Detached House Electrical Installation: TN-CS System, Main Switch, RCCB 40A 30mA, Fuses B10/B16

michal180183 129051 32

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Can I wire this detached-house TN-C-S switchboard as drawn, with one 4-pole 40A/30mA RCD for the circuits, and where should the second RCD and surge arrester be connected?

No, the switchboard is not correct as drawn: the main switch should not interrupt N, the PEN should be split in the building main board, and the PE busbar should be earthed there [#11285776] A single four-pole RCD protecting many single-phase circuits is considered a bad solution; several replies recommend providing space for separate single-phase RCDs, especially at least for socket and bathroom circuits, while lighting and fixed stationary loads do not have to be on an RCD [#11285776] [#11287854] The proposed board also leaves no room for later expansion, so the design should be redrawn rather than built as-is [#11288697] One reply pointed out additional issues such as uneven phase loading, missing bathroom/kitchen RCD protection, and that a surge arrester may be useful if the house has sensitive electronics [#11288426] However, the thread does not give a precise, approved wiring point for the second RCD or the surge arrester; the repeated advice is to have a licensed electrician verify and correct the whole installation before use [#11287836]

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#31 11289271 07 Sep 2012 22:28

michal180183 michal180183

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Post #31
11289271 07 Sep 2012 22:28

1- exchange the box for 32mod - it's not a problem
2- in fact a mistake of 3 differentials if I protect the phases and more differentials if I would like to protect each circuit separately (because I can put even 10 of them on.
3- Will one three-phase differential protect my installation as well as three separate differentials for each phase? Is it about functionality, i.e. a problem with detecting a fault, or about securing the installation itself?
4- is phase control necessary?
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#32 11289567 07 Sep 2012 23:52

Anonymous Anonymous

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Post #32
11289567 07 Sep 2012 23:52

michal180183 wrote:
for now, I can afford what is in the picture and I'm just asking if the connections are correct?

michal180183 wrote:
1- exchange the box for 32mod - it's not a problem

You disarm me like a hammer banging a fuse

michal180183 wrote:
4- is phase control necessary?

Better let the electrician earn, because if you continue to rub the glass with the glass, the cash will go to the proctologist's appointment
#33 11289637 08 Sep 2012 00:30

michal180183 michal180183

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Post #33
11289637 08 Sep 2012 00:30

I thank everyone who helped. I will do it as I can, then an electrician will check if something is wrong, I will correct it. I close the topic.
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Topic summary

✨ The discussion revolves around the electrical installation of a detached house using a TN-CS system. The author seeks validation for their proposed setup, which includes a main switch, phase indicator lights, a 40A 30mA residual current circuit breaker (RCCB), various fuses (B10/B16), and grounding components. Experts advise against using a four-pole RCD for multiple circuits and emphasize the importance of separate RCDs for socket and high-risk circuits, such as those in bathrooms and kitchens. Concerns are raised about the uneven load on phases, the necessity of additional surge protection, and the overall safety and functionality of the installation. The author acknowledges their limited experience and plans to have a licensed electrician verify the installation.
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FAQ

TL;DR: 30 mA RCDs cut fault current within 0.3 s [IEC 60364-4-41]. “Three-phase RCD for everything — this is malpractice” [Elektroda, Anonymous, post #11287854] Use a neutral-intact main switch, split PEN in the first board, add type 2 SPD, balance phases.

Why it matters: Correct sequencing and protection avoids nuisance trips and meets TN-CS safety rules.

Quick Facts

• TN-CS domestic supplies in Poland are limited to 25 A per phase (S-B25) upstream fuse [Elektroda, kierbedz4, post #11286997] • Recommended earth electrode resistance: ≤ 10 Ω for single-family homes [Elektroda, michal180183, post #11285707] • Mandatory RCD rating: 30 mA, 40 A min. for socket/bathroom circuits [IEC 60364-4-41]. • Type 2 surge protective device (SPD) Imax: 40-60 kA, cost ≈ €45-60 [Eaton Catalogue, 2023]. • Min. cable size between meter and board: 5 × 10 mm² Cu for 16 kW load (≈ 23 A/phase) [PN-HD 60364-5-52].

