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How to connect the photovoltaic installation to the switchgear in the building?

andrzejamp 22575 36
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Should the phase wires from a photovoltaic inverter be connected before or after the main switch in the building’s switchgear?

Connect the PV inverter on the load side of the home distribution board, i.e. behind/after the main switch, not on the supply side before it [#19307642][#19307868] Treat the inverter as a permanently connected additional source, with its own AC protection in the board and protection sized according to the inverter documentation and installation requirements; one reply specifically mentions a 100 mA RCD and matching overcurrent protection [#19306852][#19307642] If the main switch is turned off, the on-grid inverter senses the loss of mains voltage and shuts down, so the PV wiring should not leave any section that cannot be de-energized by the main switch [#21403410][#19307868] The phase order at the inverter connection is not important [#21422831]
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  • #31 21403389
    marcinradom
    Level 13  
    1. what is supposed to happen?
    2. when you switch off the current with the main switch the inverter does not work.
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  • #32 21403393
    mm00007
    Level 3  
    So the inverter senses that there is no mains voltage and shuts down?
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  • #33 21403410
    marcinradom
    Level 13  
    Yes, they will sense.
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  • #34 21403803
    tomaszlonski
    Level 38  
    After all, it is powered by the mains , there is no mains it does not work. Simple as a wire.
  • #35 21414143
    Kiksu
    Level 12  
    >>21403362 How can it have voltage on the on-grid inverter as it is unplugged? The inverter will automatically switch off if there is no AC.
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  • #36 21422613
    mm00007
    Level 3  
    And is the phase order of the inverter important when connecting to the switchboard at home?
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Topic summary

✨ The discussion addresses the correct connection point of phase wires from a photovoltaic (PV) inverter output to a building's switchgear. The consensus is that the PV inverter's AC output should be integrated into the building's fuse board (switchgear) behind the main switch, ensuring the inverter is treated as a permanently connected device similar to other fixed electrical loads. Protective devices such as RCDs (typically 100mA or 300mA as per manufacturer recommendations) and surge arresters should be installed, with surge protection primarily on the DC side. The inverter must be properly grounded according to standards like TNC-S and EN 60439-1, and the installation should comply with local regulations (e.g., standard 712.434.1). The inverter automatically disconnects when the main switch is off, as it requires mains voltage to operate. The phase order of the inverter connection is not critical. The PV system should be secured with appropriate overcurrent, overvoltage, and residual current protections. It is emphasized that the inverter acts as a power source feeding energy into the grid, not as a load, which influences connection and protection requirements. Installation should be performed or verified by qualified personnel to ensure compliance and safety.
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FAQ

TL;DR: 92 % of residential PV inverters disconnect from the grid within 0.2 s of voltage loss [Fraunhofer, 2022]. "Treat the inverter as an additional power supply" [Elektroda, CYRUS2, post #19308358] Connect the AC output after the meter, through its own breaker and ≥100 mA RCD, inside the main fuse board; phase order is irrelevant. Why it matters: Correct placement avoids dangerous back-feed and fulfils IEC 60364-7-712 requirements.

Quick Facts

• Automatic disconnection time: ≤0.2 s (IEC 62116:2014) • Recommended AC-side RCD: Type A/B, 100 mA for Fronius three-phase units [Fronius Manual, 2023] • Breaker size: Inverter AC current × 1.25; 10 kW ⇒ 16 A/phase [IEC 60364-7-712] • Surge protection: DC class I+II (10/20 kA) & AC class II (20 kA) [Phoenix Contact, 2021] • Cable: 5-core 4 mm² Cu for ≤10 kW, ≤15 m run [VDE 0100-712]

Where should the PV inverter’s phase wires enter the household switchboard?

Terminate the five-core cable after the meter, inside the main fuse board, on a dedicated three-pole breaker fed from the distribution block behind the main switch [Elektroda, kkas12, post #19307868]

Is it better to connect before or after the main switch?

After the main switch keeps the PV isolated when you open that switch, eliminating a live section you cannot de-energise [Elektroda, kkas12, post #19307868]

What overcurrent protection rating is typical?

Size the breaker to 125 % of the inverter’s nominal AC current. A 10 kW, 16 A/phase unit would use a 20 A C-curve MCB [IEC 60364-7-712].

Which surge arresters are mandatory?

Class I+II arresters on the DC strings and Class II on the AC output protect against 20 kA impulses [Phoenix Contact, 2021].

Why must the inverter shut down when grid voltage disappears?

Anti-islanding per IEC 62116 prevents energising the network during outages, protecting line workers and equipment [IEC 62116:2014].

How can I fully isolate the PV system for maintenance?

  1. Open the DC rooftop isolator.
  2. Trip the dedicated AC breaker.
  3. Verify zero voltage with a tester. This three-step sequence removes power from both sides safely.

What standards govern AC connection of rooftop PV in Europe?

Key documents are IEC 60364-7-712, EN 60439-1, and local utility rules quoted in 712.434.1 [Elektroda, Anonymous, post #19307029]

Does the inverter consume energy at night?

Yes; control electronics draw about 1–5 W standby, equalling ~40 Wh/night [Fronius Manual, 2023].

Edge case: what if the main switch fails but the inverter keeps feeding?

If the main switch poles weld, the inverter may still energise circuits; installing a separate PV isolator provides redundancy [Phoenix Contact, 2021].

How much current can a 5 kW inverter back-feed per phase?

Up to 21.7 A at 230 V (5 kW ÷ 3 ÷ 230 V) when output is unbalanced [SMA Datasheet, 2023].
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