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Connecting RB Switchgear for Construction: TN-C System, PEN to PE/N Separation, 15kV Experience

ADI-mistrzu 11259 12
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  • #1 16649228
    ADI-mistrzu
    Level 30  
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    Hello,

    I need to connect the RB switchgear for construction purposes.

    When it comes to electrical qualifications, of course I have them (up to 15kV), but I have never worked with this type of installations so I would like to make sure that what I do is correct.

    I attach the connection conditions below:
    Connecting RB Switchgear for Construction: TN-C System, PEN to PE/N Separation, 15kV Experience
    As you can see, the network is in the TN-C system, and the contents of the ZK box look like this:
    Connecting RB Switchgear for Construction: TN-C System, PEN to PE/N Separation, 15kV Experience
    On the right there is a countdown protection, and in the box on the left, if I understand correctly, I have to lead with this blue conduit my cable from the RB switchgear and plug in the terminals.

    In the RB switchgear, of course, 3-phase differential protection and overcurrent protection. In addition, the division of PEN into PE and N through a driven spike into the ground.
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  • #2 16649242
    mawerix123
    Level 39  
    Posts: 4143
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    What cable do you supply to this RB :?:
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  • #3 16649410
    ADI-mistrzu
    Level 30  
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    I don't have a cable yet, I'm going to RB move about 5m from ZT. I have read that the cable should be 10mm? for continuous loads, but does it make sense to RB? In the construction of foundations, there will be practically no electricity used, glue is foreseen for masonry, so as much as a mixer or brick saw, the rest is the treatment of rafters, etc. Concrete imported in concrete mixers.
    That's why I'm thinking about the 4mm? line.
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    #4 16649469
    zbich70
    Level 43  
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    ADI-mistrzu wrote:
    I don't have a cable yet, I'm going to RB move about 5m from ZT. I have read that the cable should be 10mm? for continuous loads, but does it make sense to RB? (...).

    You run the power supply from ZK to RB in such a system as the power supply network, i.e. TN-C.
    This determines the minimum PEN cross-section - 10mm? Cu or 16mm? Al.
    If the cable, then of course in pressed sleeves.
    It is hard to deduce from the photo, but the strip supports 25mm?. But this must be checked.
    ADI-mistrzu wrote:
    That's why I'm thinking about the 4mm? line

    You cannot use this cross-section in the TN-C system.
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    #5 16649526
    mawerix123
    Level 39  
    Posts: 4143
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    ADI-mistrzu wrote:
    In the construction of foundations, there will be practically no electricity used, glue is foreseen for masonry, so as much as a mixer or brick saw, the rest is the treatment of rafters, etc. Concrete imported in concrete mixers.


    Looking at this from a load point, you probably don't need such a large cross-section as 10mm2 Cu to power your home, so why overpay? ;)

    ADI-mistrzu wrote:
    That's why I'm thinking about the 4mm? line


    The rope is not even, you already know that 4mm2 falls off in TN-C and besides, if the price does not come out as you will give such a cable as it should :?:
  • #6 16649652
    ADI-mistrzu
    Level 30  
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    Yes, the ends of the wires will be pressed, I just need to borrow a crimper because mine supports up to 6mm, come now I wonder if I would give a normal solid wire, I will not have to run after my friends during the holiday season ...
    So to sum up, I lead a 4x10mm? (copper) wire to RB, I split the PEN into N and PE and I connect the splitting point to an additional grounding spigot that I will probably stick right next to RB'tki.
  • #7 16650733
    polaklbn
    Level 24  
    Posts: 594
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    And after equipping TL, I can't tell if the network is TNC or TT.
    I recommend you buy a cable like in the building design. At the next stage, you will only unplug the RB and insert the cable into the switchboard.
    And try not to write about the cable, because you can't lay the cable in the ground.
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  • #8 16650969
    ADI-mistrzu
    Level 30  
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    @polaklbn , I understand as a wire a single wire, part of a cable. Like in foreign literature, "wire" is a single wire in "cable".
    As for the final cable that will be under the building, in my opinion a bit hard, I have the building on the foundation slab. In this case, I have to move RB away from the workplace anyway until they finish work, and then dig the wire.

    Most likely it will be that I lead a second cable to the building, I will need a total of 15m, the building is moved away from the fence 10m and the target switchgear will be in the garage, so I don't know if for a few zlotys (compared to other costs) it makes sense actually save on this cable.

    By the way, I bought a 10mm? wire once.
  • #9 16651042
    mawerix123
    Level 39  
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    polaklbn wrote:
    And after equipping TL, I can't tell if the network is TNC or TT.


    After all, it is determined by the connection conditions.

