What is the danger of self-grounding in the apartment (alteration TN-C to TN-C-S)

In the operation of home wiring, the most important issue is the safety of the operation of household electrical appliances. Grounding of electrical wiring is the main way to minimize the impact of electric current on a person in the event of a life-threatening potential on the metal case of household electrical appliances.

The problem of the lack of grounding in the apartment or in the house is quite common due to the power supply from outdated TN-C configuration networks in which the grounding of home electrical wiring is not provided.

To solve the problem, proceed as follows - ground the electrical wiring through the alteration of the TN-C system to TN-C-S. As a result, improper grounding of the wiring makes the operation of the wiring even more dangerous than in the absence of grounding per se. In this article, we will consider the danger of independent grounding through the alteration of the TN-C system to TN-C-S.

To understand the essence of the issue under consideration, we consider what the networks of the TN-C and TN-C-S grounding systems are.

In the TN-C system, the working neutral conductor N and the protective earth conductor PE are combined in one wire along the entire line from the transformer substation to the consumer - the so-called PEN conductor. Moreover, this combined conductor is brought into an apartment or a private house without separation into zero working and protective conductors.

Often there are recommendations regarding the protection of household electrical appliances by means of grounding - connecting the grounding pin in the socket to the PEN zero conductor combined. In this case, when a phase voltage appears on the housing of a household appliance, a short circuit will occur and the circuit breaker in the distribution panel will turn off.

The main disadvantage of grounding is that in case of a break in the neutral wire From the home switchboard to the place of grounding, phase voltage will appear on the equipment cases.

The same thing will happen in the event of a break in the neutral wire from the transformer substation to the entrance to the house - the phase voltage of the mains is guaranteed to appear on the body of the zeroed equipment.

In this regard, neutralization in the TN-C network is prohibited. That is, such a system in everyday life is operated as a two-wire system - only phase and zero working conductors are used to power electrical appliances.

The TN-C-S system differs from the TN-C system in that the combined PEN conductor when entering the building is divided into working zero N and protective PE. In this network, as well as in the TN-C network, a dangerous potential will appear on the grounding conductor in the event of a break in the combined PEN conductor to the separation point.

Therefore, to prevent the negative consequences of a zero loss in the TN-C-S configuration network, according to the EMP, requirements are made regarding mechanical resistance to damage to the PEN conductor on the power line, the organization of reliable repeated grounding of the PEN conductor, as well as the reliability of the PE ground bus directly in the house.

Only if these requirements are met, can the electrical network be operated as a TN-C-S configuration network, that is, use a protective conductor PE to ground the home wiring.

The main mistake in self-grounding is that the TN-C system appears simply as a TN-C-S system in which there is no separation of the protective conductor. In this case, the alteration of the TN-C system to TN-C-S is reduced to simply separating the combined PEN conductor into the working zero N and protective PE in the main distribution panel. This does not take into account the current state of the supply network.If grounding is not initially provided for in this network, then it is highly likely that the reason is that the electrical networks do not meet the requirements of the EMP.

Firstly, this is the technical condition of the electric network - if it is unsatisfactory, then there can be no talk of any mechanical resistance to damage to the PEN conductor. Secondly, the absence of a sufficient number of repeated grounding of the neutral conductor on the line even more increases the chances of the appearance of a dangerous potential on the grounding conductor that will arise as a result of a zero break on the line. That is, in this case, self-made grounding will be a source of danger for residents operating grounded household electrical appliances.

In this case, there are two options. The first option is to continue to operate a two-wire wiring, that is, without grounding before this problem can be solved by bringing the technical condition of the supply networks into line with the requirements for the TN-C-S network according to the PUE.

The second option is to switch to grounding system TT, that is, to make an individual grounding circuit, and use the combined PEN conductor of power supply networks only as a working neutral wire N. This option is relevant for residents of private houses or for residents of ground floor apartments who have the option of installing an individual grounding circuit for electrical wiring.

