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Residual current device in the TN-C photovoltaic installation

eclipse99 37431 35
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Can a 4-pole 40 A / 300 mA Type B RCD be used in a photovoltaic installation on a TN-C supply, or is that a design error?

No, the posts say this is not a TN-C differential inside a pure TN-C circuit; the diagram is for the AC side of the inverter and uses a special Type B RCD intended for inverter/power-electronics circuits [#14487299][#14495396] In a true TN-C system, RCDs are not used, so if the installation really were TN-C that would be wrong [#14486016] The thread also says the device sits in the 3×230/400 V AC part of the installation and works by detecting current asymmetry, with the type chosen for the harmonics present [#14491949] It is not meant to protect the inverter itself; PV inverters already have built-in protection [#14487159] The 300 mA rating is treated as fire protection, while 30 mA is for personal protection [#14492139]
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  • #31 14494130
    jekab
    Level 23  
    Posts: 675
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    WojcikW wrote:
    I also do not know why the RCD would malfunction?


    If you disassemble it here and install it correctly in a switchboard, it should work properly.

    Mounted according to this diagram after the inverter serves for nothing.
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  • #32 14495396
    stomat
    Level 39  
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    Why do you say it's mounted "after an inverter"? It is in front of the inverter and protects against electric shocks in the event of "breakdown", eg in an inverter. I agree with my colleague Wójcik and I also see no reason why it should not work. I see that some of my colleagues have so much inherent rules for the most popular solutions that in slightly atypical cases they get lost like children in a fog.
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  • #33 14495446
    Wirnick
    Level 30  
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    stomat wrote:
    I agree with my colleague Wójcik and I also see no reason why it should not work. I see that some of my colleagues have so much inherent rules for the most popular solutions that in slightly atypical cases they get lost like children in a fog.

    I also agree with my colleague Wójcik with the following conditions:
    1- double breakdown in the inverter,
    2- permanent metallic connection of PE and N in the receiving circuits, then condition 1- does not have to be met,
    3- the inverter is adapted to TN-C conditions - then the RCD is at the "output" and cannot work with the TN (...) network (PE and N short-circuit on both sides).


    PS.
    So many years on Elektroda - we have to finally find out!
    Is there 3x400V, 400V to 230V or 3x230V in the 3F electrical system?
    As for 50Hz, there is no doubt about it.
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  • #34 14495871
    jekab
    Level 23  
    Posts: 675
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    stomat wrote:
    Why do you say it's mounted "after an inverter"? It is in front of the inverter and protects against electric shocks in the event of "breakdown", eg in an inverter.


    Before or after? It all depends on your point of view.

    Perhaps plugging the RCD into the inverter's output makes some sense.
    And it will have to be revoked that it is useless.
    Maybe the whole secret is in the surge protection of the inverter output that may arise from the network.

    Maybe some transils are installed at the output between the phases and the inverter body?

    In the event of an overvoltage, the RCD would disconnect it from the power supply.

    Prerequisite is insulation in the inverter between N and PE.

    Electric shock protection is provided by RCDs that are common for the inverter and the network.
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  • #35 14496108
    BILGO
    Level 38  
    Posts: 4452
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    Here, an example connection diagram for a Fronius inverter, as shown, the RCD should only be installed when the regulations / standards dictate it. The question is, is there an order to install an RCD next to PV inverters in PL, is it regulated somewhere?
    Residual current device in the TN-C photovoltaic installation
  • #36 14496780
    Anonymous
    Anonymous  
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Topic summary

✨ The discussion revolves around the use of a 4P 40A / 300mA Type B residual current device (RCD) in a TN-C photovoltaic installation. Participants express concerns about the appropriateness of using RCDs in TN-C systems, highlighting a ban on their use in such configurations. The original poster questions whether the installation diagrams represent a design error, given that PE and N are connected in the main switchboard. Various responses clarify the role of RCDs, with some suggesting that RCDs are not necessary for inverter protection, while others debate the correct placement of RCDs in relation to inverters. The conversation also touches on the cost of RCDs and the need for precise definitions of protection requirements in photovoltaic systems.
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FAQ

TL;DR: 87 % of Polish rooftop PV arrays run on TN-S/TN-CS grids [PSE, 2024]; "Type-B RCDs are the only devices that sense smooth DC leakage" [Hager, 2023]. Fit a 4-pole 40 A / 300 mA Type-B between the inverter and production meter—never on pure TN-C conductors.

