PV grounding and bonding are governed by NEC 2023 Article 250 and Part V of Article 690. Most modern PV systems are functionally grounded, so there is no grounded DC circuit conductor to bond. The array’s metal parts are tied together with an equipment grounding conductor sized under 690.45, and the reference to earth arrives through the inverter’s AC equipment grounding conductor and the building’s grounding electrode system.
Key takeaways
- Equipment grounding and system grounding are different jobs. One bonds metal so fault current reaches the source; the other gives a circuit conductor a reference to earth. Modern PV does the first and skips the second.
- “Size the GEC to the largest PV output conductor” is a leftover from solidly grounded DC arrays under the NEC 2014 architecture. NEC 2017 introduced the functional grounded PV system and the DC grounding electrode conductor stopped being the normal case.
- What you document is one continuous equipment grounding path: frames to rails, rails to rails, rails to the EGC, then back through the inverter to the premises grounding electrode system.
- UL 2703 is what makes racking count as a bonding conductor, tied to specific modules and hardware.
- Grounding is not lightning protection. That is a separate system, covered by NFPA 780.
- Inspectors check the boring things: listed hardware used per the manufacturer’s instructions, the EGC routed with the circuit conductors, separate electrodes bonded together.
What is the difference between equipment grounding and system grounding?
Equipment grounding bonds every non-current-carrying metal part together so a fault has a low-impedance path back to the source and the protective device opens. System grounding is the separate decision to tie one of the circuit conductors to earth. Confusing the two is how grounding sheets in solar plan sets end up describing an architecture the equipment does not use.
Two separate questions. What happens if a live conductor touches metal? Enough current has to flow, fast enough, to trip something – so every module frame, rail, enclosure, raceway and inverter chassis has to be electrically continuous back to the source of the fault. That applies to every PV system regardless of topology. Is a current-carrying conductor intentionally connected to earth? On a 240 V service, yes: the neutral is grounded at the service. On the DC side of a modern array, usually no – or only through a ground-fault protection device.
That second answer changed and a lot of published guidance did not. Grounding spans two of the articles in which NEC articles govern a plan set: Article 250 supplies the general rules, Part V of Article 690 modifies them for PV. NFPA publishes NFPA 70, the National Electrical Code on a three-year cycle and jurisdictions adopt on their own schedule, so the sheet has to name the cycle the AHJ adopted. Jurisdictions are spread across several NEC editions, and grounding is one place the differences bite.
Why doesn’t the old grounding electrode conductor rule fit modern PV?
Because the systems it was written for are largely gone. Under the NEC 2014 architecture a PV array was either ungrounded or had one DC conductor solidly grounded, and a solidly grounded array needed a DC grounding electrode conductor sized from 250.166 – the origin of the “size it to the largest PV output conductor” rule of thumb. NEC 2017 replaced that split with the functional grounded PV system.
The 2014 NEC said it plainly at 690.41: a system complied by being ungrounded under 690.35, by grounding one conductor of a two-wire system, or by grounding a bipolar center tap. Grounded meant solidly grounded, and 690.47 sent you to 250.166 through 250.169 – where 250.166(B) sizes the conductor no smaller than the largest conductor the system supplies.
NEC 2017 introduced a new defined term. A functional grounded PV system has an electrical reference to ground that is not solidly grounded – established through fuses, circuit breakers, resistance devices or electronic means as part of the ground-fault protection system. That is what a transformerless string inverter or a microinverter does internally. 690.41(A) in NEC 2023 permits several DC configurations accordingly, including two-wire circuits with one functionally grounded conductor and circuits not isolated from the grounded inverter output circuit. Most equipment shipping today is one of those. In practice:
- There is no grounded DC circuit conductor, so nothing for a DC grounding electrode conductor to connect to.
- The array’s reference to earth arrives through the inverter, via the AC equipment grounding conductor running with the inverter output circuit.
- 250.166 is still live code, but only for a solidly grounded DC system – legacy equipment or a retrofit onto an older array.
The failure mode is a plan set carrying a DC grounding electrode conductor callout and a dedicated array ground rod on a system needing neither – the same error as a disconnect detail drawn to an older cycle, and it tells the plan checker the sheet was copied rather than designed.
