The short answer
Not necessarily. Modules sit in parallel, so Riso divides.
Plain English
Not necessarily. Modules sit in parallel, so Riso divides: 15 kWp at the module limit = 40 MΩ·m² ÷ 60 m² = 0.67 MΩ.
Why? Every m² adds a tiny leak path, so array Riso falls as it grows. The example is 15 kWp · 30 × 500 Wp · 60 m².
The chart in the video is the worst case (every module exactly at the limit). Real modules usually measure well above it.
But don't blame the size first. Modules usually test well above the limit: on a small roof, find the fault.
Source
Fronius white paper "DC Insulation Resistance of PV Systems", v02, 06/2026 (IEC 61215-2 MQT 15: 40 MΩ·m²; IEC 62109-2: Riso ≥ Vmax / 30 mA; 15 kWp example; presets in Appendix A)www.fronius.com ↗
Where installers ask this
- SUN2000 15KTL-M2 low insulation (r/solar)
- reddit.com/r/solar/comments/1lxgtc1/
- reddit.com/r/solar/comments/1ellz9q/
- reddit.com/r/solar/comments/1vktn59/
- reddit.com/r/SolarPakistan/comments/1uhs26h/
- Error 475 (insulation / moisture) on Fronius inverter (r/solar)
- reddit.com/r/SolarUK/comments/1qxd1vk/
- reddit.com/r/SolarDIY/comments/1mty17f/
- DC current leakage to ground detected by the inverter (r/solar)
- reddit.com/r/amberelectric/comments/1sr1ilh/
- reddit.com/r/solar/comments/1nt5mk0/
The full answer
- QS-001 · Huawei SUN2000 throws alarm 2062 Low Insulation Resistance every morning or after rain. Where do I start?
- QS-008 · Fronius state 475 / 502 insulation too low after rain. What's the procedure?
- QS-009 · Sungrow fault 039 Low System Insulation Resistance in the morning or after rain. What now?
- QS-011 · GoodWe ISO error: what insulation reading should a string have?
What's your first check on a wet-morning Riso trip?
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