DC insulation resistance degradation
Falling insulation resistance on the DC side — a safety-critical fault.
DC insulation (Riso) degradation is a drop in the resistance between the PV array’s live conductors and ground, usually from water ingress, damaged backsheet, or abraded DC cabling. It is safety-critical: low Riso trips the inverter (e.g. Huawei SUN2000 code 2002) and, if ignored, raises arc and shock risk.
Symptoms
- Morning inverter trips that clear as the array dries and warms.
- Insulation-resistance alarms clustered after rain or high humidity.
- A specific combiner or string repeatedly implicated.
SCADA signatures
- Riso readings falling toward the inverter’s trip threshold (often 1 MΩ class).
- Trips correlated with humidity/rainfall and time-of-day (dawn).
- Repeating fault code on the same MPPT — e.g. Huawei 2002 low insulation resistance.
Root cause
Water ingress at MC4 connectors or junction boxes, backsheet cracking, rodent or abrasion damage to DC cable, or a degraded module laminate. The fault is often intermittent — worst when wet, recovering when dry — which is exactly why it gets dismissed.
Financial impact
Beyond the lost production during each trip, declining Riso is the leading indicator of an insulation failure that can cause an arc-fault fire. The cost of acting is one inspection; the cost of ignoring it is open-ended.
How NuraVolt detects it
NuraVolt trends Riso per combiner and correlates trips with weather, so an intermittent dawn-only fault is surfaced as a degrading trend rather than dismissed as noise. It maps OEM fault codes (e.g. Huawei 2002) onto the same insulation signature for cross-vendor consistency.
Frequently asked questions
See also
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