Exploring the Use of RCDs in TN-C Installations: Old Buildings, Two-Wire Power Supply, and More

Hello.

First...
I read the forum and I wonder why the theorists are probably mainly against the use of RCDs in TN-C installations.
I do not want to discuss normal and regulations because I know what they are, but also everyone knows what they used to be in the past.

Suppose we have an old building, the power is supplied by two wires (TN-C standard) phase and PEN earthed by power plants.
In this old house we have old sockets without a grounding "pin", and, for example, several with a pin connected to the PEN conductor. (Two wires everywhere).

I understand that the regulations and standards say that the RCD in such an installation is evil, but for a common sense, it seems to me that the RCD does more good than evil here.

When we connect a device of the first class of protection to a socket without a grounding "pin" (I know you must not, but explain it to older people, for them this socket and this socket), without an RCD, we do not have any protection in the event of a breakdown on the housing, and after assembly Although the RCD has minimal protection, in the event of current leakage to the chassis and the human RCD should turn off the power.

I understand the regulations, but it is probably better to be protected by an RCD in this way than to be protected only by a 16A fuse. :-)

I am writing this because I see that the forum is followed by people who have used RCDs in the TN-C installation.

After all, the RCD does not pose a direct threat to life in such an installation, it can give a slightly illusory sense of security, but it increases it anyway in relation to the lack of an RCD.

A question for those who know, is there any reason why RCDs should not be used in TN-C and this reason is directly life-threatening?
Can you confirm that the RCD in TN-C gives no advantages?

I myself have seen systems where half of the old building (you can say factory) was in the TNC system and there were RCDs and these switches actually worked in practice, and the other half were only renovated to TN-S.

Next....
I read a few topics where people asked about minor things, a small renovation of the installation in the OLD house and the "specialists" came to them for not having separate over-current switches for each socket.
Don't you think it's a bit sick?
I understand the implementation of standards in new construction, but if someone does a SMALL renovation and tries to slightly improve the installations, he will probably not get help in this forum, because they tell him to replace everything and everywhere :-)

There are hundreds of thousands of houses in Poland where 20 sockets work on one phase with the old "plug" and there are no problems with it, and if someone wants to improve something, it would be appropriate to help him as much as possible, and not to criticize "no because no", the standard says ...

Even a layman like me is able to accept the dogma that installing a fuse on the PEN wire can disconnect this circuit and it will be very bad

r103 wrote:

Even a layman like me is able to accept the dogma that installing a fuse on the PEN wire can disconnect this circuit and it will be very bad

Why would it be bad if all the wires in the RCD are disconnected and not just one.

Disconnecting the PEN, of course, is dangerous, but the watchtower does not protect against it, nor does it.
Of course, we ignore the fact that the installation of the RCD in such an installation may cause its accidental actuation.

kryst16 wrote:

Why would it be bad if all the wires in the RCD are disconnected and not just one.

And you know a camera that guarantees it 100%, I repeat 100%?

Exactly. In this case, it qualifies as damaged, as well as the one who sleeps, which has a shutdown current above the rated one, etc.
Besides, I am curious why rcd is not produced with a non-detachable N track

opornik7 wrote:

kryst16 wrote:

Why would it be bad if all the wires in the RCD are disconnected and not just one.

And you know a camera that guarantees it 100%, I repeat 100%?

Nothing is 100% guaranteed, but in general the RCD is so constructed that it shouldn't disconnect only one wire, sooner it won't trip in general than disconnect one.

Sooner the wind will break one line from the pole and it will be PEN than the RCD will switch it off.

Is that why the use of RCDs in TN-C was banned or because it does not fully fulfill its role in this installation, giving a false sense of security?

It cannot be used for protection against electric shock, whether basic or additional, which in a TNC or non-classified installation does not protect against electric shock at all.
The duty is to protect against electric shock, and in this situation the RCD will work or not, but always after the electric shock.
Secondly, no one has yet come up with protection when the installation is used contrary to its intended use (connecting devices that require a protective contact to a socket without such a contact).

Rather, no one will simply confirm that the use of RCDs in TN-C is harmful, I consider it unnecessary overzealousness (after all, in TN-S, not all circuits are protected by RCDs).
The problem is that the TN-C RCD does not meet the requirements necessary to operate fully as intended.

kryst16 wrote:

is it because it does not fully fulfill its role in this installation, giving a false sense of security?