What does NEC 2023 690.43 require you to bond?
690.43 is the equipment grounding rule. Exposed non-current-carrying metal parts of PV module frames, mounting systems, electrical equipment and conductor enclosures have to be connected to the circuit equipment grounding conductor. It also governs when the mounting structure itself may serve as the bonding path.
The list is broader than installers sometimes treat it: module frames; rails, splices, clamps and roof attachments in the bonding path; combiner and junction box enclosures; inverter and rapid shutdown enclosures; metal raceways and fittings enclosing PV circuit conductors; and any other exposed metal a fault could energize.
The subsection that trips people up covers mounting systems and devices. Where racking provides grounding or bonding between modules it has to be identified for the purpose – in the field, listed to UL 2703 for bonding with the specific modules it was evaluated against. Bolting a module to a rail does not create a code-recognized bond just because both parts are aluminum.
690.43 also drives a detail that appears on inspection reports constantly: the equipment grounding conductor runs with the circuit conductors, as NEC 2023 250.134(B) and 300.3(B) also require. A conductor taking its own route raises fault-loop impedance – and it is visible from the ground.
How do you size equipment grounding conductors under NEC 2023 690.45?
690.45 sends you to 250.122, sized from the rating of the overcurrent device protecting the circuit. Where a PV circuit has no overcurrent device – common on small systems – you apply an assumed device rating derived from 690.9(B). The section has carried a 14 AWG floor for PV circuit equipment grounding conductors since at least the 2011 cycle.
Three things trip people up. The assumed-device rule: a two-string system with no fuses still needs a conductor size, and the sheet has to show what rating you applied. The 14 AWG floor: Table 250.122 will let you go smaller on paper for a low-rated circuit; 690.45 will not. Voltage drop: increases in the ungrounded conductors do not automatically pull the equipment grounding conductor up with them.
None of this separates from the current calculations feeding it. If the maximum circuit current is wrong, the overcurrent device rating is wrong and the conductor size with it – which is why the grounding sheet and the string sizing calculations have to reconcile.
When does NEC 2023 690.47 require a grounding electrode system?
690.47 requires that a building or structure supporting a PV system have a grounding electrode system installed in accordance with Part III of Article 250, with PV equipment grounding conductors connected into it. On a functionally grounded system that connection is made through the inverter’s AC equipment grounding conductor – a separate DC grounding electrode conductor is not the default.
This is where the 2017 revision did the most work. Under the older text a grounded DC PV system needed its own grounding electrode conductor tying the grounded DC conductor to the electrode system. The revised section lets the inverter’s AC equipment grounding conductor serve that role for a functionally grounded array. One path, no duplicate electrode system.
The building has to have a grounding electrode system in the first place. On older housing stock that may be a driven rod, a metal underground water pipe, or a Ufer nobody can locate. What is actually there is a site survey item, not a drafting assumption.
Auxiliary electrodes are permitted, not required. 690.47 allows additional electrodes at the array per 250.52 and 250.54 – more common on ground mounts than roofs. They do not substitute for the equipment grounding conductor, and where installed the AHJ expects them bonded to the premises electrode system rather than left as an isolated island. Ground mounts add longer runs and a racking foundation that may itself qualify as an electrode: resolve that during design, not at inspection. It is a recurring question on ground mount plan sets.
How do NEC 2023 250.66 and 250.166 size a grounding electrode conductor?
250.66 sizes the AC grounding electrode conductor from Table 250.66, based on the largest ungrounded service-entrance conductor, with hard caps depending on the electrode. 250.166 does the same job for a DC system. On a functionally grounded array you are almost always working with 250.66 at the service, not 250.166 at the array.
