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Sequence of protections in AC switchgear in a photovoltaic installation?

Matuesz_99 48330 13
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  • #1 18910708
    Matuesz_99
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    Hello! When assembling a photovoltaic installation, I encountered two versions of protection connections in the AC switchgear (I omit the DC switchgear). Below I have shown both versions for AC, in the first one, the circuit "goes" to the circuit breaker and surge arrester, first from the inverter, and then to the residual current device and to the home switchboard.
    In the second version, the inverter wiring first goes to the RCD and the limiter, and then to the overcurrent circuit breaker and home installation.
    Sequence of protections in AC switchgear in a photovoltaic installation?
    Is any version more correct or not at all correct?
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  • #2 18910719
    toolpusher
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    Read here:
    Link

    Also remember, if you already give a differential, type A min 100mA.
  • #3 18910881
    Jan_Werbinski
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    No difference.
    It's the SPD that is the fire risk. Do not buy. Pay more for Dehn or Phoenix Contact. Pay even more for a T1 spark gap.
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  • #4 18911228
    toolpusher
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    I live in a city with earth lines and no overhead line close by. I have an old TN-C installation where the earth electrode is taken from steel pipes of the sewage system.
    I also have an old box with old screwed fuses.
    With such an installation, as I understand it, every impulse from the network burns electronics in the house, which has not happened so far, and I live for 30 years.
    As I understand it, the requirement to install the OSD on the AC side is dictated by the standard or the art?
    If it is to be of what class and what kind? Varistor or varistor + spark gap.
    From what I have watched on the web, the vast majority of installations are based on VCX security. As I understand it, this is crap.
    I used Dehn on the DC side in my installation, but such a VCX T1 + T2 (varistor) on the AC side due to the above.
    This is a mistake?
  • #5 18912985
    Jan_Werbinski
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    You have a PV installation and probably expensive electronics at home. If you had carried out the risk analysis fairly, it would have been necessary to install LPS. If there is LPS, then you need a separation that is often difficult to achieve. Hence the T1. For T2, a varistor is enough, but T1 is just a spark gap.
  • #6 18913216
    Matuesz_99
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    Quote:
    Also remember, if you already give a differential, it is type A min 100mA.

    This RCD (SPD too) was only illustrative, usually it is 300mA

    And I have another question whether the use of RCDs is a standard requirement or common sense? Because I know a company that does not install RCDs in PV installations at all.
  • #7 18913288
    Cytro12
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    Too much faith in security is also not healthy, the risk is always there, you just need to evaluate it and this is a subjective matter.
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  • #8 18913386
    czesiu
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    Matuesz_99 wrote:
    Quote:
    Also remember, if you already give a differential, it is type A min 100mA.

    This RCD (SPD too) was only illustrative, usually it is 300mA

    And I have another question whether the use of RCDs is a standard requirement or common sense? Because I know a company that does not install RCDs in PV installations at all.

    In fact, it should be a type B RCD, because A will not turn off the direct current, and it is a protection to protect against a short circuit of the AC network with the DC installation in the event of damage to the transformerless inverter.
    RCD transformer inverters do not need, just like some transformerless inverters, equipped with a DC earth fault test system (something like an insulation control system in an IT network).

    Another matter where to install this RCD, in my opinion, it is better at the main switchboard than at the inverter. Installation in the switchgear would enable detection of damage (current leakage) of the power cable and disconnection of the faulty circuit (both during production and its absence), installation at the inverter, even when the RCD is triggered, does not disconnect the cable from the voltage.
  • #9 18913474
    toolpusher
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    Fronius recommends type A:
    Link
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  • #10 18913859
    Jan_Werbinski
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    Cytro12 wrote:
    Too much faith in security is also not healthy, the risk is always there, you just need to evaluate it and this is a subjective matter.

    Lack of faith in security is dozens of times more unreasonable. Any single mother will prove it.
  • #11 18913917
    Cytro12
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    Do you sell insurance because I hear this text every year? Do you think the more you spend it will be safer? This is not how it works, any mother will confirm it.
  • #12 18915326
    Jan_Werbinski
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    Each security measure works to some degree. For example, about 10 years ago, I bought a varistor SPD and they certainly paid off, despite the fact that they were not spark gap. I know how often I have had devices damaged before and after they were installed. This
  • #13 18915434
    Cytro12
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    I spent many times less, no device was damaged, so in my opinion I am much ahead and I do not feel particularly threatened. As I wrote, the issue of risk valuation, since you set your risk high and adjusted the security, in your opinion it paid off, for me, despite the many times lower expenditure, it also paid off because I assessed the risk as accurately lower in the supplement. Hence the conclusion that there is no point in generalizing and unnecessarily costing "in advance" only according to the needs.
  • #14 18915512
    Jan_Werbinski
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    I have an overhead line, OLED TV servers, and a lot of electronics. The SPD cost less than 5%. I prefer to save on insurance. PZU is not a provider of insurance services, but a company that pays me dividends. :)
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Topic summary

✨ The discussion revolves around the correct sequence of protections in AC switchgear for photovoltaic installations. Two configurations are presented: one where the circuit flows from the inverter to the circuit breaker and surge arrester, and another where it first goes to the residual current device (RCD) and surge protective device (SPD) before reaching the circuit breaker. Participants express that both configurations are acceptable, emphasizing the importance of using appropriate protective devices, such as type A or type B RCDs, and the necessity of surge protection to mitigate fire risks. Recommendations include using high-quality brands like Dehn and Phoenix Contact for SPDs. The conversation also touches on the subjective nature of risk assessment in installations and the varying practices among companies regarding RCD installation.
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FAQ

TL;DR: "The SPD cost less than 5%," and either AC protection sequence works; choose quality SPD and the right RCD. This FAQ shows how to place breaker, SPD, and RCD, and what RCD type to use. [Elektroda, Jan_Werbinski, post #18915512]

Why it matters: Homeowners and installers need a clear, safe way to wire PV inverter AC protections and choose correct RCD/SPD.

