Redistributing 3 Phases for Multiple Appliances: 2 Refrigerators, Oven, Microwave, Radio

Good morning,

I need to redo the sockets in the apartment. Currently I have 3 sockets on one phase (3x2.5mm wire). Standard and typical installation as in new blocks (TN-S). I want to connect receivers to these three sockets: two refrigerators, an oven, a microwave and a radio. Of course, one phase can't handle it, so I have to modify it. I want to pull 3 phases from the switchgear and use them as follows: the first phase for refrigerators (ordinary household refrigerators), the second phase for the oven, the third phase for the microwave and radio. And now I come to the question part. Since there is little space in the switchgear, the cables are arranged tightly, can I replace the current 3x2.5mm cable with a 5x2.5mm cable and use one Neutral wire for all receivers? To clarify the question: what current can I expect on the neutral wire, unfortunately I cannot calculate it myself. Is such an installation a safety hazard or may it not function properly?

The current on the neutral is the geometric sum of the phase currents. It follows that the closer the load on each phase is to each other, the lower the total current on the neutral conductor. So if all three pradyys are equal then the geometric sum will be zero.

Such a system will work, and theoretically the current flowing through the neutral conductor should never be greater than the highest current flowing in any of the phases.
In the case of a 3-phase supply, if each of the phases is loaded with the same current, no current flows through the neutral conductor. Then the neutral wire is not needed.
In practice, the value of the current in the N conductor may be higher if the connected devices introduce phase shifts and additional harmonics.

Why just mix it up? Such a connection carries a number of problems, including damaging devices connected to 1-phase sockets, if the circuits are to be protected with a 3-phase differential. Unfortunately, such an installation cannot be secured with 1-phase differential circuits, and protection of this installation with one 3-phase differential circuit can damage devices powered by 230V.

wilk2002 wrote:

Good morning,

I need to redo the sockets in the apartment. Currently I have 3 sockets on one phase (3x2.5mm wire). Standard and typical installation as in new blocks (TN-S). I want to connect receivers to these three sockets: two refrigerators, an oven, a microwave and a radio. Of course, one phase can't handle it, so I have to modify it. I want to pull 3 phases from the switchgear and use them as follows: the first phase for refrigerators (ordinary household refrigerators), the second phase for the oven, the third phase for the microwave and radio. And now I come to the question part. Since there is little space in the switchgear, the cables are arranged tightly, can I replace the current 3x2.5mm cable with a 5x2.5mm cable and use one Neutral wire for all receivers? To clarify the question: what current can I expect on the neutral wire, unfortunately I cannot calculate it myself. Is such an installation a safety hazard or may it not function properly?

No combinations with 5x2.5 cable, separate single-phase circuits must be led out of the switchgear. Since the protection of a 3-phase cable will fit, it will also fit 3 1-phase protections.

I don't understand your way of thinking, how is connecting a three-phase RCD to damage devices? Damage to connected devices can only occur when there is a break in the main neutral. You just need to make sure that something like this can't happen and, of course, to choose the correct overcurrent protection.

As a colleague mawerix123 writes: if you have a renovation, you have a choice, so do it right.
If the switchgear is too small, replace it - immediately with a larger one...
Now you have a small problem, and if something goes wrong, then it will be a big problem.

Thank you for such a quick response, I will add a few sentences to dispel doubts and clarify the situation:
- the idea came from the fact that there are already so many wires from the switchgear that pushing the next two there is really problematic in practice. The laid wires would force them to be forged and repositioned to make room for new ones or, alternatively, to forge under the existing wires (in reinforced concrete :/) and pull the new wires crosswise under the existing ones. In short: it's dense.
- the whole question refers only to these three specific sockets (for the mentioned receivers), the rest of the installation is made in a boxless system "in God's way", i.e. each L has its N in one cable (3x2.5mm)
- in the switchgear at the input there is a three-phase differential with one N
- Wires (3x2.5mm) from different phases are run on the flat and all their N's are gathered in the switchgear into one rail. "Run from different phases" means that the L's are derived from overcurrent protections connected with a three-phase bus, so every third overcurrent protection has the same phase and such an installation is distributed around the apartment.
I hope this additional information clarifies the context, if I missed something please point it out to me.

xury wrote:

I don't understand your way of thinking, how is connecting a three-phase RCD to damage devices? Damage to connected devices can only occur when there is a break in the main neutral. You just need to make sure that something like this can't happen and, of course, to choose the correct overcurrent protection.