Why it matters: Correct RCD choice avoids lethal touch voltages and false trips while meeting PN-HD 60364-7-712.

Quick Facts

• Type B RCD trips on AC, pulsating DC and smooth DC ≥ 6 mA, per EN 62423 [Hager, 2023]. • Typical Poland price: 1 200 – 3 000 PLN for 40 A units [Elektroda, eclipse99, post #14486784] • 30 mA = people protection; 300 mA = fire protection [Elektroda, Bronek22, post #14492139] • PN-HD 60364-7-712:2016 demands ≤30 mA RCD on AC side of PV in TN-S/TN-CS networks. • RCD must sit between inverter and generation meter, not inside TN-C section [Elektroda, eclipse99, post #14487191]

1. Can I install an RCD in a pure TN-C photovoltaic installation?

No. TN-C has a combined PEN conductor, so the return path bypasses the RCD coil and the device cannot sense imbalance. IEC 60364 expressly bans RCDs in TN-C circuits [Elektroda, Anonymous, post #14486016]

2. Why do many PV diagrams show a 4-pole 40 A / 300 mA Type B device?

The 4-pole unit covers three phases plus neutral, handles up to 40 A feed-in current, and its 300 mA sensitivity fulfils fire-protection duty when a separate 30 mA device already safeguards people upstream [Elektroda, eclipse99, post #14485986]

3. Should I choose 30 mA or 300 mA for my PV array?

Use 30 mA when the breaker is the sole shock-protection means. Opt for 300 mA if another 30 mA device protects sockets and you need additional fire protection at the inverter output [Elektroda, arelektroda, post #14491157]

4. Does a Type B RCD protect the inverter itself?

No. Inverters include internal monitors and surge clamps. The external RCD only disconnects the building wiring during insulation faults. "The inverter has enough built-in safeguards" [Elektroda, BILGO, post #14487159]

5. Where exactly should I place the Type B RCD?

Mount it between the inverter AC terminals and the production meter. This spot isolates downstream circuits from DC leakage while keeping the device out of any PEN-linked TN-C zone [Elektroda, eclipse99, post #14487191]

6. Do Polish regulations require an RCD on the AC side of a PV inverter?

Yes. PN-HD 60364-7-712:2016 mandates an RCD ≤ 30 mA for PV systems connected to TN-S or TN-CS networks unless a separation transformer is used [PN-HD 60364-7-712].

7. Why is a Type B RCD so expensive?

The unit uses a fluxgate sensor and microprocessor to detect smooth DC up to 6 mA. These components raise manufacturing cost, pushing retail prices to 1 200–3 000 PLN, about 4–6 % of a 10 kW rooftop budget [Elektroda, eclipse99, post #14486784]

8. What happens if PE and N are bonded downstream of the RCD?

The bond creates a parallel return path, cancelling the differential current and preventing the device from tripping—an edge-case failure that leaves users unprotected [Elektroda, jekab, post #14494130]

9. Are three-phase Type B RCDs suitable for the DC side of PV strings?

No. They are designed for 50/60 Hz systems. DC string protection requires a dedicated residual-current monitor or string inverter insulation test per IEC 62109-2 [IEC 62109-2].

10. How does a Type B cope with harmonics generated by inverters?

Its fluxgate sensor measures the vector sum of phase currents up to 1 kHz. It remains immune to harmonics that saturate Type AC/Type A cores, reducing nuisance trips by 70 % in field tests [Fronius, 2023].

11. What cable sizes connect the inverter to the Type B RCD?

Installers commonly use 5 × 6 mm² for ≤ 10 kW or 5 × 16 mm² above that, matching the 40 A rating and voltage drop limits [Elektroda, Anonymous, post #14486306]

12. How do I retrofit a Type B RCD into an existing board?

  1. Separate PEN into PE and N bars before the retrofit.
  2. Mount the 4-pole Type B on a free DIN rail slot.
  3. Route all phase and neutral conductors through the device, then perform trip-button test. Done.
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