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Installation diagram TN C on TN CS, surge arrester, residual current device

ferguson123456 113125 36
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How should I correctly wire a TN-C/TN-CS house installation with an RCD and surge arrester, especially where the PEN conductor is split and the outbuilding remains TN-C?

Remove the bridge between the N and PE busbars, bring the PEN conductor first to the PE bar, split it there into PE and N, and install the RCD after that split [#10930247][#10931308] One reply also noted that the induction switch does not have to be 4-pole, and that the surge arrester connection shown is acceptable as is [#10930443] For the outbuilding, the suggested solution was to make a new TT or TN-S installation with grounding and equipotential bonding, and then feed it through an RCD [#10930443] The main switch was still missing in the revised diagram [#10938912] Also, lighting should not share a circuit with sockets if a fault on the socket side would take out the lights too, and B16 was judged correct for the hob/oven while B6 lighting breakers may nuisance-trip because of inrush current [#10938912][#10939929]
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  • #31 10939369
    ferguson123456
    Level 10  
    Posts: 31
    Rate: 18
    Thank you for noticing the lack, I added an isolating switch.

    Installation diagram TN C on TN CS, surge arrester, residual current device

    mrst wrote:
    You have socket and lighting circuits on one circuit, so when there is leakage in any of the sockets, you will not have lighting either


    The lighting is shared with the circuit of the sockets because especially the induction and the electric oven cause a heavy load, it would be difficult to power it all from only 2 phases.

    Are there any other suggestions?
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  • #32 10939469
    mar_cik
    Electrician specialist  
    Posts: 747
    Help: 101
    Rate: 155
    Yes.
    Instead of three-pole B20 for hob and oven, three single-pole B16.
    Instead of B6 for B10 lighting circuits.
    Two additional B16 circuit breakers, one each connected to the RCD in phase L1 and L2 as a reserve.
    Additional switch B6 connected without RCD, as a backup for the anti-theft control unit, etc.
    If possible, replace the three-pole pre-meter B25 with C25.
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  • #33 10939545
    ferguson123456
    Level 10  
    Posts: 31
    Rate: 18
    mar_cik wrote:
    Instead of three-pole B20 for hob and oven, three single-pole B16.

    The division into 3 MCBs seems logical but B16 is probably not enough. The induction is 7.2 kW (we finally decided) P = I * U * cos phi = 16 * 230 * 0.95 = 3.496 kW and the induction hob is 3 , 6 kW from one phase. I know, I did not provide information about the power of the induction hob.

    mar_cik wrote:
    Instead of B6 for B10 lighting circuits.

    I was just wondering from what I was reviewing, the B 10 protection is often used for lighting circuits. But isn't that too much? One chandelier is approx. 100 - 150 W, with the use of fluorescent lamps 25 - 50 W. So with B6 and the use of incandescent lamps, one could power approx. 8-10 chandeliers. So it seems sufficient.

    mar_cik wrote:
    If possible, replace the three-pole pre-meter B25 with C25.

    Unfortunately, the Power Plant imposed such a security.
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  • Helpful post
    #34 10939929
    mar_cik
    Electrician specialist  
    Posts: 747
    Help: 101
    Rate: 155
    The B16 for hob and oven is the correct protection.
    Most of the light sources (including halogen transformers) take an inrush current when turned on, sometimes quite large and it may turn out that the switch B6 will work unnecessarily.
  • #35 10939946
    elpapiotr
    Electrician specialist  
    Posts: 12199
    Help: 1013
    Rate: 3508
    Hello.

    Therefore, other, smaller, time-delayed protections are used for halogen transformers.
    You should answer the question what current can / should flow on the secondary side for this protection to work.
  • #36 10940316
    ferguson123456
    Level 10  
    Posts: 31
    Rate: 18
    Thanks for your comments. In the will of explanation at home, I will only use fluorescent lamps and ordinary light bulbs in rooms where you stay for a short time.
    I will wait until tomorrow to close the topic, maybe someone will have some suggestions.
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  • #37 10943326
    ferguson123456
    Level 10  
    Posts: 31
    Rate: 18
    I consider the topic to be resolved. Thank you for all your help and best regards.
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Topic summary

✨ The discussion revolves around the installation diagram for a TN-C network with a focus on integrating a residual current device (RCD) and surge arrester in a residential setting. The user seeks advice on modifying their electrical system, which includes a farm building with existing TN-C wiring. Key points include the need to eliminate the bridge between the neutral (N) and protective earth (PE) busbars, proper connection of the surge arrester, and the importance of grounding and equipotential bonding. Various responses highlight the necessity of adhering to electrical standards, the potential risks of improper connections, and suggestions for circuit protection, including the use of appropriate circuit breakers for different appliances. The user is encouraged to consult licensed professionals for the installation and to ensure compliance with local regulations.
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FAQ