Comments

[#1 Woody]

The transfer from the TN-C system to the TN-C-S system is possible only with the modernization of the public house network. Such work can be performed either by the service company or by a third-party company that has permission to carry out such work, under the control of the service organization. Independently (for residents), system modernization is not possible. Particular cases of organizing the TT system locally are possible, but for this it is necessary to make a ground loop, while regularly monitoring its integrity and the absence of third-party connections. The transition from TN-C to TN-C-S is a comprehensive re-equipment of the entire network, and not just one point of it. Well, protective grounding is not a potential equalization system (SOE), although everyone believes that if there is a yellow-green wire, then this is earth, and therefore the SOU. That is why electricians should be wiring and connecting cables in the electrical panel, and not sellers of cosmetics and hairdressers.

[#2 Alexei]

I have such a story. When you touch a radiator or a sink in the kitchen, it is shocking. Not much, but noticeable. What is it? Improper grounding by any of the neighbors? Or just someone stealing electricity, using batteries and sinks as zero?

[#3]

The article is helpful. Especially for beginners.

And I have a wish: in connection with the widespread use in everyday life of devices with switching power supplies (computers, chargers, LED and energy-saving lamps, etc.), the article on filters at the input of analogue radio devices (HF receivers, etc.) would already be appropriate.
And then turn on the HF receiver to rummage around on the air - and there is a rumble!

[#4]

The TN-C-S system is a TN system in which the functions of the zero protective and zero working conductors are combined in one conductor in some part, starting from the power source. (PUE 1.7.3)

Power supply of electrical installations with voltage up to 1 kV from a source with a grounded neutral and with grounding of open conductive parts using an earthing switch not connected to the neutral (TT system), allowed only in caseswhen the electrical safety conditions in the systemTNcannot be provided. (And this must be proved !!) To protect against indirect contact in such electrical installations, an automatic power off must be performed with the mandatory use of RCDs. In this case, the condition must be met:

RaIa <50 V

WhereIa - response current of the protective device;

Ra -   the total resistance of the grounding conductor and the grounding conductor, when using RCDs to protect several power consumers - the grounding conductor of the most remote power receiver. (PUE 1.7.59)
The author of the article did not finish the first rule. Both circuits must be combined using 1 transformer left.
TT system prohibited !! I constantly correct the TT system for electricians, and they themselves do not know about it (that this TT system) and constantly disconnect the PEN conductor and PE.
Aleksey, because of the lack of a potential equalization system at the entrance to the building, it’s possible that the electric substation can be far away.

[#5]

Very useful and informative articles !!! Thank you that you are, that there is such a site. I do not regret that when I signed up!

[#6]

In my floor shield, the zero wire is connected to the metal housing of the shield. Is this correct and what is the name of such a system? Are the shield enclosures grounded? The house of the Leningrad series, a five-story building, built in 1977. Thank you in advance for your reply.

[#7]

Little is understood, and completely useless, because in such matters absolute clarity is needed.

[#8]

When repairing an apartment or house, you must complete 1 point of the PUE. That is, the wiring should be 3-wire. In this regard, the question arises: where to connect the working conductor (N) and the protective conductor (PE). Nobody will drive a special PE wire. In the riser on your site are usually 3-phase and PEN - conductor. It must be disconnected on PE and N - conductors. That is, in some part of it, to implement the TN-C-S system, this is your apartment. I do this: PEN is a conductor in old houses, it breaks at each site, it is necessary to connect it to the "0" bus, which in turn is mounted on metal. shield with screws. This is the PE bus, N cable goes from it to the opening two-pole machines of all apartments, the second pole is the phase. Further, counters and automatic machines leaving for apartments with a separate bus "0" for each apartment.
Repair must begin from the 1st floor !!. Everything in the shield, except for the counters, must be dismantled and discarded. I can throw a sample before and after on soap. Here I do not know how to download it.

Caution !!: Keep in mind that not every electrician will do the right thing for you (1% of 100%). Regalia - energy sales, the electricity network will not help. On duty, I carry out visual and instrumental control in electrical installations and I know what I'm talking about; In the power panel, check the PEN conductor for connection quality. All conductors must be connected individually .; If you break the PEN conductor without turning off the staircase, then at best it will burn equipment on other floors, and in the worst case, a fire! If you are not an electrician, don’t even take it !, everyone should do his own thing.

George,
In your old apartments, you have a TN-C system, but it’s hard to say whether it is right or wrong. For 1977, right, but for 2017 ?? In the apartment 2x - wiring or 3x - wiring? How is the PEN conductor connected?

