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Distributor's Box Wiring: Bridging PE with N or Creating Additional Grounding?

Piotrekh75 36429 41
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How should I wire a construction switchboard when the supply has 3 phases and neutral but no separate ground: bridge PE to N, add grounding, or rely on an RCD?

If the supply is TN-C with a PEN conductor, bring the PEN to the construction switchboard and split it into separate N and PE there; do not make an arbitrary PE–N bridge in the wrong place [#15910873][#15911018][#15911027] The PEN must have the correct cross-section: at least 10 mm² Cu or 16 mm² Al [#15910873][#15911027] Install a 3-phase RCD, and for a construction board add temporary protective earthing if needed, but do not rely on a fixed 10 Ω rule—replies point instead to the applicable construction-site rules/standard (7-704) [#15911027][#15912132][#15911805] The exact solution depends on the connection conditions and the network system (TN or TT), so those documents must be checked before wiring [#15909978][#15910172][#15910671][#15910692] Because this is a construction switchboard, the protection should be verified by an electrician with measurements [#15910184][#15910671]
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  • #1 15909965
    Piotrekh75
    Level 8  
    Hello

    I have a layout according to the drawn diagram. The distributor gives 3 phase and neutral. No ground line. Please let me know if I should bridge PE with N in the distributor's box, or maybe in the construction one. Should I make additional grounding in the ground, or maybe a differential will suffice.

    Please give me specifics. Distributor's Box Wiring: Bridging PE with N or Creating Additional Grounding?
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  • #2 15909970
    kkas12
    Level 43  
    The distributor is rather fuel "gives".
  • #3 15909978
    Łukasz-O
    Admin of electroenergetics  
    Details are in the Terms of Connection. It shows how the network works.
    RCD is missing in the picture. Where to get PE? Are you asking as an investor or contractor?
  • #4 15909981
    zbich70
    Level 43  
    What is in connection conditions - network system?

    (Luke warned)
  • #5 15910020
    zubel
    Conditionally unlocked  
    You have everything written in the power conditions. If an earth ground is required it will probably be 10 ohms and you will need to make it yourself.
  • #6 15910026
    Łukasz-O
    Admin of electroenergetics  
    zubel wrote:
    (...) If an earth electrode is required it will probably be 10 ohms and you have to do it yourself.

    And where does this magical value come from? Can my friend clear this up?
  • #7 15910113
    retrofood
    VIP Meritorious for electroda.pl  
    Piotrekh75 wrote:
    The distributor gives 3 phase and neutral. No ground line.


    Who is he giving it to and why would he do it?
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  • #8 15910155
    Piotrekh75
    Level 8  
    I would like everyone to understand me well. The description of the box in the house is how to perform grounding. The box I am asking about is a construction box standing in the middle of nowhere. So I will not connect the grounding since there is no foundation and reinforcement yet. I am asking as an investor, I am building an economic system.
  • #9 15910172
    jdubowski
    Tube devices specialist  
    Piotrekh75 wrote:
    I would like everyone to understand me well.


    That's right - "everyone" has already asked for a description of the network layout of the connection conditions N times. Then everyone will understand you.

    Piotrekh75 wrote:
    The box I am asking about is a construction box standing in the middle of nowhere. So I will not connect the grounding since there is no foundation and reinforcement yet.


    In addition to the foundation earth electrode, science and practice know several other types of earth electrode. This grounding can be treated as temporary.
  • #10 15910174
    elpapiotr
    Electrician specialist  
    Author, when you answer questions previously asked by colleagues, you will receive specific answers. Otherwise none of it.
  • #12 15910183
    zbich70
    Level 43  
    Piotrekh75 wrote:
    I'm building an economic system.

    There is no concept of "economic system" in the electrical industry.
    Electrical installations may only be carried out by suitably qualified persons. Dot.
    In the case of construction switchboards, even more so.

    But if you must play Zosia-Samosia (meaning "economic system"), then be kind enough to answer posts #3 and #4.
    The keyword is network system, TN or TT?
    It is very important for an electrician, but these letters probably don't mean anything to a colleague ...
  • #13 15910184
    CYRUS2
    Level 43  
    Piotrekh75 wrote:
    I would like everyone to understand me well.
    It's you "you don't get anything" Colleagues on the forum understood everything well.
    Terms of connection - it's all written there.
    Piotrekh75 wrote:
    So I will not connect the grounding since there is no foundation and reinforcement yet. I am asking as an investor, I am building an economic system.
    You are not for connecting - especially the switchgear. Hire an electrician.
    If it is as you write, the earth electrode will not provide you with electric shock protection. Even if it's 10 ohms.
    You need to hire an electrician to make a suitable switchgear.
    And to measure the effectiveness of protection.
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  • #14 15910231
    anarkh
    Level 13  
    In addition, the earthings present in cable connectors are working earthings, not protective earthings. Most LV distribution networks operate in the TN-C system, so it is important that the investor performs protective earthing on his own.
  • #15 15910585
    Piotrekh75
    Level 8  
    I have the installation in the building TN-S, I do not have a project for the construction box.
  • #16 15910671
    elvis13
    Level 18  
    Piotrekh75 wrote:
    I have the installation in the building TN-S, I do not have a project for the construction box.