    ADI-mistrzu wrote:
    I understand as a wire a single wire, part of a cable.


    Meanwhile....

    ADI-mistrzu wrote:
    I lead a 4x10mm? cable

    ADI-mistrzu wrote:
    and then dig the wire

    ADI-mistrzu wrote:
    I will lead a second cable to the building


    It's a cable to be a cable, how many fronts it must have :?: because four is not a cable yet.

    ADI-mistrzu wrote:
    By the way, I bought a 10mm? wire once.


    How to understand :?:
  • #10 16651137
    polaklbn
    Level 24  
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    Buddy, there are wires, cables and wires. You can't bury the cord in the ground anymore.
    If you bought YKY 4x10mm then you bought a cable.
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  • #11 16657708
    ADI-mistrzu
    Level 30  
    Posts: 2261
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    Geez ... I caught this cable myself ...
    Yes, a YKY 4x10mm ^ 2 cable is already installed, in total RB is 5m away from the meter box.

    I still have a question for you, I have to fill out the contractor's statement which is very confused at PGE.
    The statement includes:
    "Reports on measurements of insulation resistance, effectiveness of electric shock protection
    and the efficiency of lightning protection with positive results and the wiring diagram *
    I left the recipient. I used additional protection against electric shocks in the electrical installation
    made through ............................................................... "
    Where * means delete as appropriate.

    The letter is probably general for installation in a finished building as well as in a construction switchboard.
    Insofar as it is logical to take measurements of insulation resistance and electric shock protection, lightning protection and diagram are not likely to apply to RB anymore?
    I tried to find a recipe specifying what to do, but for the most part it is ZE.
    The conditions indicate that the installation should be carried out safely and by a person with electrical qualifications.
  • #12 16657867
    elpapiotr
    Electrician specialist  
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    Hello.
    Not quite with this logic, mate.
    * Delete where not applicable is very adequate to the situation, because you cannot measure the effectiveness of electric shock protection without having the voltage specified for the installation.
    You wrote about the "lightning" installation yourself, but the diagram applies :D
  • #13 16658089
    ADI-mistrzu
    Level 30  
    Posts: 2261
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    The further into the forest the darker ...

    Below is what the writing looks like:
    Connecting RB Switchgear for Construction: TN-C System, PEN to PE/N Separation, 15kV Experience
    So it remains only to measure the insulation and its scheme, come on, I can sketch it later if necessary, because there is an annotation that they were left with the recipient, i.e. with me.

    It is more interesting with the "Affiliated entity statement", namely:
    " ... were taken back by a person authorized to
    performing independent functions in construction to the required extent, and acceptance has been
    confirmed by acceptance protocol without reservations (positive acceptance protocol)     "
    I can forgive myself the acceptance protocol, but are you suddenly not required any building permits? I understand the building installation, but for temporary installation?
    Theoretically, construction has not yet begun, there is no statement yet to be made about it, so by law it is rather just a piece of land.

    The above is already asking more out of curiosity for the future because I will try to submit a letter with only electrical permissions.
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Topic summary

✨ The discussion revolves around connecting RB switchgear for construction within a TN-C electrical system. The user, experienced up to 15kV, seeks guidance on proper installation practices, particularly regarding the separation of PEN into PE and N, and the appropriate cable specifications. Responses highlight the necessity of using a minimum PEN cross-section of 10mm² for copper or 16mm² for aluminum, with suggestions to use a 4x10mm² YKY cable for the connection. The conversation also touches on the importance of insulation resistance measurements and the requirements for electrical shock protection, as well as the need for compliance with local regulations regarding temporary installations. The user expresses concerns about the documentation required for the contractor's statement and the implications of building permits for temporary setups.
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FAQ

TL;DR: For TN-C temporary construction power, run a 4‑core feed and keep PEN ≥ 10 mm² Cu; “You cannot use this cross-section in the TN-C system.” [Elektroda, zbich70, post #16649469] Why it matters: Picking the wrong conductor size or grounding method can void approvals and create shock risk. This FAQ helps site electricians connect RB switchgear safely under TN‑C with PEN→PE/N separation.

Quick Facts

How do I power an RB switchgear from a TN-C service?

Run the supply from the ZK/ZT in the same TN‑C system. Use a conductor with a PEN at least 10 mm² Cu (or 16 mm² Al). Terminate with pressed sleeves if it is a cable. Keep the PEN intact up to the RB. This matches the supply topology and meets the minimum PEN size quoted in the thread. “You run the power supply from ZK to RB in such a system as the power supply network.” [Elektroda, zbich70, post #16649469]

Can I use 4 mm² to feed the RB if the load is small?