[#9]

Andrew,
You are one of those cool experts of that level who PUEs write (I’m more about the Lithuanian rules, I noticed earlier that we are simply deducted from others). Alas, what is written in the PUE does not help, but hinders the understanding of what's what. There is no benefit from learning by heart, and it is impossible to learn because there is soooo thick and contradictory rubbish. I dug myself up to the level of understanding when I had to decide how to do it in specific cases.Everything is much simpler than the pue confuses and as long as they are not rewritten so that it is clear to the reading non-electrician, until then only one out of a hundred electricians will do it right. It used to be problematic with descriptions. Now you can already find descriptions in different languages ​​in which everything is clearly stated.

Is a person doing repairs in his apartment will remodel the whole staircase and further down to the power plant. We must trust what has been done by others in their area of ​​responsibility, and do it ourselves so that others can trust.

At the entrances, the PEN passes by wire and metal structures. It is duplicated and this is enough. PE and N differ in that a current flows through N and therefore burning of contacts is possible, as a result of which an increase in circuit resistance is possible. According to PE, the operating current does not flow, therefore it is always in the best condition in anticipation of an emergency in order to receive current from metal cases and ensure reliable operation of protective devices. Therefore, in places where PEN is divided into PE and N, they cannot be connected together to the same bolt or terminal. They must be connected separately to the same bus or design.

The leakage current relay performs its function in both two-wire and three-wire wiring. The difference is that with a three-wire it will turn off the network as soon as the leakage current appears on the equipment case, and with a two-wire it will have to be passed through it, which is not very nice :).

A voltage check between the PEN and L1, L2, L3 in the stairwell can indicate the status of the PEN circuit. If at least one voltage is much higher, and between the phases is normal then it is better to immediately contact the organization serving the electrical equipment at home.

[#10]

siGis,
In many ways you are right. PUE is a departmental document, this is a summary of GOSTs collected in one book. GOSTs have the force of law and are probably written off (adapted) from the IEC (International Electrotechnical Commission), it includes 60 (as of May 2016) countries of the world including Russia. I did not find either Lithuania or the Baltic countries there. Perhaps we have different standards and are better written. Not in vain we go to the Latin alphabet in the notation, these are the initial letters of English words.
The RCD of the RCD is prohibited in the TN-C system, but, in the next paragraph, if it is necessary to use an RCD, the protective conductor must be connected to the circuit breaker.
Regarding the “Checking the voltage between PEN and L1, L2, L3 in the stairwell”, I upgraded the power shield of the house (100 apartments), changed the inserts to automatic machines, after switching on the phase difference was L1-80A, L2-20A, L3-25A . Moreover, this was done back in Soviet times. Nobody will come to correct this with us. Especially an electrician from the housing office.
The condition of the old 5 floors is such that when repairing apartments, it is difficult not to upgrade the shield on the floor, at least partially.

[#11]

I wonder what caused the prohibition of RCDs in the TN-C system. Why is it forbidden in one paragraph and already allowed in another. It turns out, as it were, not prohibited. As you need to understand the requirement, the protective conductor (PE probably) will connect to the machine. Is it different. In my opinion, even with the advice it was forbidden to put fuses on the neutral wire. Maybe the writers mean that the separation of PEN into PE and N cannot be done at the output of the RCD, but they themselves did not fully understand what they wrote something incomprehensible.

[#12]

siGis,
It is forbidden because there is no third wire (PE). But, if you connect, say, a washing machine with three-wire (!), Then you connect the RE-conductor to the machine, and the machine is 2-pole, input separation. The output of the automaton L and N to the RCD, it is necessary to choose an automaton with double contacts, or as you and I described, for individual contacts this is a requirement of GOST and IEC. That is, PEN comes to PE and there it is divided into N, all contacts are connected individually on the bus "0". The presence of switching devices to the PE and N buses is prohibited, this is obvious.But for L and PEN or L and N - 2-pole is allowed.

[#13 MaksimovM]

Andrew, you write “TT system is allowed only in those cases when the electrical safety conditions in the TN system cannot be provided. And this must be proved. ” There is no need to prove anything to anyone. If it is visually evident that the line is in unsatisfactory technical condition, there are no repeated grounding of the combined conductor, inspections and revisions of the lines are never carried out, then such a network will not only not provide electrical safety, but will also be a potential source of danger. To exploit the grounding of electrical wiring in this case is to endanger the life of your family.