I think this is one of the reasons.

Turysta_ wrote:

Rather, no one will simply confirm that the use of RCDs in TN-C is harmful

I believe that the use of sockets with a protective contact and zeroing provides better protection.

Everything is clear to me about this. Put together a few rules and facts and no one will have any doubts.

1. The PEN acts as a protective conductor.
2. Protective conductors must not be disconnected, disconnected, etc. along their entire length. They are to be continuous throughout their length.
3. RCD disconnects both the phase and the circuit N.
4. By connecting the PEN conductor to the N track, you connect the protective conductor to it, so when the RCD is in a state of breaking the electric potential, you break the rule that the PE conductors must be uninterruptible.

The end and the PERIOD.

I am an engineer, but an amateur electrician. I am not going to make any modifications to the installation myself. I am writing this post solely out of the desire to learn about the issue and the need to supervise an electrician at work. Correct me if I am writing nonsense.
In the rest of my post I will use the RCD1 and RCD2 markings.
- RCD1 means a "normal" RCD in the distribution board connected to the L and PEN conductors
- RCD2 means RCD inserted into the socket, i.e. something like "Elgotech Network Adapter With Residual Current Device (Tfga-1F)" connected in the socket to the L and N conductors (I suppose PEN is separated into PE and N in front of the RCD circuit itself)

In the case of a TNC network, we can have the following electric shock scenarios:
1. LN -> nothing will help here
2. L-PE -> RCD2 should trip
3. L-ground (i.e. "the child puts the wire into the socket") -> RCD1 and RCD2 should work
4. voltage on the casing due to damage to the PEN -> RCD1 may work

In the above cases, as can be seen, the safety increases after using the RCD.
The regulations stipulate that in TNC networks, the RCD does not constitute electric shock protection, but it does not follow from this provision that the RCD must not be used.

The downside of using an RCD in a TNC may be the ejection of the RCD when you touch the housing of a device such as a washing machine, refrigerator, etc.

aare wrote:

I am an engineer, but an amateur electrician. I am not going to make any modifications to the installation myself. I am writing this post solely out of the desire to learn about the issue and the need to supervise an electrician at work. Correct me if I am writing nonsense.
In the rest of my post I will use the RCD1 and RCD2 markings.
- RCD1 means a "normal" RCD in the distribution board connected to the L and PEN conductors
- RCD2 means RCD inserted into the socket, i.e. something like "Elgotech Network Adapter With Residual Current Switch (Tfga-1F)" connected in the socket to the L and N conductors (I suppose PE is separated into PE and N in front of the RCD circuit itself)

In the case of a TNC network, we can have the following electric shock scenarios:
1. LN -> nothing will help here
2. L-PE -> RCD2 should trip
3. L-ground (i.e. "the child puts the wire into the socket") -> RCD1 and RCD2 should work
4. voltage on the casing due to damage to the PEN -> RCD1 may work

In the above cases, as can be seen, after using the RCD, the safety increases.
The regulations stipulate that in TNC networks, the RCD does not provide protection against electric shock, but it does not follow from this provision that the RCD must not be used.

The downside of using an RCD in a TNC may be the ejection of the RCD when you touch the housing of a device such as a washing machine, refrigerator, etc.

I am of exactly the same opinion.
RCD is okay and can help.

masonry wrote:

It cannot be used for protection against electric shock, whether basic or additional, which in a TNC or non-classified installation does not protect against electric shock at all.
The duty is to protect against electric shock, and in this situation the RCD will work or not, but always after the electric shock.
Secondly, no one has yet come up with protection when the installation is used contrary to its intended use (connecting devices that require a protective contact to a socket without such a contact).

Well, explain it to people who have been plugging everything normally into pinless sockets for years, whether they are washing machines or refrigerators in old buildings.
It makes no difference to them.

In TN-C it is better to be electrocuted with a current of 30mA than much more, so for me the RCD even in the TN-C has a lot of advantages.

Voldi123 wrote:

Everything is clear to me about this. Put some principles and facts together, and no one will have any doubts.

