PV System Grounding Electrode Conductor per NEC 690.47

Why this matters

The grounding-electrode conductor (GEC) on a PV system is the single most-misunderstood section of NEC 690. Designers default to whatever the previous job had, inspectors flag installs for the wrong reason, and the actual code path is simpler than the lore suggests. NEC 690.47 went through significant restructuring in the 2017 and 2020 cycles; the 2023 code now reads more cleanly than ever. This is the working reference.

What 690.47 actually requires

NEC 690.47 requires that a building or structure supporting a PV array have a grounding electrode system installed in accordance with Article 250, and that the PV array's equipment grounding conductors connect to it. The subsection lettering inside 690.47 has moved between cycles, so cite the section and read the subsections in the edition your AHJ has adopted rather than quoting a letter from memory.

Read carefully: the PV system uses the existing premises grounding electrode system. The PV does not require a separate, isolated electrode unless the structure does not already have one. The most common field misconception is that the array requires a dedicated ground rod; it does not, on a building with an existing service-electrode system.

The bonding path

The bond from the PV system to the premises grounding electrode system runs through the equipment-grounding conductor (EGC) of the PV circuits. The EGC is sized per NEC 250.122 based on the overcurrent device protecting the circuit. The EGC terminates at the AC equipment-ground bus of the panel or service where the PV interconnects. From that bus, the building's existing grounding-electrode conductor carries to the electrode.

In other words: the PV ties to the building ground through the AC interconnection. A separate grounding-electrode conductor from the array to a dedicated rod is not required if the building has a code-compliant electrode system at the service.

When a separate PV electrode is required

Where there is no existing electrode system at the structure, which is the normal case for a stand-alone ground mount that is not on a building, one gets installed per Article 250 Part III. This applies to:

• Ground-mounted arrays on agricultural or industrial sites with no building service nearby
• Off-grid arrays at a remote cabin where the cabin electrode system is itself questionable
• Mid-array combiner boxes that meet the definition of a separate structure under NEC 225 and 250.32

For most rooftop residential and commercial PV, the building has a service-electrode system at the meter, and the PV bonds through the AC EGC to that system. No new rod needed.

EGC sizing per NEC 250.122

The EGC for PV equipment-grounding is sized per NEC 250.122 based on the overcurrent device protecting the circuit:

Read Table 250.122 by the rating of the overcurrent device, and where your OCPD rating is not a row in the table, use the next row UP. Copper:

• 15 A: 14 AWG
• 20 A: 12 AWG (this is its own row; 15 and 20 are NOT the same size, and merging them is how a 20 A circuit ends up with a 14 AWG ground)
• 30 A and 40 A: no row of their own, so take the 60 A row, 10 AWG
• 60 A: 10 AWG
• 100 A: 8 AWG
• 200 A: 6 AWG

NEC 250.120(C) keys on the size of the EGC itself, not on the size of the circuit conductors: an equipment grounding conductor smaller than 6 AWG has to be protected from physical damage by a raceway or cable armor, except where it runs in a hollow space of a framing member. So a 10 AWG EGC stapled to the underside of a rooftop module is unprotected and non-compliant no matter what the source-circuit conductors are.

DC vs AC grounding under 690.41

NEC 690.41 governs the DC system-grounding configuration. Modern PV systems are almost universally functionally-grounded or ungrounded; transformerless inverters require an ungrounded DC system per the inverter manufacturer's instructions. The DC system in this case is not connected to ground; the AC output side is the grounded reference.

This is a change from pre-2017 PV practice. Older systems with center-tap or single-point DC grounding required a DC grounding-electrode conductor sized per NEC 690.47(D) (since deleted in 2017). Modern systems do not require this; the AC EGC handles the entire grounding requirement.

If a designer encounters an existing pre-2017 PV system being retrofitted, the existing DC-grounding scheme should be preserved or replaced with a modern transformerless inverter and matching DC-grounded-or-ungrounded scheme. Do not partial-modernize one and leave the other.

Module frame bonding

Every module frame must be bonded to the equipment-grounding system via a listed bonding means. Three acceptable methods:

• Integrated grounding mid-clamps (IronRidge UFO, S-5! Solar, etc.): the clamp pierces the module frame anodizing and contacts the aluminum, achieving a bond as part of the standard module-attachment hardware
• Wire EGC (10 AWG copper) routed module-to-module via lay-in lugs (Ilsco GBL-4DBT, etc.) bonded to each frame
• Grounding washers between the module frame and the rail with a separate continuous EGC

The integrated grounding clamp is the modern standard. Verify the clamp manufacturer's listing covers the specific module frame (Q-Cell, REC, LG, etc. - not every clamp is listed for every frame).

The bond from rails to building steel or ground

The rails carry the EGC bond from the last module in the array to the AC junction box. The rail-to-rail bond uses a listed splice (IronRidge bonding hardware, SnapNRack bond clip). The rail-to-EGC connection uses a listed lug on the rail flange. The EGC then drops to the array junction box and runs with the source-circuit conductors to the inverter.

NEC 690.43 permits the array's mounting structure to serve as the equipment bonding path where the mounting system and its devices are listed and identified for that purpose. In practice, the standalone EGC is run alongside the source-circuit conductors for the inspector's visual confirmation; relying on rail bonding alone passes code but invites RFIs.

Common errors

• Designer installs a new ground rod at the array for a rooftop residential PV. Not required and not harmful, but the new rod must be bonded to the existing service electrode per NEC 250.50 (single grounding-electrode system per structure). A new rod left unbonded creates a step-voltage hazard during a fault.
• Designer uses bare aluminum EGC on a rooftop run. 250.120(C) requires any EGC smaller than 6 AWG to be protected from physical damage, bare or not; separately, bare aluminum is corrosion-prone in contact with copper or steel hardware and is a poor choice in a wet rooftop environment. Use insulated EGC, or bare copper in conduit.
• Designer omits the rail-to-frame bond and relies on the metallic continuity of the rail anodizing. Anodizing is non-conductive. The bond is via a listed clamp that pierces or scrapes through the anodizing, not via incidental metal-to-metal contact.
• Designer installs a transformer-isolated inverter and continues to ground the DC negative. Verify the inverter type; modern transformerless inverters require ungrounded DC.

References

• NEC 2023 Section 690.41 (PV system DC circuit grounding configuration)
• NEC 2023 Section 690.43 (PV equipment grounding)
• NEC 2023 Section 690.47 (grounding electrode system)
• NEC 2023 Section 250.122 (equipment-grounding conductor sizing)
• IEEE 1547-2018 (interconnection requirements including grounding)