You are talking about fulfilling the PUE requirements regarding grounding of electrical wiring by implementing the TN-C-S system, but you forget about the most important thing - the PUE requirements for networks. If the sufficient mechanical strength of the PEN conductor is not ensured and the required number of re-earthing is not available, then such a conductor cannot be used to ground the wiring. This is what the article discusses - the danger of altering the TN-C configuration network to the TN-C-S network. You can not give unreasonable advice regarding the grounding of electrical wiring by separating the PEN conductor without having information about the state of the power supply network.

siGis, The TN-C system itself is banned in domestic wiring, since grounding is dangerous. Such a system must be operated only as a two-wire, that is, without a protective conductor. And if we consider a two-wire network, then I think that it is necessary to put an RCD in it in any case, and if in some regulatory documents there is a ban on its installation, then it is not justified. The residual current device is an additional measure of protection against electric shock, both in the presence of grounding and without it. The RCD will provide protection against direct contact with the phase conductor, for example, in the event of a breakdown on the housing of a household appliance.

[#14]

MaksimovM,
I did not understand your first paragraph. How to implement a TT or TN-C-S system in a multi-story building, that is, leave everything as it is.
Re-grounding is advisory. "When applying the systemTN recommended re-groundPE-andPEN-conductors at the entrance to the electrical installations of buildings, as well as in other accessible places. For re-grounding, natural grounding conductors should be used first. Resistance of a grounding conductor of repeated grounding is not standardized. PUE 1.7.61"
I check the electrical installations of our city (for example, boosting stations) from 26 pcs. Grounding have only new 4 pcs. With old residential buildings the same thing. Two of these I serve. One entrance was replaced with five-wire without grounding, although the substation is nearby.
With the TN-C system, the casings are zeroed, see the beginning of the article. Is TN-C-S worse? If you replaced the wiring in the apartment, naturally, with 3-wiring, where do you connect the green-yellow conductor? With TN-C system, the housing must be zeroed. And if you connect the washing machine with 2-wire and the network potential appears on the case (there were cases) then there will be "fun".
I give advice because I have practical experience. Write how you are doing apartment renovation in a high-rise building. Or in homes.
Right now I am doing repairs in the courtyard, of course, with 3 wires, without access to the power panels of the house. This is for the dagger.
 

[#15 MaksimovM]

Andrew, I meant that if the power supply line does not meet the requirements for TN-C-S networks, then, accordingly, when the combined conductor breaks to the place of its separation on the housings of household electrical appliances, a dangerous potential will appear, and with serviceable electrical appliances. Grounding electrical wiring in this case will be a potential source of danger.

As for the repair of an apartment in a high-rise building, in any case I will give preference to a three-wire wiring, since the wiring is mounted for a long time. But I will immediately connect the grounding conductor only if I am sure that the line is in normal condition. Otherwise, I’ll leave the conductor until the grounding in the house is implemented in accordance with the requirements. If possible, you can mount an individual grounding circuit and ground the wiring (TT system). No more options.

The TN-C system is operated exclusively as a two-wire system, since grounding is not allowed at home.

[#16 Stepan]

Nobody canceled the laws of Kirgoff !!! With the right connection, everything should work.

[#17 Sergei]

Today, the sales refused to seal the meter in the apartment, because of the third input core. Type can be unaccounted for by this vein.
Proposed to unite on the opening two-pole machine:
1 pole N + PE
2 pole L
I do not do this, for a number of reasons known to all.
Once he made one, and he himself fell into a trap, the landlord changed zero and the phase at the input or in the expansion box, shook so that he stuck for a minute, he could barely come off, rested his foot on the wall and fell.
Such dark clouds were already spinning in my head, and my thoughts were sad.

[#18 Alexander]

siGis, 

what is the reason for the prohibition of RCD in TN-C

Reported Injuries when the RCD trips. The possible non-synchronization of the opening of the RCD contacts and the opening of the N-contact first (zero break!), And after a small potential leakage to the case, the touch of which provoked the operation of the RCD, is already beating a phase current. Let only for a moment - 20ms. For a wet, steamed body, current and time are enough ...
Therefore, a ban. With the reservation in the next paragraph - with connecting Re to N in front of the switch (that is, by grounding, connect Re to the input N-terminal of the RCD). This loop should be as short as possible so as not to interfere with the operation of the RCD.