Zanulenie is a measure to prevent a person from being electrocuted by electrocution, which consists in combining the conductors of an installation that are not in a normal state under voltage with a neutral.
. Basic Terms and Definitions.
. It is accepted to call a “nullification” protective, in order to uniquely distinguish it among other conductors. In electrical engineering of three-phase circuits, it is customary to call the circuit section the effective voltage on which is equal to the external windings. When equalizing the potential with the earth, the current here does not flow normally. This applies to the supply side of the source( transformer substation), consumers( motors).The grounded neutral is called the zero point. Hence the term considered by the topic.
Zeroing methods are highly dependent on the network arrangement. Single phase or three phase as grounding. According to the latter factor, it is customary to distinguish three types of systems. According to tradition, the international committee of the IEC, they are marked with Latin letters:
- TN;
- TT;
- IT.
The ZD-
System. The second letter is of interest:
- N means that the conductive parts of the installation, which are not normally under current, are zeroed through the protective( dedicated ground) or working conductor. In the first case, the segment of the wire is directionally used for safety purposes, in the second - it serves to close the circuit to the ground( near the transformer), as, say, in the TN-C network.
- T - indicates the presence of grounding parts of the installation, in normal mode, the current is not current, but possible sources of danger in the event of an accident. The difference from the zeroing, marked with the letter N: N is considered to be neutral, passing an extremely small current to earth. If the body of a three-phase installation is directly connected to the circuit, say, a lightning rod, the current( and danger) will increase greatly when the potential is removed.
For single-phase circuits, the difference between zeroing and grounding is leveled for obvious reasons. But! The scale of the apartment building is preservedA high-rise building is considered as a three-phase electrical installation. Consequently, it is necessary to continue to consider the situation, because there are a number of ways to organize grounding and zeroing. This is evident in practice when the authors of the topics try to explain what TN-C, TN-S, TN-C-S are.
What are TN-C, TN-S and TN-C-S
The letter C means that the protective and working conductor are combined. Such a system is good for three-phase equipment, and zeroing is always possible, saving you from trouble. They write on the Internet, they say, backward and bad system, which is fundamentally wrong. For three-phase equipment, this is a good and correct system, zeroing the case and other conductors, the master unloads the grounding circuits in advance, one of which is unintentionally capable of becoming man. Which naturally reduces the risk of accidents.
Bad TN-C systems exclusively for imported technology, for a trivial reason: household appliance input filters are designed to work with individual protective conductors. It is supposed to protect the network from interference. The TN-C or TN-C-S knowledge system solves some of the difficulties, but violates the symmetry of the filters, which negatively affects the quality of work. Imported equipment( the lion's share) is designed to work in TN-S.The main difference of the approach:
- It is assumed that there are no three-phase consumers in the local network. Consequently, the zeroing of the body does not carry much physical meaning. It is equivalent to grounding.
- The protective( differential) automata are built so that they catch the difference between the phase and neutral conductor currents. Consequently, any leakage to earth is localized, the power is turned off.
To adapt the described system at the level of the Soviet TN-C decided to modify the old under the TN-C-S.Now any leakage goes to neutral through the circuit of the lightning rod, but the automatic differential protection is placed in the circuit of the working neutral conductor. Accident invariably seen. An additional advantage of using the TN-C-S system is the possibility of including three-phase consumers( elevator engines, for example) into the circuit according to the old proven scheme. The main disadvantage has already been named: violation of the correct operation mode of the input filters of imported equipment.
The only difference between TN-S and TN-C-S: in the area of the lightning rod, the protective neutral conductor( ground) is combined with the worker( coming from the substation).If you want to go completely to the European standard, you just need to correct this point. Do not connect the wire from the substation to the local ground loop dug in the basement area. The work of three-phase equipment can be disrupted, in the sense that a situation of voltage output to the body, potentially dangerous for humans, becomes potentially realizable. The operation of the electrical installation is not disturbed( with a high probability).Consequently, the accident will go unnoticed until the installation is touched by a person with the ensuing consequences.
Grounding systems and zeroing
The letter T, which stands in the first place, means that the working conductor is grounded, I - that it is isolated from the ground. The latter is often used, for example, in systems of ultra-low safe voltage. These are used( according to GOST R 50571.11) in bathrooms and other similar in purpose premises. We are talking now about an isolation transformer, not a single point of the secondary winding of the device is grounded( otherwise, the sense of using this protection measure is lost).