A 3-phase RCD also disconnects the N conductor. Dust, especially gypsum dust, bits of plaster often get inside. If such a particle gets between the N contacts, the "disco" begins. I don't think I need to write about the effects, because you probably know what's going on? I don't think I need to add that such a 3-phase differential does not even react to the lack of continuity of the N conductor, also on the contacts inside the differential.

For typical 3-phase devices, this condition is not a problem, because for such devices the N conductor is not needed for proper operation.
However, problems arise when 1-phase circuits are protected by 3-phase differentials.

These are not theoretical considerations, but I have encountered such situations many times. The last one was earlier this month. As a result of such a failure of the RCD, the electronics of the gas boiler failed.

Plumpi wrote:

These are not theoretical considerations, but I have encountered such situations many times. The last one was earlier this month. As a result of such a failure of the RCD, the electronics of the gas boiler failed.

Only the electronics of the stove - and the other receivers have not been damaged?
The electronics of a gas oven can be damaged for an unspecified reason.
These devices "have it".

CYRUS2 wrote:

Plumpi wrote:

These are not theoretical considerations, but I have encountered such situations many times. The last one was earlier this month. As a result of such a failure of the RCD, the electronics of the gas boiler failed.

Only the electronics of the stove - and the other receivers have not been damaged?
The electronics of a gas oven can be damaged for an unspecified reason.
These devices "have it".

Just the whole house is powered from a different box and from a different differential. Unfortunately, also 3-phase.
The differential that failed is in the boiler room and powers only the boiler room. If the whole house was powered from it, the losses would probably be higher.
The differential tube was probably finished off with dust and coal and ash dust, because previously there was a fine coal boiler used there.

Although I have not had contact with damage strictly by RCDs or 4-pole disconnectors, but once the connection from the differential circuit with the N outlet strip loosened after several years and there were losses in some equipment.

Dear Gentlemen,
thank you for your replies. Please help me understand them because I have doubts. Some of you wrote that I have to run 3 separate wires to the three sockets so that each socket has its own Neutral, but can you please tell me the reasons for this recommendation? If I don't do this, do you think I will damage the receivers now or in the future? Why, in your opinion, should I not pull 5x2.5mm and power three sockets from three phases, leading only one Neutral from them?

Others of you have pointed out possible problems with the three-phase differential. Only that let me point out that it would be a separate problem in the apartment, because this is exactly the installation that was provided by the developer in the apartment. There is a three-phase differential at the input with one N. And all three phases have been "randomly" distributed around the apartment, the overcurrent rail simply distributes the phases 1, 2, 3 in a cycle after overcurrent protection and in this way the phases go to the installation, from which all their N's are collected on one neutral rail, so already without any modifications of mine, the developer has provided in the switchgear such a scheme that Neutral wires from different phases are collected on one rail and through the differential are connected to the Neutral "output" from the apartment. So, according to some of you, the installation from the developer can cause problems?
If I missed something or misunderstood something, please correct me. May I ask for your comments, what do you think about the above summary? That is:
1) Can I connect three outlets to three phases and use one Neutral for all three outlets? This is the original question of this thread
2) Do you think the installation from the developer is "faulty" or could it be?

wilk2002 wrote:

Why, in your opinion, should I not pull 5x2.5mm and power three sockets from three phases, leading only one Neutral from them?

So that you don't ever power the devices connected to these sockets with phase-to-phase voltage. Why don't you listen to your elders if they're giving you good advice?

wilk2002 wrote:

that Neutral conductors from different phases are collected on one busbar

Exactly. All of them connect only on the bus. It's not like you're running one around the house.

retrofood wrote:

wilk2002 wrote:

Why, in your opinion, should I not pull 5x2.5mm and power three sockets from three phases, leading only one Neutral from them?

So that you don't ever power the devices connected to these sockets with phase-to-phase voltage. Why don't you listen to your elders if they're giving you good advice?

I listen as much as I can, I just want to understand and learn.
So if I run the same phase in all three cores, but use one N core, will it be ok? I don't have to push 3 phases, I can choose one (I just thought it would be better because I will spread the load over the phases).
It's really cramped in there... ... I would have to redo the entire switchboard just to have these three sockets on separate Neutrals, demolition for 2-3 days instead of a 2-3h job.

wilk2002 wrote:

but can you please give reasons for this recommendation?