1. The PEN acts as a protective conductor.
2. Protective conductors must not be disconnected, disconnected, etc. along their entire length. They are to be continuous throughout their length.
3. RCD disconnects both the phase and the circuit N.
4. By connecting the PEN conductor to the N track, you connect the protective conductor to it, so when the RCD is in a state of breaking the electric potential, you break the rule that the PE conductors must be uninterruptible.

The end and the PERIOD.

It's a pity it's all so theoretical.
When the wind breaks the PEN lines, you will also tell him that the standard says that he could not break?

I am interested in how the RCD would behave in the event of a break in the PEN line and a current leakage above 30mA from the phase to the housing of the device and a person. I think the RCD should work in this situation which is another plus.

I think that there are no logical and strong contraindications for installing RCDs in TN-C systems because, after all, it will not increase the risk of electrocution.

15kVmaciej wrote:

kryst16 wrote:

In TN-C it is better to be electrocuted with a current of 30mA than much more, so for me the RCD even in the TN-C has a lot of advantages.

Buddy, you are assuming a situation when someone has to touch a washing machine with a housing on the housing and the RCD is to save his life.
Take note that first of all, not 20, not 30mA will flow through the delinquent, but as much as the quotient of the voltage and the resistance of the delinquent's body.
For, and this is also the second thing, we expect from RCDs to limit the time, not the current, first of all. And the time required for the RCD reaction is 200msec, which is ten periods for 50Hz. Maybe ventricular fibrillation will not occur, but kick up healthy and scare even lethal. But if you know more and better than me, experiment with your own grandma, for others, I sincerely advise against testing the differential with your own body. It really can be a lot more than 30mA, best regards

Electric shock in an installation with a functional RCD is not dangerous to human life, I am talking about it here.
The discussion is about the practical benefits of an RCD in such an installation, not the theoretical one.

And even in this hypothetical situation, it is better for it to take place in a house with an RCD than in a house without an RCD, because with RCDs, the chances of survival are much greater.
After all, with a working RCD you will barely feel this current.
I just want to say that writing that an RCD in a house where the installation is in TN-C technology is not a catastrophe and gives a certain amount of safety.
I am talking about a practical situation, not what the standard says ...

kryst16 wrote:

Saying ugly, you have ever been hit by electricity from an installation in which there was an RCD? Yes, and I barely felt it, you know fear, but it does not kill and the RCD tripped.

Buddy, to discuss this topic in a matter-of-fact way, you must understand a few basic things about electrics.
One of them is that what you felt during the shock had nothing to do with whether the RCD was in the installation or not.
Unfortunately, laymen are not able to understand this and that is why such strange theories arise.

kryst16 wrote:

RCD in such an installation

The basic question is why throw away PLN 100 and install such a thing and pay for the service if it is unnecessary and not recommended.

Added after 1 [minutes]:

kryst16 wrote:

When the wind breaks the PEN lines, you will also tell him that the standard says that he could not break?

The PEN is repeatedly grounded at multiple points. Moreover, the 3-phase installation itself produces a voltage close to 0V depending on the load.

kryst16 wrote:

It's a pity it's all so theoretical.
When the wind breaks the PEN lines, you will also tell him that the standard says that he could not break?

I am interested in how the RCD would behave in the event of a break in the PEN line and a current leakage above 30mA from the phase to the housing of the device and a person. I think the RCD should work in this situation which is another plus.

I think that there are no logical and strong contraindications for installing RCDs in TN-C systems because, after all, it will not increase the risk of electrocution.

Theoretical !? You have 2 simple cases (I will explain it blatantly so that you understand):

1. In an old type installation, the neutral wire in the sockets is connected to the protective conductor. If there is a breakdown to the housing of the device and the current flows through the housing to the socket, then from the point of view of the RCD switch everything will be in the best order. The switch has no idea what's going on behind the socket. All he knows is that the amount of current that has leaked out matches the amount of current that has returned from the device. And since it flowed through the housing, it is difficult.
In summary: The RCD may not work when it should.
2. In a TN-C installation, the current flowing from the differential may not be consistent with the current returning to it. If you simultaneously touch (by yourself or with some conductive element), e.g. the computer housing and the radiator, the potential equalization may occur (the central heating installation may be better grounded) and the circuit breaker will trip because some of the current has "escaped". '
In summary: An RCD may trip in a situation where it should not.

