Solar Module Frame Bonding: NEC 690.43 & UL 2703 Methods

Definition

Module frame bonding is the electrical connection of all PV module aluminum frames to the equipment grounding conductor (EGC), providing a safety ground path. Required by NEC 690.43; commonly accomplished via UL 2703 listed racking systems.

Key Takeaways

Module frame bonding = electrical ground path for module frames.
Required by NEC 690.43.
UL 2703 racking provides integrated bonding.
Connects to EGC for shock safety.
Documented on the SLD.

Why the Frame Needs a Ground Path

Every PV module has an aluminum frame sitting right next to insulated DC conductors and connectors. Insulation on any of those leads can degrade over years of thermal cycling and UV exposure, and once it fails, the metal frame can become an energized, touchable surface. Bonding ties every module frame in the array — not just the array boundary — to the equipment grounding conductor (EGC), so a fault current has a continuous, low-impedance path back to the source instead of stopping at an isolated, live frame. That continuous path is also what lets upstream overcurrent protection or ground-fault detection actually see and clear the fault.

How Bonding Is Implemented

NEC 690.43 does not mandate one hardware solution, it just requires a bonding path that meets the code’s continuity and sizing rules. In practice, most systems use one of three approaches:

UL 2703 listed racking — the rail and clamp system itself is tested and listed with integrated frame-to-rail and rail-to-rail bonding, which is why it is the default choice on most commercial and utility-scale arrays.
Copper lay-in lugs with through-bolts — a discrete bonding jumper is lugged directly to a drilled or through-bolted point on each frame.
Bonding washers (e.g., WEEB-style) — a serrated washer under the module-to-rail fastener bites through the frame’s anodized coating to make the ground connection without a separate jumper at every module.

Whichever method is used, the bonding scheme and jumper sizing need to show up on the electrical single-line diagram and grounding details, since that is what a plan reviewer or inspector checks the installed array against.

Module frame bonding is one piece of a broader grounding and safety picture that also includes the equipotential bonding between racking, module frames, and other array metalwork, and the sizing of the EGC itself back to the grounding electrode system. Once bonded, the ground path from the array typically terminates near the combiner box, where it is documented alongside conductor and overcurrent protection details. For teams assembling that documentation package for a permit set, our breakdown of solar SLD software covers how NEC-compliant single-line diagrams — including grounding and bonding call-outs — get auto-generated rather than redrawn by hand for every project.

Frequently Asked Questions

5 commonly searched questions about Module Frame Bonding.

What is module frame bonding?

Electrical connection of all module aluminum frames to ground. Required by NEC 690.43 for shock and fault current path.

Methods?

UL 2703 listed racking with integrated bonding (most common). Cu lay-in lugs with through-bolts. Bonding washers (e.g., WEEB).

Why does an aluminum module frame need to be grounded at all?

A PV module frame is a conductive metal enclosure sitting inches from energized DC circuits. If insulation on a module lead or connector fails, the frame can become energized. Bonding every frame to the EGC gives that fault current a low-impedance path back to ground so an upstream fuse, breaker, or ground-fault protection device can clear it, instead of leaving the frame live and touchable.

Is a UL 2703 racking system required, or can bonding be done another way?

UL 2703 listed racking is the most common route because the rail-to-module and rail-to-rail bonding is already tested and listed as part of the racking system, which simplifies the inspector sign-off. It is not the only method — lay-in lugs with through-bolts and bonding washers such as WEEB washers are also NEC 690.43-compliant, provided the connection is documented and the bonding path is continuous.

Where does module frame bonding get documented on a project?

Bonding method, jumper sizing, and the ground path back to the equipment grounding conductor are called out on the electrical single-line diagram (SLD) and grounding detail drawings, since that is what the inspector and utility reviewer check against during plan review.