    What do we care about this building? You write that...

    You have a building connection to a plot with nothing on it.
    There you have those construction switchboards.

    In order for you to connect, you had to apply for Connection Conditions.
    You must have had an answer to that request. This is the document we're talking about.

    Find it and read it. Look for information about the network layout. TT or TN.
    It's best to post a scan.

    Here you have an example WP http://bedzin.bip.info.pl/plik.php?id=17964 Information for this particular document is on page 3.

    You cannot be considered to have protection against electric shock until confirmed by measurements.
    It will be more economical to hire an electrician with measuring equipment than to buy a meter yourself that you need to be able to handle and understand the results.
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  • #17 15910680
    Piotrekh75
    Level 8  
    Maybe the photo I took will help. If I understood correctly, the terminal on my box is PEN, so that would solve the problem? Distributor's Box Wiring: Bridging PE with N or Creating Additional Grounding?
  • #18 15910692
    elvis13
    Level 18  
    Whether it is a PEN or N connector will be written in the Connection Conditions. The photos of this box do not show what Tauron has between the transformer and this box!

    The diagram in the box may be wrong! The manufacturer of the boxes does not know what the network layout is. This is known by the distribution network operator.

    Boy, have mercy and find this document! Don't go without it!


    By the way, someone could reprimand the producers because they actually give PEN everywhere...
  • #19 15910720
    mawerix123
    Level 39  
    In response to a sentence in red print. You can't connect two N and PE wires to this zug, it's not even about the PEN chapter, but about the connection itself.

    elvis13 wrote:
    Boy, have mercy and find this document!


    And Electrician!
  • #20 15910734
    Piotrekh75
    Level 8  
    Ok, I know what it is, I'm sending the data
    Attachments:
    • Warunki008.pdf (1.5 MB) You must be logged in to download this attachment.
  • #21 15910871
    Karamba2014
    Level 9  
    1- whether this (construction) box will stand in one place throughout the construction
    2-in the box there should be a 3-phase differential
  • #22 15910873
    elvis13
    Level 18  
    Fixed. You have a TN-C network layout.

    You have a PEN, which is a wire with two functions:
    1. PE protective conductor functions
    2.Neutral wire functions
    as long as he is min. 10mm2 for Cu, 16mm2 for Al.

    What are you going to do next?
  • #23 15910884
    CYRUS2
    Level 43  
    anarkh wrote:
    In addition, the earthings present in cable connectors are working earthings, not protective earthings.
    Where did you learn - from your grandfather with knowledge at the level of Comrade Gomułka?
    elvis13 wrote:
    By the way, someone could reprimand the producers because they actually give PEN everywhere...
    By the way, you don't know what you're talking about.
    PEN is not a gadget bought in a supermarket.
  • #24 15910998
    Piotrekh75
    Level 8  
    elvis13 wrote:
    Fixed. You have a TN-C network layout.

    You have a PEN, which is a wire with two functions:
    1. PE protective conductor functions
    2.Neutral wire functions
    as long as he is min. 10mm2 for Cu, 16mm2 for Al.

    What are you going to do next?


    I have Erbetka L232, I intend to connect it by plugging it into the N + PE meter box under one terminal.

    Karamba2014 wrote:

    1- whether this (construction) box will stand in one place throughout the construction
    2-in the box there should be a 3-phase differential


    The box will stay in one place, there is no differential in the erbetka, but I can buy it.
  • #25 15911018
    Karamba2014
    Level 9  
    You can connect the meter box to the erbetka with one PEN cable and in the erbetka break into separate N and PE
  • #26 15911027
    kkas12
    Level 43  
    You can, but this PEN should have the right cross-section. 10mm2 for Cu or 16mm2 for Al.
    And you're not doing any favors with the RCD. You need to mount it.
    PE grounding is also recommended, unless your box will be standing next to the connection and measurement post.
  • #27 15911035
    Karamba2014
    Level 9  
    You can always stick pins into the ground and if the measurements are good, ground it from it
  • #28 15911093
    kkas12
    Level 43  
    When will they be good and when will they be bad?
  • #30 15911274
    kkas12
    Level 43  
    Where did your friend read that?
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Topic summary