Example.... You are planning one socket for the oven and the regulations are clear, each device above 2kW must have a separate circuit ... (CIRCUIT i.e. L+N+PE) and not a phase wire.
Another thing is the protection .... a 3P circuit breaker will be used, which will turn off everything when activated on one of the phases :?:

wilk2002 wrote:

I would have to redo the entire switchboard just to have these three sockets on separate Neutrals, demolition for 2-3 days instead of a 2-3h job.

And the dragons flew over the city.

wilk2002 wrote:

So if I run the same phase in all three cores, but use one N core, will it be ok?

It will not! With each phase conductor, you are to run separate N and PE conductors! And don't try to wipe your face with glass, because it's not fun.

Added after 52 [seconds]:

wilk2002 wrote:

... I would have to redo the whole switchgear

This is switchgear not a separation.

Added after 1 [minutes]:

wilk2002 wrote:

I would have to redo the entire switchboard just to have these three sockets on separate Neutrals, demolition for 2-3 days instead of a 2-3h job.

You have perform well And if you don't like it, why are you asking?

plum1978 wrote:

I do not support what you want to do, because it is certainly not a good solution, but on the other hand, demonizing a 3-phase RCD for 1-phase installations is funny to me.

Please note that your friend wants to run a 3-phase 1 (in words: one) N wire from this RCD and branch it along the route. And this is the problem you deign not to notice. Might be less fun.

plum1978 wrote:

I'm already blind from the monitor (next year I'll buy Eizo or Nec), but I'm not quite thinking. Of course, the idea of the author of the post is not the best / correct, but ask yourself if he / his wife will use these devices industrially like in the kitchen in the canteen, or maybe occasionally like each of us and whether, despite the asymmetric load, N will lead to the limit temperature destructive to insulation. In this case, I would be more worried about a good connection of 4 N wires, as well as damage to the RCD in the N track.

I am not worried about the temperature, but about the break in the N wire in a 3-phase installation. Besides, there is no trace of PE in the author's statements. And the RCD is supposed to be...
Are you serious now?

Once again, thank you very much for the discussion and all the comments. I particularly appreciate the practical approach to my problem. It is clear to me that according to the art, three separate circuits based on three 3x2.5mm wires should be made. However, I am asking you to evaluate the implementation of such an installation on one Neutral conductor so that I can save a lot of work and obtain a safe and functioning effect in home conditions for the above-mentioned receivers. In order to dispel doubts about my intentions, I allowed myself to put together a diagram of the planned connection. In my intentions, PE will not die, all three circuits will be secured with overcurrent, and the "bridging" of N'ki and PE will take place in the first box to which I would lead 5x2.5mm.
The "scheme" is located at https://prnt.sc/m1gfci
PS: Of course, there was a typo in the diagram, instead of RDC it should be RCD. It's getting late and that's why :/

wilk2002 wrote:

retrofood wrote:

wilk2002 wrote:

Why, in your opinion, should I not pull 5x2.5mm and power three sockets from three phases, leading only one Neutral from them?

So that you don't ever power the devices connected to these sockets with phase-to-phase voltage. Why don't you listen to your elders if they're giving you good advice?

I listen as much as I can, I just want to understand and learn.
So if I run the same phase in all three cores, but use one N core, will it be ok? I don't have to push 3 phases, I can choose one (I just thought it would be better because I will spread the load over the phases).
It's really cramped in there... ... I would have to redo the entire switchboard just to have these three sockets on separate Neutrals, demolition for 2-3 days instead of a 2-3h job.

What is the meaning of demolition 2-3 hours or 2-3 days if you do it for several dozen years?
Running a common neutral for 3 phase wires (different phases) causes the problems I wrote about and is impractical, because you will have to make additional junction boxes and make sure that the connections are secure.
If you lead a 5-wire cable from socket to socket to the next socket, connecting the wires to the terminals of the sockets, if the N cable loosens in one of the sockets, all appliances in the kitchen will burn.

But running a common neutral wire and 3 wires connected to the same phase is extreme stupidity and playing with fate.

You are probably surprised now - why?
You see, with current, if you have a common neutral for 3 circuits powered from 3 different phases, the current returning through the neutral will never be greater than the highest current of any of the phases. If you start to load subsequent phases, the current in the N conductor decreases.
For example, we have loads:

1 phase conductor L1 - 10A
2 phase wire L2 - 10A
3 phase wire L3 - 10A
N = 0A (zero)

No current flows through the neutral wire.