| Where it applies | Section | Sizing basis | Caps |
|---|---|---|---|
| AC side – service GEC | NEC 2023 250.66 | Table 250.66, from the largest ungrounded service-entrance conductor | 6 AWG Cu max to rod/pipe/plate; 4 AWG Cu max to concrete-encased; no larger than the ground ring conductor |
| Auxiliary array electrode under 690.47 | NEC 2023 250.66 | Same table and caps | The rod/pipe/plate cap applies in nearly every rooftop case |
| DC side – solidly grounded DC only | NEC 2023 250.166 | (A) through (E): no smaller than the neutral, or than the largest conductor supplied by the system, 8 AWG Cu minimum | 6 AWG Cu max to rod/pipe/plate; 4 AWG Cu max to concrete-encased; no larger than the ground ring conductor |
The caps save argument. Size straight off the table without applying 250.66(A) and you can specify a conductor several sizes larger than the code requires for a driven rod. One more Article 250 item that shows up on grounding write-ups: NEC 2023 250.64(E) requires bonding fittings where a ferrous metal raceway encloses a grounding electrode conductor – an unbonded ferrous raceway chokes the path it is meant to protect.
What does UL 2703 certification actually cover?
UL 2703 is the Standard for Mounting Systems, Mounting Devices, Clamping/Retention Devices, and Ground Lugs for Use with Flat-Plate Photovoltaic Modules and Panels. Certification evaluates bonding, grounding, mechanical loading and fire classification together, tied to the module models and hardware the system was tested with. It is what turns a rail into a code-recognized bonding conductor.
UL Solutions describes its PV mounting systems certification as covering roof and ground-mounted systems, noting that PV equipment needs proper bonding in addition to code-compliant grounding for protective devices to work. The standard also sets the rooftop fire classification. On a plan set:
- Integrated bonding is real, and bounded. IronRidge’s XR flush mount installation manual states the system conforms to UL 2703 for bonding, grounding, mechanical loading and fire classification, and may be used to ground and/or mount modules listed to UL 1703 or UL 61730. Bonding pins, bonded splices and row-to-row jumpers are all part of the evaluated assembly.
- Lug counts come from the manufacturer, not habit. That manual specifies one grounding lug per continuous bonded subarray regardless of size. Adding lugs per module is not more compliant – it makes the drawing disagree with the listing.
- WEEB washers are a listed component with their own rules. The WEEB installation instructions are explicit: tested to UL 467 and CAN/CSA-C22.2 No. 41, specific part numbers bond modules to rails while others bond spliced rails, single use only, torqued to 10 ft-lb. A reused WEEB is not a bond.
The plan set names the racking by model, names the modules it is certified with, and references the manufacturer’s instructions. Racking specified generically is one of the more reliable plan set mistakes to avoid.
How do you keep bonding continuous across rails and roof penetrations?
Continuity is an assembly property, not a component property. Every joint – module to clamp, clamp to rail, rail to splice, rail to attachment – either was evaluated as a bonding joint or it was not. The plan set shows which joints carry the bond and which are purely mechanical.
Roof penetrations get misread most often. An L-foot lagged into a rafter is a structural connection; whether it is also a bonding connection depends on whether the manufacturer’s UL 2703 certification includes that path. Many systems deliberately do not rely on the attachment, bonding rail to rail and lugging the subarray once. Rules that keep the detail honest:
- Draw the bonding path as a continuous line, from the furthest module frame to the equipment grounding conductor termination.
- Call out bonded splices where rail sections join and bonding jumpers where rows are separated. A mechanical splice is not automatically a bonded splice.
- Do not mix manufacturers within a bonded path – a clamp from one system in a rail from another voids the evaluated assembly.
- Put the manufacturer’s torque values on the sheet so the crew and the inspector work from the same number.
Penetrations also carry a structural obligation – flashing, attachment spacing, load path. Where that needs a licensed engineer it is a separate scope from the bonding detail, handled through engineering stamps.
Does grounding protect a PV array from lightning?
No, and the plan set should not imply that it does. Grounding and bonding manage fault current and hold equipment at a common potential so overcurrent and ground-fault protection can operate. Lightning protection is a separate discipline with its own standard.
That standard is NFPA 780, Standard for the Installation of Lightning Protection Systems, which sets requirements for lightning protection system design, installation and maintenance. A compliant Article 250 grounding electrode system is not a lightning protection system.
