, during the repair of the shield, accidentally changed the phase and zero. Result: on the body of the machine you have a phase! You will not get a dangerous but unpleasant blow, even if you have an RCD, or you can seriously suffer.
2. The same connection. The winding of the motor was overheated, and a breakdown occurred on the body. The housing is energized, but the RCD does not work: there is no leakage! The winding is heated until the wires are fused, and the automatic protection device does not work from the increased current. And the engine "kirdyk, and before the fire near!
You can think of other situations, but they are all resolved if the wiring is done in a three-wire scheme with reliable grounding. That is, the machine is connected without zeroing in the socket, and is reliably grounded (Fig. 1).
At any phase closure, the circuit breaker or an automatic circuit breaker is triggered by turning off the power.
If the wiring is two-wire, you must conduct a ground wire from potentially dangerous devices with metal housings to the electrical board, making sure that it is grounded.
In the conclusion about nullification
Remember the truism - any work with electrical networks is performed only when the voltage is off! If the work is carried out under voltage, use reliable and tested funds protection: dielectric gloves, etc. You have one life, and you should not risk it with trifles: electricity does not forgive frivolity!
As usual, we are waiting for your,! Good luck in job!
Hello, friends!
In this article, let's talk about what zeroing is, where it is applied, and about the main errors in its design. The topic is not simple, the forums are constantly debating.
It is interesting that often even electricians can not correctly say what is different from grounding. Let's understand. First of all, let's see what is said about the abolition in the PUE.
Zanuleniem in electrical installations with voltages up to 1 kV is the deliberate connection of parts of an electrical installation that are not normally under voltage, with a solidly grounded neutral of the generator or a transformer in three-phase current networks, with a grounded terminal of a single-phase current source, with a grounded middle point of the source in direct current networks
Simply put, zeroing is the connection of the body of an electrical appliance to a zero wire.
Now let's see what the PUE tells us about grounding
Grounding of any part of an electrical installation or other installation is the deliberate electrical connection of this part to the grounding device.
In simple words, grounding is the connection between the body of an electrical appliance and the earth electrode. A grounding device is a construction made of metal pins, driven into the ground.
Now let's see how the most common power supply systems for apartment buildings are arranged.
The old Soviet system TN-C
A more modern TN-C-S system
In both schemes, a combined zero conductor PEN is used, which is grounded at the transformer substation.
The main difference between them is that in TN-C-S there is a separation of the combined conductor into an operating zero and a protective conductor. This is done in the introductory common house shield (ASP). Re-grounding is mandatory.
If you look carefully at the diagrams, it becomes clear that the working zero is always connected to ground, that is, grounded. And the question arises: what, in fact, is the difference between grounding and zeroing? After connecting the body of the device with a working zero, we actually connect it to the ground.
In fact, there is a difference. It consists in the principle of action.
Earthing is designed to draw current to the ground. This reduces the dangerous voltage on the body of the device or device.
Zeroing is designed to create a short-circuit effect when the phase breaks into the housing. At the same time, the machine will fire and turn off the emergency line.
Thus, zeroing and grounding in TN systems works simultaneously, so to speak, in one bottle. Therefore, the third protective contact in the European sockets in TN systems is both grounding and zeroing.
Proceeding from this, it is correct to speak about a combined conductor PEN, working zero conductor N and protective conductor PE. At the same time, even electricians do not always understand the difference between PE and N, and it is very significant.
Usually, when some "electrician Uncle Vasya" speaks of zanuleniya, then it means different kind of collective farm type jumpers in sockets and the like connecting the protective conductor to zero. And it's dangerous.
Wrong nullification can instead of protection can cause a tragedy .. And there is such a pseudo-protection very, very often.
Let's see how correctly done protective zeroing and what can not be done categorically.
Remember, the separation of the combined conductor into an operating zero and protective zero must be done in a general input device (ASU). And from there the protective conductor should go to the floorboards, and from them to each apartment.
Thus, we get a five-wire riser: 3 phases, working zero and protective zero. In this case, we are not talking about the so-called zanuleniya, since each apartment receives a separate protective wire (TN-C-S and TN-S systems). It must be connected to the third contact of the sockets.
In old houses with unmodified wiring, there is usually a four-wire riser: 3 phases and a combined zero PEN (TN-C system). This is where the complete mess begins and terrible shoals.
Everything starts in the floorboard. Often it makes an independent division of PEN into PE and N.