No. In TN‑C, you cannot use 4 mm² for the PEN. The thread states the minimum PEN cross‑section is 10 mm² Cu or 16 mm² Al, regardless of low expected load. Choose sizing that respects the PEN requirement rather than the tool duty. “You cannot use this cross-section in the TN-C system.” [Elektroda, zbich70, post #16649469]

Where do I split PEN into PE and N for a temporary construction setup?

Split PEN into PE and N inside the RB. Bond the PEN‑splitting bar to a local earth electrode installed near the RB. This creates the PE/N separation point for downstream TN‑S style distribution from the RB. Keep the upstream as TN‑C from the ZK/ZT to RB. [Elektroda, ADI-mistrzu, post #16649652]

Is YKY 4×10 mm² an acceptable cable to the RB?

Yes. The thread author confirmed installing YKY 4×10 mm² Cu from the meter box to the RB (about 5 m). This aligns with the 10 mm² PEN requirement when run as TN‑C to the RB. Ensure proper terminations with crimped lugs/sleeves. [Elektroda, ADI-mistrzu, post #16657708]

Cable vs. wire vs. cord—what can go underground?

Use cable underground; do not bury cords. The thread clarifies that cords are not suitable for burial, while a cable like YKY is. Select products rated for direct burial and follow depth and protection practices. “If you bought YKY 4x10mm then you bought a cable.” [Elektroda, polaklbn, post #16651137]

Do I need RCDs and overcurrent protection in the RB?

Yes. The RB should include three‑phase residual‑current protection and overcurrent protection. This protects portable construction tools and sub‑circuits from shock and overloads. Fit devices per your load plan and labeling. [Elektroda, ADI-mistrzu, post #16649228]

TN-C or TT—how do I tell from the connection conditions?

Rely on the connection conditions issued by the utility. In the thread, responders emphasize that the conditions determine TN‑C vs TT. If documents say TN‑C, wire the feed accordingly to the RB. “It is determined by the connection conditions.” [Elektroda, mawerix123, post #16651042]

What measurements go on the contractor’s declaration for a temporary RB?

Provide insulation resistance measurements and, where applicable, shock protection effectiveness. The thread notes you cannot measure shock protection effectiveness without the specified supply voltage. Include a wiring diagram, deleting sections that do not apply. [Elektroda, elpapiotr, post #16657867]

Edge case: What if supply voltage isn’t available yet for testing?

You cannot verify shock protection effectiveness without the installation’s specified voltage present. In such a case, document insulation resistance and include the diagram, then complete remaining tests after energization. “Delete where not applicable” was highlighted for forms. [Elektroda, elpapiotr, post #16657867]

Do I need a building acceptance protocol for a temporary RB before construction starts?

The thread’s author questioned a form asking for acceptance by a person authorized for construction functions. They planned to submit with electrical permissions only, noting the site is just land pre‑build. Check your utility’s exact form and strike non‑applicable parts. [Elektroda, ADI-mistrzu, post #16658089]

What tools do I need for proper terminations at the RB and ZK?

Use a crimping tool sized for ≥10 mm² lugs or sleeves. The author noted their crimper only supported up to 6 mm² and planned to borrow a larger tool. Correct crimping ensures reliable PEN continuity and thermal performance. [Elektroda, ADI-mistrzu, post #16649652]

How far can I place the RB from the meter box?

In the thread, the RB sat about 5 m from the meter box. Another run of about 15 m was considered for the future main board. Keep runs short for voltage drop and practical protection selectivity. [Elektroda, ADI-mistrzu, post #16650969]

Quick how-to: PEN split and earthing at the RB?

  1. Bring TN‑C feed (with ≥10 mm² Cu PEN) into RB.
  2. Split PEN into PE and N on the main earthing terminal inside RB.
  3. Bond the split point to a local earth electrode installed near the RB. [Elektroda, ADI-mistrzu, post #16649652]

Can I size the feeder only by expected tool load (e.g., mixer, saw)?

No. Even with light, intermittent loads, the PEN minimum rules the sizing in TN‑C. The thread rejects 4 mm² due to PEN requirements, not load estimates. Follow the structural minimum first; then check voltage drop and thermal limits. [Elektroda, zbich70, post #16649469]

What does RB switchgear include in a typical construction setup?

It is a temporary distribution board with incoming TN‑C feed, PEN split to PE/N, RCDs, and overcurrent devices. Outgoing circuits serve site tools and later can be reconfigured for the permanent board. Label circuits clearly for handover. [Elektroda, ADI-mistrzu, post #16649228]

What if my project documents specify a different cable than I planned?

Buy the cable specified in the building design. One responder suggested using the designed cable so you later disconnect the RB and feed the permanent switchboard without rework or waste. [Elektroda, polaklbn, post #16650733]
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