What bonding and grounding genuinely do in a storm-prone environment is narrower: they hold exposed metal at the same potential, limiting the voltage difference across equipment during a transient, and they give surge protective devices – a separate, listed component – a reference to work against. Where a site genuinely needs lightning protection, that is a designed system specified to NFPA 780 and coordinated with the array, not substituted by it.
What do AHJs check on a grounding inspection?
Less than installers expect, and more consistently. Published residential PV inspection checklists converge on the same grounding items: listed hardware used per the manufacturer’s instructions, a correctly sized equipment grounding conductor routed with the circuit conductors, separate electrodes bonded together, bonding fittings on ferrous raceways, and racking listed to the bonding attribute of UL 2703.
The City of Maitland’s residential solar PV inspection checklist is representative. Its grounding line items include:
- “Modules are bonded per manufacturer’s instructions using supplied hardware or listed equipment specified in instructions” – 110.3(B), 690.43(A)
- “Module/rack assembly is listed to bonding attribute of UL 2703” where the system is used for bonding
- “Properly sized equipment grounding conductor is routed with the circuit conductors” – 690.45, 250.134(B), 300.3(B)
- “Separate grounding electrodes, if used, are bonded together” – 690.47, 250.50, 250.58
- “Bonding fittings are used for ferrous metal conduits enclosing grounding electrode conductors” – 250.64(E)
- “Racking and PV system support structures installed and torqued per manufacturer’s instructions and approved plans”
That checklist cites the 2017 NEC – written to the cycle that jurisdiction adopted, as yours will be. Confirming the cycle before drafting prevents most of the reasons solar permits get rejected.
Note the pattern: almost every item is a documentation check as much as a field check. “Per manufacturer’s instructions and approved plans” means the inspector is comparing the roof to your sheet. The failures are rarely exotic – reused WEEBs, an unbonded splice, a lug on the wrong subarray. A pre-submittal check catches most on paper; the local AHJ quirks worth knowing catch the rest.
FAQ
Do solar panels need to be grounded?
Yes. NEC 2023 690.43 requires exposed non-current-carrying metal parts of PV module frames, mounting systems, equipment and enclosures to be connected to an equipment grounding conductor. On a functionally grounded system that path is the array’s whole grounding scheme – there is no grounded DC conductor to bond.
Does a rooftop solar array need its own ground rod?
Usually not. NEC 2023 690.47 requires the building supporting the PV system to have a grounding electrode system per Part III of Article 250, and the array bonds into it through the equipment grounding conductor. Auxiliary electrodes at the array are permitted, not required, and must be bonded to the premises electrode system.
What size grounding electrode conductor does a PV system need?
On a functionally grounded system, usually none on the DC side. The AC grounding electrode conductor is sized from NEC 2023 250.66, capped at 6 AWG copper to a rod, pipe or plate and 4 AWG copper to a concrete-encased electrode. NEC 2023 250.166 applies only to a solidly grounded DC system.
Does grounding protect solar panels from lightning?
No. Grounding and bonding manage fault current and hold equipment at a common potential so overcurrent and ground-fault protection can operate. Lightning protection is a separate system, covered by NFPA 780, Standard for the Installation of Lightning Protection Systems.
What does UL 2703 certification mean for my racking?
UL 2703 covers mounting systems, mounting devices, clamping/retention devices and ground lugs for flat-plate PV modules. It evaluates bonding, grounding, mechanical loading and fire classification, tied to the modules and hardware tested. The bonding claim holds only if you use the certified components at the specified torque.
Get the grounding sheet right before it reaches the roof
Grounding is one of the few parts of a PV plan set where the code moved and the documentation never caught up. A sheet that still describes a solidly grounded DC array, or promises lightning protection, tells the plan checker something about the rest of the package.
Avila Solar Drafting builds permit-ready plan sets in 2-3 business days, 1-2 business days for Fast Roof, to the NEC cycle the jurisdiction has adopted – with the grounding and bonding detail drawn to the racking and modules you are actually installing. Every set is designed to pass first-time review, and revisions are free for six months.
Scoping what belongs in a permit-ready plan set or a commercial solar PV design where the grounding scheme gets more involved? Call 971-410-0655.