Quick Facts

Which order is correct for AC protections after the inverter?

Both layouts you showed are acceptable. “No difference.” Focus instead on correct device selection and quality. Prioritize a robust SPD strategy and proper coordination. Many installers favor spark-gap T1 for higher surge energy. Brands like Dehn or Phoenix Contact are common choices. Use the layout that simplifies safe maintenance and inspection. [Elektroda, Jan_Werbinski, post #18910881]

Do I need an RCD on the AC side of a PV inverter?

Often yes, especially for transformerless inverters. Type B detects smooth DC components from faulted inverters. Transformer-based inverters may not need an RCD. Some transformerless units with DC earth-fault testing may also not require one. Check your inverter documentation. Placing the RCD at the main board can protect the feeder cable. This improves fault detection on that run. [Elektroda, czesiu, post #18913386]

Type A or Type B RCD for transformerless PV inverters?

Use Type B unless the inverter maker specifies otherwise. Type A can miss smooth DC from a faulted transformerless unit. “A will not turn off the direct current.” Type B addresses this failure mode and improves safety. Confirm the inverter’s built-in DC fault monitoring features. Always size current and poles to match the feeder. Label the RCD clearly for PV use. [Elektroda, czesiu, post #18913386]

Does Fronius Symo require Type B or Type A RCD?

Fronius guidance points to Type A for Symo. Follow the manufacturer’s instruction for final selection. Match RCD sensitivity and current rating to that guidance. Ensure correct coordination with upstream protection. Document the setting on your single-line diagram. “Fronius recommends type A.” [Elektroda, toolpusher, post #18913474]

Where should I place the RCD: at the inverter or in the main switchboard?

Place it in the main switchboard feeding the inverter circuit. That way, the RCD also monitors the feeder cable. It can disconnect a damaged cable during export or idle conditions. Mounting at the inverter leaves the cable energized on faults upstream. Choose enclosure space and heat dissipation carefully. Test the RCD function after commissioning. Keep test records with the installation file. [Elektroda, czesiu, post #18913386]

When should I use a T1 spark-gap SPD on the AC side?

Use T1 spark-gap SPD when a building has LPS or separation is difficult. T1 manages higher lightning surge energy than varistors. For T2 duty, a varistor device is sufficient. Coordinate with DC-side protection to avoid overlap issues. Verify earthing and bonding before final selection. Keep leads short to reduce let-through voltage. [Elektroda, Jan_Werbinski, post #18912985]

Are varistor-only SPDs safe on the AC side?

Cheap varistor SPDs are a known fire concern. Use reputable devices and consider spark-gap T1 units. “It’s the SPD that is the fire risk. Pay more for Dehn or Phoenix Contact.” Budget devices may degrade faster under repeated surges. Verify certification and replace status indicators when tripped. Size backup fusing per the SPD datasheet. [Elektroda, Jan_Werbinski, post #18910881]

Is skipping AC SPD reasonable with underground supply and no overhead lines?

Risk depends on exposure and the value of connected electronics. One user with TN-C supply reported 30 years without electronics damage. However, that is anecdotal and does not remove surge risk. Consider the inverter, TVs, servers, and appliances at stake. Surge energy can enter through many paths, not just overhead lines. Perform a risk review before deciding to omit SPD. [Elektroda, toolpusher, post #18911228]

Do SPDs actually reduce real-world damage?

Yes, users report fewer device failures after installing SPDs. “They certainly paid off” even when using varistor units. This reflects reduced surge stress on electronics. Use coordinated stages and keep leads short for best effect. Inspect and replace end-of-life modules promptly. Log surge events if the SPD offers counters. [Elektroda, Jan_Werbinski, post #18915326]

What RCD sensitivity should I choose on the inverter’s AC side?

Follow the inverter manufacturer’s advice first. Installers often choose at least 100 mA when an RCD is used. Select the correct RCD type (A or B) per the inverter design. Ensure compatibility with any inrush or leakage characteristics. Test with the inverter both producing and idle. Record trip times and currents for compliance. [Elektroda, toolpusher, post #18910719]

Is a 300 mA RCD common in PV AC protection?

Some installations use 300 mA devices on the PV feeder. That choice reflects project-specific coordination and nuisance trip considerations. Always follow the inverter manufacturer’s RCD guidance. Consider Type B where DC components are possible. Verify discrimination with upstream protections. Document rationale on the single-line. [Elektroda, Matuesz_99, post #18913216]

How do I place the RCD so it also protects the inverter feeder?

  1. Install the RCD in the main switchboard upstream of the inverter circuit.
  2. Use Type B for transformerless inverters without DC-fault detection; Type A otherwise per OEM.
  3. Test leakage detection with the inverter on and off; log results for records. [Elektroda, czesiu, post #18913386]

Are premium SPD brands and spark-gap T1 worth the spend?

Yes, they are often a small share of system cost and improve resilience. “The SPD cost less than 5%.” Premium T1 spark-gap devices handle severe surges better. They also mitigate thermal runaway versus cheap varistors. View them as insurance for high-value electronics. Keep spare modules for quick replacement. [Elektroda, Jan_Werbinski, post #18915512]
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