But let's now take an identical situation, but

1 phase conductor L1 - 10A
2 phase wire L1 - 10A
3 phase conductor L1 - 10A
N = 30A (sum of currents from all phase conductors)

Overcurrent protections are not only used to protect the installation in the event of short circuits, but also limit the value of the current flowing in the wires, i.e. they also protect the wires against overload/overheating.
Unfortunately, in such a situation as above, the neutral conductor may be overloaded and the contacts burnt, which in the case of standard sockets have a strength of 16A. This wire can burn up somewhere in the box or switchgear.

A few years ago I was asked to repair the installation in a detached house built by a developer. It turned out that the whole house almost burned down. The distribution box was covered with a wardrobe, and clothes hung in the wardrobe.
The electrician who performed the installation there did it exactly as you want it to be done, i.e. the entire installation was divided into lighting and socket circuits.
It's just that several phase wires, each with a separate 20A protection, and one neutral wire were led to both the lighting and the sockets. Unfortunately, the house was powered by 1-phase, because it was cheaper. The developer was "riding" maximally at cost.
As a result, the terminal block of the neutral conductor in the distribution box burned up. Puffs of smoke appeared. Thanks to the fact that it happened during the presence of the household members, they managed to throw all the clothes out of the wardrobe and disconnect the power supply in time before the fire broke out. But the wall remained sooty. There was a burning smell throughout the house.
When I saw it, my hair stood on end. I called the electrician who did the installation. He explained that the developer told him to do so. Unfortunately, he built several houses there, and in each of them the same problem.
I probably have pictures of that box somewhere. If I find it, I'll throw it.

mawerix123 wrote:

Example.... You are planning one socket for the oven and the regulations are clear, each device above 2kW must have a separate circuit ... (CIRCUIT i.e. L+N+PE) and not a phase wire.

wilk2002 wrote:

but can you please give reasons for this recommendation?

This is a "pure" operational recommendation.
As in the circuit with a receiver above 2kW, you will turn on the additional ones
receivers, it may inadvertently turn off the fuse - accidental overload. Just enough.
There is no prohibition of connecting to any socket on a multi-socket circuit a receiver with a power of more than 2kW.

wilk2002 wrote:

However, I am asking you to evaluate the implementation of such an installation on one Neutral conductor so that I can save a lot of work and obtain a safe and functioning effect in home conditions for the above-mentioned receivers.

If these are single-phase circuits, this cannot be done, because the N conductor must have the same cross-section as the N conductor.
The 3+N circuit is a 3-phase WLZ.
Dangerous situation. If the N comes loose in the box, you will damage the receivers.
WLZ can be done, but it requires experience and the use of good quality elements.
This poses a risk of failure also in the switchgear.
In general, the N wires can be disconnected with impunity - this N from the WLZ just not.

Thank you very much for all the answers. I didn't write back because of the New Year's Eve period
I will take all your comments to heart.

I have another question regarding the following:

Plumpi wrote:

Such a system will work, and theoretically the current flowing through the neutral conductor should never be greater than the highest current flowing in any of the phases.

Plumpi wrote:

For example, we have loads:

1 phase conductor L1 - 10A
2 phase wire L2 - 10A
3 phase wire L3 - 10A
N = 0A (zero)

No current flows through the neutral wire.

This is probably elementary knowledge, but unfortunately I do not understand the above. It is logical for me to add up N'ki's load when I use one phase, but I don't know why the load will "cancel" when three different phases are fully loaded. What should I read to understand this? What should I look for to find out why this is happening? What do I need to learn to be able to calculate it myself or at least understand it?

wilk2002 wrote:

This is probably elementary knowledge, but unfortunately I do not understand the above. It is logical for me to add up N'ki's load when I use one phase, but I don't know why the load will "cancel" when three different phases are fully loaded. What should I read to understand this? What should I look for to find out why this is happening? What do I need to learn to be able to calculate it myself or at least understand it?

Because the three-phase network consists of three phases with sinusoidal waveforms, the voltages of which are shifted relative to each other by 120°
This is what the graph of these waveforms looks like:
https://www.wykop.pl/cdn/c3201142/comment_gfIDFnITNVbs7El3wtCrP6xUubtsnn8D.jpg

If we take any time point on this graph and add up the voltages of all the phases, it will always be 0 (zero).
Below the central axis, the graphs have a negative sign and above the positive sign.
The same happens with currents if all phases are loaded with receivers of the same power.

wilk2002 wrote:

What do I need to learn

You don't have to learn anything, just do what you can and leave the electrics to the electricians.

You too Plumpi.