And now tell me: is it fun to live with a differential plugged in, which won't really work when it should, but will work when it shouldn't?

Oh, I like theorists.

It is enough that the refrigerator or washing machine or anything else will have a potential of the housing other than the environment in which it is located and the equalizing current will flow to the ground and it will trigger a differential differential at random.

This potential will result from the network load and is random.


Has it arrived now?

Do you really have no idea about electrical engineering and do you grow Joyful TFurosć / weekend shit in your installations or not?

Why don't you start overhauling the installation from the right side with the other.

Voldi123 wrote:

2. In a TN-C installation, the current flowing from the differential may not be consistent with the current returning to it. If you simultaneously touch (by yourself or with some conductive element), e.g. the computer housing and the radiator, the potential equalization may occur (the central heating installation may be better grounded) and the circuit breaker will trip because some of the current has "escaped". '
In summary: An RCD may trip in a situation where it should not.

The RCD will work if the current is greater than 30mA, so if I touch the computer housing and the radiator and it flows through my body 30mA or more, I prefer the RCD to disconnect me from the voltage.
In a functional computer, no more than a few mA will flow through the housing and the RCD will not turn off unnecessarily.

tantalos1 wrote:

if I touch the computer casing and the radiator and it flows through my body 30mA or more, I prefer the RCD to disconnect me from the voltage.

Under no circumstances is there to be a voltage on the accessible parts of the devices, which will cause the flow of a lethal current of 30mA.

tantalos1 wrote:

The RCD will work if the current is greater than 30mA, so if I touch the computer housing and the radiator and it flows through my body 30mA or more, I prefer the RCD to disconnect me from the voltage.

But you will get electrocuted. The computer has a plug in protection class. Better to have a socket with a protective contact and zeroing. In this case, when a breakdown occurs to the housing, the power will be disconnected by an overcurrent fuse.

rafbid wrote:

tantalos1 wrote:

The RCD will work if the current is greater than 30mA, so if I touch the computer housing and the radiator and it flows through my body 30mA or more, I prefer the RCD to disconnect me from the voltage.

But you will get electrocuted. The computer has a plug in protection class. Better to have a socket with a protective contact and zeroing. In this case, when a breakdown occurs to the housing, the power will be disconnected by an overcurrent fuse.

At what current will the reset protection trip?

tantalos1 wrote:

At what current will the reset protection trip?

With the one installed on the circuit breaker.

tantalos1 wrote:

rafbid wrote:
tantalos1 wrote:
The RCD will work if the current is greater than 30mA, so if I touch the computer housing and the radiator and it flows through my body 30mA or more, I prefer the RCD to disconnect me from the voltage.
But you will get electrocuted. The computer has a plug in protection class. Better to have a socket with a protective contact and zeroing. In this case, when a breakdown occurs to the housing, the power will be disconnected by an overcurrent fuse.

At what current will the reset protection trip?

It depends on the characteristic value of the fuse protecting the given circuit. The plus is that there is no need for an electric shock for the power to be disconnected and the 230V voltage will not appear on the housing

tantalos1 wrote:

At what current will the reset protection trip?

This question cannot be answered precisely.
It will trip at a current greater than the rated current of the protection device, e.g. 200A or maybe 85.66A.
In protection against electric shock, more important is the time in which the protection works and that it works before someone touches the damaged device, which the TNC's RCD will not provide.
There is no protection against the stupidity of inserting a nail into the socket or connecting devices in protection class I to a socket without a protective contact.

tantalos1 wrote:

The RCD will trip if the current is greater than 30mA,

That's not true.

In order for the fuse to work within 0.4 seconds, which is required in installations because time is more important, it will be 50A at B10 and at C16 it will be 160 and for this to be effective, the resistance of the short circuit loop must be sufficient.

And I suggest that a colleague krys16 experimented on himself.
Since he is so confident, let him sacrifice himself for knowledge, for science and finally for the electrode.
The results of the experiments are welcome on the forum.

elpapiotr wrote:

And I suggest that my friend krys16 experiment on himself.

He didn't even know where to start the experiments ... .