What are the fundamental requirements for solar grounding and bonding under the National Electrical Code? Solar PV systems require two interrelated grounding systems: Equipment Grounding (bonding all non-current-carrying metallic components such as module frames, racking rails, and inverter chassis per NEC 250.110 and NEC 690.43) and System Grounding / Grounding Electrode Conductor (GEC) connection to earth ground per NEC 250.64 and NEC 690.47.
Grounding and bonding errors represent one of the top causes of AHJ field inspection redlines. A compliant permit plan set must clearly identify conductor sizes, bonding hardware listings (UL 2703), and connection points to the building's grounding electrode system (GES).
1. Grounding vs. Bonding: Clarifying the Engineering Definitions
In electrical engineering, the terms are distinct yet complementary:
Bonding (NEC Article 100 & 250.90)
Joining metallic parts together to form an electrically conductive path that ensures electrical continuity and the capacity to conduct safely any fault current likely to be imposed. Bonding prevents lethal touch-potential voltages between adjacent metal structures.
Grounding (NEC Article 100 & 250.4)
Connecting electrical systems to the earth through a Grounding Electrode Conductor (GEC) and grounding electrode (e.g., ground rod, concrete-encased Ufer ground) to limit voltages imposed by lightning, line surges, or unintentional contact with higher-voltage lines.
2. Equipment Grounding Conductor (EGC) Sizing (NEC Table 250.122)
The Equipment Grounding Conductor (EGC) runs with circuit conductors and connects metal equipment enclosures to the grounding busbar. EGC size is determined by the rating of the overcurrent protective device (OCPD) protecting the circuit:
| Rating of Overcurrent Device (OCPD) | Minimum Copper EGC Size (NEC Table 250.122) | Typical Solar PV Application |
|---|---|---|
| 15 Amps | 14 AWG Copper | Microinverter 15A branch circuit |
| 20 Amps | 12 AWG Copper | Standard 20A microinverter / string branch |
| 30 Amps | 10 AWG Copper | Residential DC string combiner / AC disconnect |
| 40 Amps | 10 AWG Copper | 7.6 kW – 10 kW residential inverter output |
| 60 Amps | 10 AWG Copper | 11.4 kW residential / small commercial inverter |
| 100 Amps | 8 AWG Copper | 25 kW – 30 kW commercial string inverter output |
| 200 Amps | 6 AWG Copper | 50 kW – 60 kW commercial solar combiner panel |
3. UL 2703 Certified Racking Bonding Methods
In legacy solar installations, technicians were forced to run bare 6 AWG copper wire to every individual solar module frame using copper lay-in lugs, resulting in high labor costs and galvanic corrosion risks between copper and aluminum frames.
Modern plan sets utilize UL 2703 certified integrated grounding systems (such as IronRidge UFO, Unirac Solartube, or SnapNrack). These systems feature stainless steel bonding pins embedded directly into the module mid-clamps and end-clamps that pierce the anodized aluminum coating of the module frame, creating an integrated, code-compliant bonding path across the entire array rack.
4. Auxiliary Grounding Electrodes (Ground Rods) for Rooftop Arrays
A frequent question from contractors: "Does a rooftop solar array require a separate ground rod?"
Under NEC 690.47, a separate auxiliary grounding electrode is NOT mandatory for rooftop installations if an EGC is bonded to the main service grounding system. However, if an auxiliary ground rod is installed at an exterior inverter or ground-mount array, it MUST be bonded directly to the building's existing grounding electrode system to prevent differential ground potential during lightning strikes.