This option has the right to life, but only when respecting important rules. Here are the main ones:
Rule 1. In single-phase circuits it is forbidden to separate the neutral wire (PUE - 1.7.132).
How to determine which network is in your home? In relatively inexperienced houses, the access platforms are four-wire: three phases and one combined zero (PEN). That is, three-phase risers are used, respectively a three-phase circuit.
In very old houses, stalinkas and Khrushchevs, a two-wire riser is often used, in which only the phase and the working zero. A distinctive feature of such houses is the lack of access panels. Stoats go in the mines between the apartments, and in the apartments are specific "humpback" shields. In these houses, as a rule, a single-phase network is used.
Rule 2. The combined PEN conductor must be a section of at least 16 mm in aluminum or 10 mm in copper.
That is, the zero riser must be a section not less than the indicated one. In many houses the cross section is smaller, in this case it is impossible to divide the combined zero into a protective and working one. If you have a Soviet-built house with gas stoves, then in 80% of cases the riser in it is frail.
Rule 3. After separating PEN into PE and N, they can not be reconnected.
Here, I think, no explanation is needed.
Rule 4. Protective conductor PE must be non-disconnected.
That is, it should not be put on the machine and other disconnect devices.
Rule 5. To divide PEN it is necessary BEFORE all automatic machines, knife switches, switches.
It is better to do so: take a brass tire and screw it with screws to the shield so that there is contact between them. From the zero riser through a separate nut make a tap on this tire. Connect PE protective conductors from the apartments to the bus.
If at least one of these rules is not met, then it will not be a defense, but a dangerous collective farm.
A little more about what can not be done
1) Connect the protective and neutral contacts in the socket to the jumper. This is one of the most dangerous mistakes!
If there is a fire, damage or accidental detachment of zero, a dangerous phase voltage will immediately appear on the housing of all devices connected to such outlets. In this case, neither the RCD nor the automaton will work. Hello, death.
The same effect will occur with an occasional phase change and zero.
2) Place the zero and protective conductors on one screw in the shield
PE and N must always be on different terminals (tires). Moreover, each wire from a separate apartment must be clamped with a separate screw.
3) Zanlyat on an ungrounded (unconfined) shield.
Usually all boards have direct contact with a zero or protective riser (nullified). But sometimes there is no contact, for various reasons. For example, the connecting wire fell off. Zeroing on such a shield can lead to the appearance of dangerous voltage on its body.
In practice, this kind of jambs are found very often, in different versions and combinations. I can advise not to be too lazy, to study PUE, and also not to trust your posting to dubious personalities.
In all residential buildings To protect against the effect of electric current, earthing or zeroing is used. In some cases, the electrical shield is grounded and, at the same time, the zero core of the main cable is connected to the same shield. However, the question often arises as to whether it is possible to use zeroing instead of grounding, and vice versa.
Grounding and zeroing schemes
These protection schemes must be used very carefully. First of all, this is due to the uneven distribution of the loads on the phases. With the same load for each, a small current flows through the common neutral wire. However, if only one phase of three is loaded, the current value in the zero wire will be the same as in this phase.
In residential homes, zeroing is not recommended. As a rule, zero veins have a smaller cross section than the phase lines. Zero wire very often remains uncontrolled, its connection weakens, oxidation occurs. With strong heating, it simply burns out. In this situation, there is a direct hit of the phase on the shield. Through grounding, the current enters the apartment and disables all grounded equipment. Household appliances are under tension, as a result, the probability of electric shock is increased.
Thus, it is undesirable to use zeroing in residential buildings. Usually, it is used in industrial plants, where the phase load distribution is more even, and the neutral wire performs the function of protection.
What is nullification?
If you know about grounding, almost everything, then about zeroing, many have a very vague idea. However, it is used quite often and for proper operation, you need to know its device and the principle of operation.
In electrical engineering, the connection of the neutral wire of the electrical network to the housing of the device, equipment and other consumers is referred to as zeroing. Unlike grounding, protecting people, zeroing, first of all, protects the equipment. Therefore, talking about zeroing instead of grounding is not entirely correct. Each scheme is designed for use in a particular area. When protecting the equipment, artificial nullification creates a short-circuit situation in which the circuit breaker is triggered.
For stable and reliable work of zeroing, it can be grounded separately. Thus, the efficiency of the entire protective system increases, especially when the zero wire fails.