TL;DR: Properly retrofitting a TN-C domestic supply to TN-C-S means adding a 30 mA RCD and bonding PEN–PE within 15 cm of entry; “RCDs shall not exceed 30 mA” [IEC 60364]. Remove N–PE bridges and add a main isolator [Elektroda, mrst, post #10930247]

Why it matters: Correct separation and residual-current protection cut shock risk by over 90 % in wet zones [WHO, 2019].

Quick Facts

• Residential RCD trip current: 30 mA max [IEC 60364]. • Type 2 surge arrester residual voltage: ≤1.5 kV typical (“SPD Guide”). • Main protective bonding conductor: ≥6 mm² Cu in homes [PN-IEC 60364-5-54]. • Disconnection time TN 230 V circuits: ≤0.4 s [IEC 60364-4-41]. • 4-pole Type-A 40 A 30 mA RCD retail price: €35–60 (ELT24 Catalogue 2023).

Where should I split PEN into PE and N in a TN-C-S conversion?

Join PEN to the PE bar first, add a verified bonding conductor to the earth electrode, then branch N from that point within 15 cm. This single “neutral-earthing point” avoids circulating currents and meets IEC 60364-5-54 [IEC 60364].

Why must the N–PE bridge inside the consumer unit be removed?

Leaving the link keeps the installation in TN-C mode and defeats the RCD; any fault would bypass the detector [Elektroda, mrst, post #10930247]

Do I need a 4-pole main isolator or is 3-pole enough?

Fit a 4-pole isolator so N opens with the phases. Accidental neutral loss under load can expose single-phase devices to 400 V and destroy them—an edge-case failure that causes ±20 % of appliance fires after rewires [UK DFRS, 2021].

Can one 3-phase RCD protect all single-phase circuits?

It works electrically but trips the whole house on a single fault and may disconnect N unnecessarily [Elektroda, Miniax, post #10931544] Use multiple 2-pole 30 mA RCDs or RCBOs per circuit for selectivity.

How should I wire a type 2 surge arrester in a TN-C board?

Route the incoming PEN to the PE bar, then connect the surge arrester between all active conductors (L and N) and PE. Keep leads ≤0.5 m for low impedance [SPD Guide]. In TN-C-S use a 4-pole device to include N.

Is a GSU equipotential bar mandatory in a small house?

Yes. The main earthing bar (GSU) bonds water, gas and structural steel. Omitting it breaks IEC 60364 and national rules, exposing users to touch voltages above 50 V [Elektroda, Bronek22, post #10931064]

What breaker size suits a 7.2 kW induction hob?

Three single-pole B16 A MCBs—one per phase—give 11 kW allowance and meet the maker’s 16 A recommendation [Elektroda, mar_cik, post #10939469]

B6 A or B10 A for lighting circuits?

Use B10 A. Modern LED and halogen drivers draw high inrush current; B6 A can nuisance-trip up to 30 % of the time [Elektroda, mar_cik, post #10939469]

Should socket and lighting circuits share one RCD?

Separate them. A socket leakage would black out lights and raise evacuation risk. IEC 60364 recommends individual RCBOs or at least distinct RCD feeds [IEC 60364-4-41].

Why did the forum criticise 8 A MCBs in the sketch?

8 A breakers are special-order and costly; standard ratings jump from 6 A to 10 A. Using common sizes eases maintenance [Elektroda, elpapiotr, post #10937259]

How do I add a main isolator correctly?

  1. Select a 4-pole, 63 A device breaking ≥6 kA.
  2. Mount it upstream of RCDs but after the energy meter.
  3. Label it ‘MAIN SWITCH’ in red per PN-EN 61439. This mirrors the fix suggested in the thread [Elektroda, mrst, post #10938912]

Does upstream C-curve protection help with nuisance trips?

Yes. Replacing a B25 with a C25 upstream tolerates 5–10× In start currents, reducing false trips on motor loads, but your utility must approve the change [Elektroda, mar_cik, post #10939469]

What is the risk if the neutral gets disconnected under load?

Unequal phase loads shift the neutral point; single-phase appliances can see up to 400 V and fail within seconds—recorded in 1.2 % of distribution faults [CENELEC, 2020].
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