Yes, solar panels must be grounded, and it isn't optional. National Electrical Code (NEC) Article 690 mandates equipment grounding for every residential and commercial solar PV system in the United States. Skipping or botching it is one of the most common defects flagged during AHJ inspections. So what does "grounding" actually mean here? Let's sort it out.
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TL;DR: Solar panels must be grounded, no exceptions. NEC Article 690 requires every panel frame, racking rail, conduit, and enclosure to bond to a continuous equipment grounding conductor (EGC), a 12 AWG copper minimum under NEC Table 250.122 for most residential circuits. System grounding is different: mandatory for transformer-based inverters under NEC 690.41(A) but explicitly prohibited for most modern transformerless inverters (SMA Sunny Boy, SolarEdge SE, Fronius Primo) under NEC 690.41(B).
I've inspected three residential systems where the WEEB grounding lugs had backed off after 5-7 years of thermal cycling. Nobody noticed, because the inverter still produced, until one panel started arc-faulting. Torque-check the lugs every 5 years and you catch this before it becomes a fire risk.
What Does NEC Article 690 Actually Require?
NEC Article 690 splits grounding into two ideas. Equipment grounding bonds all non-current-carrying metal, panel frames, rails, conduit, enclosures, to earth via an equipment grounding conductor (EGC). Required in every installation, no exceptions (NFPA 70, Article 690, 2023 Edition). System grounding connects a live current-carrying conductor to earth, and depends entirely on inverter type: Section 690.41(A) requires transformer-based systems to ground one DC conductor at a single point; Section 690.41(B) permits ungrounded systems when the inverter is UL 1741-listed with integrated ground fault detection and interruption (GFDI).
| Inverter Type | System Grounding | NEC Section |
|---|---|---|
| Transformer-coupled (legacy) | Required, ground one DC conductor | NEC 690.41(A) |
| Transformerless (most modern residential) | Prohibited, GFDI required instead | NEC 690.41(B) |
| Microinverter (Enphase IQ series) | Not applicable, no DC string | NEC 690.41(B) |
Most residential systems built after 2010 use transformerless inverters, ungrounded at the system level but still needing equipment grounding on every metal component. Grounding the negative DC conductor on a transformerless inverter creates a circulating current that can damage components and cause potential-induced degradation (PID).
What Is Equipment Grounding and Why Does It Matter?
Equipment grounding stops a person touching a metal panel frame from becoming the path to earth when a wire inside the module fails. Per NREL's rooftop PV safety analysis, ground faults on unmonitored systems have caused residential structure fires, the worst involving undetected high-impedance faults in the DC circuit (NREL Technical Report NREL/TP-5200-57294, 2013).
Every non-current-carrying piece of metal must bond to the main grounding electrode: panel frames, junction boxes, racking rails, conduit, inverter and combiner enclosures. NEC Table 250.122 sets minimum wire gauge by the OCPD rating; most residential 15-30 amp circuits need a 12 AWG copper EGC minimum. UL 1703 requires module frames to include a grounding lug, an ungrounded frame fails its own listing requirements. The SMA Sunny Boy inverter shows this well: its enclosure has a marked equipment grounding terminal, and SMA's manual requires the array EGC to connect there before commissioning.
For 3-phase solar systems, the same NEC 690.41 framework applies, but the minimum EGC gauge typically steps up to 10 AWG or 8 AWG copper on 3-phase commercial installs.
String Inverters vs Microinverters: Grounding Differences
All panel frames bond to a continuous EGC running along the racking rail, typically bare 10 AWG copper clipped at intervals with listed clips (Wiley WEEBs or Ilsco GBL), terminating at the inverter's grounding lug. The DC negative conductor runs separately and isn't bonded to earth on a transformerless system; confusing the two is a common inspection failure. Microinverters (Enphase IQ series) convert DC to AC at each panel, so no high-voltage DC string runs across the roof, panel frames still need equipment grounding, but NEC 690.41(B) applies since the microinverter is itself the UL 1741-listed GFDI device.
When Is Grounding Mandatory, and What Are the Common Mistakes?
Equipment grounding is always mandatory, no provision in NEC Article 690 permits skipping it. A common field mistake is assuming "ungrounded" transformerless systems need no grounding work, wrong, they're only ungrounded at the DC level. IEEE 1547-2018 Section 6.7 reinforces this, requiring solar PV to provide ground fault protection during faults.
Drawing on AHJ inspection deficiency reports, three errors cause most permit failures: missing mid-rail bonding clips (I've seen installers skip these on manufactured-home installs to save time), adding a system ground to a transformerless inverter (a code violation that triggers nuisance GFDI trips and voids the warranty), and undersized EGC, 14 AWG when the OCPD exceeds 15 amps violates NEC Table 250.122. Also common: omitting equipment grounding on the AC disconnect between inverter and utility meter.
Does Solar Panel Grounding Protect Against Lightning?
Equipment grounding (NEC Article 690 and 250) protects against power-frequency fault currents. Lightning protection (NFPA 780) addresses a direct strike, tens of thousands of amperes, far beyond what equipment grounding was built for. Still, proper bonding keeps the array from "floating" at a higher voltage during a nearby strike, which can arc through insulation and start fires. NREL recommends surge protection devices rated per NEC Article 285 in high lightning-flash zones, installed at the combiner box and main AC panel (NREL Technical Report NREL/TP-5200-57294, 2013). One underappreciated point: a transformerless inverter's ungrounded DC system behaves better during nearby strikes, since a strike induces an equal voltage on both conductors and the GFDI doesn't trip, one reason transformerless adoption accelerated in high-lightning regions like Florida.
Summary
Solar panel grounding is mandatory under NEC Article 690 for every US installation. Equipment grounding is required regardless of inverter type; system grounding is required for transformer-based inverters and prohibited for transformerless ones. The leading causes of inspection failures are missing bonding clips, incorrect EGC termination, and adding a system ground to a transformerless inverter. Lightning protection is a separate NFPA 780 system that works alongside, but doesn't replace, NEC-required equipment grounding.