NEC 250.4 grounding and bonding basics for solar

Grounding language causes more confusion on solar plan sets than any other topic, because three similar words — grounded, grounding, and bonding — describe three different jobs. NEC 250.4 is the section that states why each exists, and getting the vocabulary right is the first step to a clean permit.

What 250.4 actually says

250.4 doesn't hand you a wire size; it states performance goals. 250.4(A) covers grounded (solidly grounded) systems, and 250.4(B) covers the fault-current path. The core idea in both: metal that could become energized under a fault must be tied together and given a low-impedance path back to the source so the overcurrent device operates quickly.

If that path is missing or high-impedance, a ground fault can leave enclosures energized without ever tripping a breaker — the exact hazard the section exists to prevent.

The three words, untangled

• Grounded conductor — a normal current-carrying conductor intentionally connected to earth, most often the neutral. Many modern PV inverters are transformerless with no grounded DC conductor at all.
• Grounding conductor (the EGC) — a safety path, non-current-carrying in normal operation. It only carries current during a fault, to trip the device. See equipment grounding conductor sizing.
• Bonding — the act of connecting metal parts so they share the same potential. Racking, module frames, and enclosures get bonded together so the EGC has something continuous to protect.

Why it matters on a PV install

A rooftop array is a field of aluminum frames and steel rails sitting in the weather. Every one of those parts must be bonded — usually with listed grounding lugs, WEEBs, or bonding clips rated for the specific module and rail — and tied back through the EGC to the grounding system.

• Listing matters. Aluminum-to-steel and outdoor connections corrode; use hardware listed for the metals and environment.
• Continuity matters. A rail splice or a slip-fit joint may not be electrically continuous — bond across it.
• The electrode still applies. The grounding electrode conductor (GEC) ties the system to the earthing electrode; that is a separate conductor sized under 250.66. See GEC sizing for that table.

The functional-vs-solidly-grounded wrinkle

Older grounded-DC PV systems tied one DC conductor to ground through a fuse or link. Most modern transformerless inverters are "functionally grounded" — there is no solidly grounded DC conductor at all; the inverter monitors the array for ground faults electronically. That doesn't remove your grounding duty: the equipment (frames, rails, enclosures) still must be bonded and connected to the grounding system exactly as 250.4 demands. Only the current-carrying grounded conductor may be absent.

What a reviewer looks for

The one-line should show the EGC, the bonding method for the array, and the connection to the grounding electrode system. A plan that labels the neutral as "ground," omits the array bonding detail, or sizes the array grounding conductor from the wrong table gets corrected. Reviewers also check that the bonding hardware is listed for the specific module frame and rail — a generic lug on an anodized frame is a common red-line.

Grounding requirements and DC-conductor treatment differ across NEC editions and inverter topologies. Confirm the enforced code and local amendments with your AHJ, and have a licensed electrician or PE review, sign and stamp the design before filing or energizing. For deeper dives, browse our reference library.

Educational reference, reviewed 2026-07. A design aid, not a substitute for a licensed electrician or PE. Confirm the enforced NEC edition and local amendments with your AHJ.