It is easy to understand that to solve practical problems it is required to study the theory. This can be seen in the above example with a bathroom. Electricians have typical errors, but in the context of this review, grounding systems are considered that are closely related to zeroing. Systems with isolated IT neutrality were once considered dominant in Europe. Zanulenie in this case does not apply. Or on the side of the source, without having to do with the consumer.
The need for grounding arose in the decades when broadcasting and television were actively developing. It turned out that without connecting the screen with the ground, part of the waves pass through the shield. And this interference and large energy losses. Consequently, devices on the consumer side began to need grounding( and zeroing).Among other things, when the radio wave( including the 50 Hz network frequency) goes on the air, the person affected by it receives damage to health.
Distinction between
systems. Local grounding( solidly earthed neutral) is possible only when the load on the phases is symmetrical. Then only a small current goes to the ground. In the case of high-rise buildings there is no talk of symmetry, the neighbors will not agree to jointly turn on the first devices and turn off the second. It is too expensive to close the circuit of the supply transformer through the soil. This would lead to potentially dangerous situations( see step voltage), increasing losses by orders of magnitude. As a result, there is a need for neutral: a typical case, when 4 wires go along a pole, only three - phase.
Particular attention is paid to the vanishing of microwave ovens. To implement this measure, in houses with TN-C systems( the overwhelming number of houses built in the USSR), neutral should be displayed on the side lobe of the outlet. To perform the operations correctly, it is recommended to use indicator screwdrivers. The houses, rebuilt in the previous era, are equipped with grounding branches. And the system turns into TN-C-S.Often, people do not understand the meaning of this measure, and therefore there are incorrect interpretations. Briefly: the neutral of the three-phase network at the entrance to the building is electrically combined with a lightning conductor buried in the ground. From here begins the local branch of grounding, diluted by apartments.
In the topic about protective grounding, it was discussed how the zeroing differs from the mentioned measure( it is necessary all the time).The neutral is electrically connected to all phases, and return currents circulate here. Only a part of it goes to the ground, and with an imbalance. Grounding without zeroing is dangerous. This explains the presence of the TN-C-S system versus the TN-S.In the latter, the protective and working neutral conductors are separated along the entire length. If it is not intended to use three-phase installations, it is good, otherwise what has already been told will happen( see protective grounding).
In order to avoid the presence of dangerous potential on the body of equipment in the area of the lightning rod, merging with a neutral is required. Metal parts, which a person can hypothetically take up, are grounded short: mainly pipes. The presence of a protective conductor combined with a neutral in the area of a lightning rod or a local separate circuit dug into the ground( instead of direct grounding) reduces the current in the specified branch and additionally protects the person if, for some unknown reason, the protection circuit breakers do not work.
What you need to nullify, and that you can not nullify
For domestic purposes, it is not recommended to zero everything that was previously grounded through pipes: cast-iron baths, metal sinks, mixers. Known story Zadornov, as the shower was beating with current when the TV is on. A clever man decided to ground himself when the body was zeroed. Suppose pipes are wound to neutral. When the device is turned on, the current will be divided between the working neutral conductor and the grounded pipes. Part of the current passed through Zadornov, summed up with a jet of water.
Simultaneous zeroing and grounding is effective exclusively for three-phase circuits. And with a symmetrical load on each shoulder. As for equalizing the potentials of all metal objects in the kitchen, in the bathroom, the toilet, it is better to use grounding for these purposes. In the case of metal pipes, it is sufficient to connect the indicated objects with copper wire. Neutral start here is not necessary in connection with the described features of the single-phase circuit.
Let us mention the case of a microwave case vanishing. Large capacity in the operating mode is not expected here, as is the case with a washing machine. According to GOST R 50571.11 one of the protection measures is selected differential machine. If an electric shock occurs, the equipment will be turned off. The parameters of the differential protection machine are pre-calculated so as not to cause harm. GOST specifies the minimum response current and other physical quantities.
It is useful to remind that it is impossible to zero or ground anything through pipes and other communications. But these structures are permissible to protect. In production, this requirement is mandatory, to prevent the cases described above, machines are installed that turn off the network in the event of a malfunction.