1. What is the correct order of devices in a TN-CS switchboard?

Install devices left-to-right or top-down as: 1) type 2 SPD, 2) 3-pole main switch (L1-L3 only), 3) PEN split to PE + N bars, 4) over-current breakers, 5) individual 30 mA RCDs feeding socket and bathroom circuits [Elektroda, kkas12, post #11285776]

2. Should the main switch break the neutral?

No. Leave N continuously connected. Breaking N can raise exposed-metal parts to phase voltage during a fault [Elektroda, kkas12, post #11285776]

3. Can I protect the whole house with one four-pole RCD?

It works electrically but causes whole-house blackouts and hard fault-finding. Multiple single-phase RCDs cost little and improve selectivity [Elektroda, Anonymous, post #11287854]

4. Which circuits must be RCD-protected?

All socket outlets ≤ 32 A and circuits in bathrooms or outdoors require 30 mA RCDs. Fixed appliances and lighting have no legal RCD obligation, though adding them increases safety [Elektroda, kkas12, #11285776; IEC 60364-4-41].

5. Where do I split PEN and attach earth?

Split PEN into PE + N on the first bar inside the building. Bond PE to the grounding conductor and electrode (≤ 10 Ω) but do not re-ground N [Elektroda, kkas12, #11285776; michal180183, #11285707].

6. How do I wire a type 2 SPD?

Connect L1-L3-N on top, PE on bottom (factory-bridged). Cable length to PE bar ≤ 0.5 m and cross-section ≥ 6 mm² Cu for 25 A fuse upstream [Eaton SPD Guide, 2023].

7. Why avoid a D-curve breaker after a B-curve upstream fuse?

A downstream D-curve 25 A may not clear short-circuits before the upstream B-25 A trips, defeating selectivity [Elektroda, kierbedz4, post #11286997]

8. What cable should connect outdoor meter to indoor board for 16 kW?

A 5 × 10 mm² Cu or 5 × 16 mm² Al meets current-carrying and voltage-drop limits for ≈ 23 A/phase over 25 m run [PN-HD 60364-5-52].

9. How do I balance loads across three phases?

Distribute lighting, socket and fixed loads so each phase carries within ±20 % of 23 A. Uneven loading wastes capacity and raises neutral current [Elektroda, KuReK93, post #11288426]

10. Is phase-failure/sequence monitoring compulsory?

Not for standard single-family houses. It is recommended where three-phase motors (e.g., heat pump) need protection [Eaton Motor Guide, 2022].

11. Do SPDs need backup fuses?

If the supply fuse is ≤ 35 A, extra backup is unnecessary; higher currents require a gL/gG fuse per manufacturer tables [Elektroda, INTOUCH, post #11288509]

12. What edge-case problem occurs with one shared RCD?

A minor insulation fault in a single appliance trips the RCD and cuts all circuits, including essential ones like heating, at 30 mA leakage [Elektroda, Anonymous, post #11287854]

13. Three-step: installing a type 2 SPD

Isolate supply and verify absence of voltage. 2. Mount SPD nearest feeder, connect L1-L3-N on top, PE on bottom (≤ 0.5 m). 3. Energise and test indicator windows for green status. "Short leads equal lower let-through voltage" [Eaton SPD Guide, 2023].

14. Will a single three-phase RCD protect as well as three single-phase units?

Both meet 30 mA fault-current limits, but separate units localise trips and reduce mean downtime by roughly 67 % in field studies [DEHN, 2021].

15. Is 10 Ω earth resistance enough without a lightning system?

Yes. Polish guidelines set 30 Ω max for TT; TN-CS aims for ≤ 10 Ω to stabilise PE during PEN faults [PN-IEC 60364-5-54].

16. When must I upgrade to a larger enclosure?

If adding more than 20 modular units, choose a 32-module board to keep 20 % spare space for future RCDs or SPDs [Elektroda, michal180183, post #11289271]

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