Grounding is one of the most misunderstood aspects of solar PV installation — and one of the most frequently flagged during AHJ inspections. NEC 690.41 sets the requirements for ground fault protection in PV systems, while 690.43 and 250.122 cover equipment grounding and EGC sizing.
The shift from grounded to ungrounded (transformerless) inverters changed the grounding picture significantly. Modern string inverters don’t connect either PV conductor to ground — they achieve safety through isolation monitoring instead. Understanding which type of system you’re installing determines what the code requires.
SurgePV’s solar design software helps automate compliance documentation.
Grounded vs. Ungrounded — the Modern Default
Over 95% of new US residential and small commercial solar installations use transformerless (ungrounded) string inverters or microinverters. For these systems, NEC 690.41 is satisfied by the inverter’s built-in isolation monitoring. Grounded system requirements mostly apply to legacy installations, some large commercial systems with isolation transformers, and certain utility-scale designs.
Ground Fault Protection: The Core Requirement
NEC 690.41(A) requires that all solar PV systems have ground fault protection — a mechanism to detect when a fault current is flowing through an unintended path to ground and interrupt it to prevent fire or electrocution.
Ungrounded Systems (Transformerless Inverters)
For modern transformerless inverters:
- No conductor is intentionally grounded
- The inverter continuously monitors the isolation resistance between the PV array and ground
- If isolation drops below a threshold (indicating a ground fault), the inverter shuts down and displays a fault code
- This isolation monitoring function is part of the UL 1741 listing for transformerless inverters
The installer’s responsibility:
- Verify the inverter is listed for ungrounded PV systems (the datasheet or UL certificate will state this)
- Do not accidentally ground either PV conductor — route EGC separately from the PV source circuit conductors and do not confuse the EGC with the negative conductor
- Ensure the inverter’s isolation monitoring is functioning (verified during commissioning)
Grounded Systems (With Isolation Transformer)
For systems with isolation transformers (less common in modern residential/commercial installations):
- One conductor is intentionally grounded through a Ground Fault Protection Device (GFPD)
- The GFPD monitors current in the grounded conductor
- A fault is detected when current flows in an unexpected path, triggering disconnection
Grounded systems require additional labeling per 690.5(C): conductors that are normally grounded may become ungrounded during a ground fault, creating a shock hazard. Required warning label at the inverter and service panel.
Equipment Grounding Conductor (EGC) Sizing — 690.43
All metallic parts of the PV system that are not part of the circuit conductors must be bonded together and connected to the EGC:
- Module frames
- Racking rails and posts
- Junction box enclosures
- Combiner box enclosures
- Conduit (metallic conduit is self-grounding when properly bonded)
- Disconnect enclosures
- Inverter chassis
EGC Size: NEC Table 250.122
The EGC must be sized based on the rating of the overcurrent device protecting the circuit:
| OCPD Rating | Minimum Copper EGC |
|---|---|
| 15A | 14 AWG |
| 20A | 12 AWG |
| 30A | 10 AWG |
| 40A | 10 AWG |
| 60A | 10 AWG |
| 100A | 8 AWG |
| 200A | 6 AWG |
For PV source circuits without an overcurrent device at the point of origin (e.g., a string of modules with no combiner fuse), the EGC must be at least as large as the source circuit conductors.
EGC Color Coding
The equipment grounding conductor must be identified by: green insulation, green with yellow stripe insulation, or bare copper. Never use a grounded conductor (white/gray) as an equipment grounding conductor, even in DC circuits. The EGC must be distinguished from the negative conductor in DC circuits — a common error on systems where the installer mistakes the negative bus for the EGC.
Module Frame Bonding
Module frames must be bonded to the EGC. The challenge: module frames have an anodized aluminum surface that provides corrosion resistance but also creates an electrical barrier. Bonding must pierce or bypass this anodized layer.
Listed Bonding Methods
| Method | Description | Notes |
|---|---|---|
| Grounding clips | Spring-loaded clips that pierce anodized coating at rail contact | Most common; manufacturer-listed |
| Grounding washers (Weeb) | Serrated washers that bite through anodized surface at mounting hole | Listed per UL 467 |
| Direct mounting to grounded rail | Metal-to-metal contact when racking system listing covers module bonding | Must verify with racking mfr. |
| Dedicated ground lug | Some modules have a dedicated grounding lug on the frame | Use listed lug hardware |
The bonding method must be listed — general hardware store components that aren’t UL-listed for solar bonding don’t qualify.
Racking System Listing and Module Bonding
Some racking manufacturers (Unirac, IronRidge, Schletter) include module-level bonding as part of their system listing. When the racking system is used as specified in its listing, module frames are considered bonded through metal-to-metal contact with the grounded rail without additional bonding hardware. Verify this with the specific racking manufacturer’s installation instructions.
Grounding Electrode Requirements (690.47)
The PV system must connect to the premises grounding electrode system — the same rod(s), plates, or water pipe that ground the building’s electrical service.
Connection Point
The PV system EGC connects to the grounding electrode system at:
- The main service panel grounding electrode conductor
- A dedicated grounding electrode connection point listed for PV use
- The grounding electrode directly (a second listed grounding electrode can be added if required)
Do not create a separate isolated grounding system for the PV array — the array grounding electrode must be bonded to the building’s grounding electrode system.
DC Grounding Electrode (NEC 2020)
NEC 690.47(B) requires a grounding electrode for DC systems where the voltage to ground exceeds 250V for grounded systems. For most modern ungrounded (transformerless) systems, this provision doesn’t apply because neither PV conductor is intentionally grounded.
For grounded commercial systems with negative-ground designs at 500V or higher, a DC grounding electrode is typically required. Consult the specific NEC edition adopted and the AHJ’s interpretation.
Common 690.41/Grounding Mistakes
| Mistake | Issue | Fix |
|---|---|---|
| Using unlisted bonding hardware | Not code-compliant | Use listed grounding clips, Weeb washers, or racking-integrated bonding |
| Undersizing EGC | Code violation; safety hazard | Size per NEC Table 250.122 based on OCPD rating |
| Connecting PV EGC to a separate grounding rod (isolated from building) | Violates 690.47 — must bond to building system | Connect to existing grounding electrode system |
| Confusing negative conductor with EGC in ungrounded systems | Creates incorrect grounding path | Keep EGC (green/bare) physically and electrically separate from negative conductor |
| Using green-coded wire as a circuit conductor | Creates shock hazard confusion | Green/bare/green-yellow is reserved for EGC only |
Generate Grounding Diagrams for AHJ Submissions
SurgePV’s permit packages include EGC sizing tables, bonding notes, and grounding electrode connection points on the one-line diagram — covering all 690.41 and 690.43 documentation requirements.
Book a DemoNo commitment required · 20 minutes · Live project walkthrough
Frequently Asked Questions
What does NEC 690.41 require for solar grounding?
Ground fault protection for all PV systems. Modern transformerless inverters satisfy this through built-in isolation monitoring — they detect ground faults and shut down automatically. Older grounded systems use a dedicated Ground Fault Protection Device (GFPD) in the grounded conductor.
How do I bond module frames under NEC 690.43?
Use listed bonding hardware: grounding clips, Weeb washers, or racking systems with manufacturer-listed module bonding. The bonding method must pierce the anodized aluminum surface of the module frame. Unlisted hardware from a hardware store does not qualify.
What size EGC do I need for a solar PV system?
Size the EGC per NEC Table 250.122 based on the overcurrent device protecting the circuit. A 15A fuse requires a 14 AWG copper EGC minimum; a 60A fuse requires a 10 AWG copper EGC minimum.
