Definition
A ground fault in a solar PV system is an unintended current path between an energized conductor and ground or grounded equipment. NEC 690.41(B) requires ground-fault protection that detects, indicates, and interrupts dangerous ground-fault currents.
NEC 690.41 / 690.42 / 690.45
- 690.41(B): Ground-fault protection required.
- 690.42: Equipment grounding bonding methods.
- 690.45: EGC sizing per Table 250.122.
Detection & Response
Modern inverters monitor for ground-fault currents continuously. Trip thresholds:
- Residential systems: 0.1–0.3 A.
- Commercial: 1 A.
- Utility: 5 A.
On trip: inverter disconnects affected string(s); annunciates fault; logs event.
Key Takeaways
- Ground fault = unintended current path between PV conductor and earth.
- NEC 690.41(B) mandates detection and interruption.
- Modern inverters include integrated ground-fault protection.
- Common causes: damaged backsheet, water in J-box, abraded insulation.
- Fault triggers system shutdown until cleared and verified.
Frequently Asked Questions
5 commonly searched questions about Ground Fault.
What is a ground fault?
An unintended current path between an energized PV conductor and the grounded metal of the system (frames, racking, conduit, EGC). Indicates insulation breakdown or wiring fault.
Why do ground faults matter?
Safety: ground-fault currents can shock service personnel. Fire: low-magnitude faults can heat materials. Reliability: ground faults disable strings until cleared.
What's required by NEC 690.41(B)?
Ground-fault protection that detects, indicates, and disconnects in the event of a ground fault. Modern inverters include this functionality.
How are ground faults detected?
Residual current measurement (current going out ≠ current coming back). The difference flows to ground. Detection threshold typically 0.1–1 A depending on system size.
Common ground fault causes?
Damaged module backsheet, water ingress in J-box, abraded conductor insulation, animal damage, manufacturing defect.
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