✨ The discussion revolves around the proper grounding methods for a construction distributor's box that provides three-phase power and neutral but lacks a dedicated ground line. Participants emphasize the importance of adhering to connection conditions and the necessity of protective earthing (PE) to ensure safety. The use of a PEN conductor, which serves dual functions as a protective earth and neutral, is debated, with recommendations for proper cross-section sizes (10mm² for copper, 16mm² for aluminum). The need for a residual current device (RCD) is highlighted, and the significance of measuring grounding resistance is discussed, with a target of below 10 ohms for effective protection. The conversation also touches on the implications of different network systems (TN-C, TN-S) and the importance of hiring qualified electricians for installation and measurement tasks.
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FAQ

TL;DR: In Polish LV grids, ≤0.4 s disconnection is required for circuits ≤32 A (IEC 60364); “PEN is a wire with two functions” [Elektroda, elvis13, post #15910873] Keep PEN intact, split to PE + N in the switchboard, add a 30 mA RCD.

Why it matters: Correct PEN handling prevents lethal touch voltages during construction.

Quick Facts

• Supply type in most rural plots: TN-C with combined PEN conductor [Elektroda, elvis13, post #15910873] • Minimum PEN size: 10 mm² Cu / 16 mm² Al (PN-HD 60364-5-54) [PN-HD 60364] • Mandatory disconnection time: ≤0.4 s for ≤32 A circuits (IEC 60364-4-41) [IEC, 2020] • Recommended RCD for site boards: 4-pole, IΔn = 30 mA, typ. cost €50–80 [Hager, 2023] • Earth electrode: used mainly as PEN backup; no fixed ≤10 Ω rule in TN-C [Elektroda, kkas12, post #15911825]

What network system is usually delivered when the utility gives 3 phases plus neutral?

The connection is almost always TN-C, meaning the neutral and protective functions share one PEN conductor up to your board [Elektroda, elvis13, post #15910873]

Should I bridge PE with N in a construction switchboard?

Yes. In TN-C you must split the incoming PEN into separate PE and N bars and link them with a removable PEN link or terminal; this equals “bridging” inside the board, not in downstream sockets [Elektroda, Karamba2014, post #15911018]

Where exactly do I separate PEN into PE and N?

Do it at the first switchboard you own (the site box). Use a dedicated PEN terminal, then feed PE and N to downstream RCDs and circuits [Elektroda, kkas12, post #15911027]

What cross-section must the PEN conductor have?

Regulations require minimum 10 mm² copper or 16 mm² aluminium for any PEN in TN-C systems [PN-HD 60364-5-54].

Do I need a separate earth electrode for the temporary board?

It is recommended but not obligatory for shock protection in TN-C; its main role is to stabilise voltage if the PEN fails [Elektroda, kkas12, post #15912132]

Is there a target resistance value for that electrode?

Standards give no single number; the loop impedance must still let protective devices trip within 0.4 s. Values below 30 Ω help, yet protection is verified by loop-impedance measurement, not earth-resistance alone [Elektroda, kkas12, post #15911274]

Is a 30 mA RCD compulsory on construction sites?

Yes. IEC 60364-7-704 and Polish rules demand 30 mA RCDs on all socket circuits at sites. A 30 mA unit trips in 30–40 ms under test conditions [Hager, 2021].

How do I confirm protection is effective?

An electrician measures fault-loop impedance Zs and RCD trip time. Zs × 230 V must stay below protective-device disconnection voltage (≤0.4 s for breakers ≤32 A) [IEC, 2020].

What happens if the PEN conductor breaks?

All exposed metal bonded to PE can rise to full phase voltage, creating a fatal touch hazard; any auxiliary earth only slightly reduces this risk [Elektroda, MARCIN.SLASK, post #15911857]

How do I link a TN-C supply to my future TN-S house system?

  1. Feed PEN from utility to site board.
  2. Split PEN to PE + N using a certified link.
  3. Run five-core cable (L1-L2-L3-N-PE) from the board into the building installation. [Elektroda, Karamba2014, post #15911018]

May I use a temporary rod earth before foundations are poured?

Yes; drive 2–3 steel rods ≥1.5 m into moist soil and bond to the PE bar. Treat it as provisional and retest after permanent foundation earth is installed [Elektroda, jdubowski, post #15910172]

Edge case: What if loop impedance is high even with PEN intact?

Install an RCD and shorten cable runs; if Zs still exceeds the limit, use a dedicated transformer or lower-rated breaker to satisfy the 0.4 s rule [IEC, 2020].

How much does a compliant site board upgrade cost?

Adding a 4-pole 40 A/30 mA RCD, PEN link, and test terminals typically costs €100–150 in parts plus labour [Hager, 2023].
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