NEC 690.11 DC arc-fault protection, explained

A series DC arc fault is one of the more dangerous failures on a PV array: a loose connector or cracked conductor can sustain a high-temperature arc without tripping ordinary overcurrent protection, because the current stays within normal range. NEC 690.11 exists to catch that hidden failure mode before it starts a roof fire.

What the rule actually says

690.11 requires that PV systems with DC circuits operating at 80 volts or more between any two conductors be protected by a listed DC arc-fault circuit interrupter (AFCI) or an equivalent listed component. The threshold matters: a low-voltage circuit below 80 V DC falls outside the mandate, but nearly every series string on a residential roof exceeds it.

The protective device has to do three things:

• Detect the characteristic signature of a series arc fault.
• Interrupt or de-energize the arcing circuit.
• Indicate that a fault has occurred (a latching indicator or annunciation) so it is not silently reset.

Series vs parallel arcs

The rule targets series arc faults specifically — the kind caused by a broken conductor or a poorly seated MC4 connector in the current-carrying path. This is why torque and proper connector crimping matter so much during installation. A parallel arc (conductor-to-conductor or conductor-to-ground) is generally addressed by insulation and grounding, though modern listed AFCI/GFDI combinations watch for both.

How inverter topology changes the picture

Where the arc-fault detection lives depends entirely on how the DC is arranged:

• String inverters: the AFCI is built into the listed inverter, watching each DC input. This is the classic case 690.11 was written around.
• DC optimizers (SolarEdge, Tigo): the string still carries meaningful DC voltage, so the listed inverter still provides AFCI on the string.
• Microinverters (Enphase and similar): the module-level unit converts to AC right at the panel. The high-voltage DC never leaves the module assembly, so the array circuits are AC and a separate DC AFCI is not applicable.

Why plan reviewers care

A reviewer confirms that the inverter or combiner listed on the one-line carries AFCI, and that the DC operating voltage is disclosed so the 80 V threshold is clearly met or exempted. Because AFCI and ground-fault (GFDI) functions are often bundled in the same listed device, the drawing should not imply the two are separate boxes when they are one. Getting this wrong is a common correction — see why solar permits get rejected for the recurring themes.

Arc-fault protection also pairs conceptually with 690.12 rapid shutdown: one limits the arc energy, the other limits what a firefighter faces. Both are safety-of-responder rules that a reviewer expects to see reflected on the plan.

Remember that OneLine Studio is a design aid, not the authority having jurisdiction. Confirm the enforced code edition and any local amendments with your AHJ, and have a licensed electrician or PE review, sign and stamp the set before you file or energize. For the underlying conductor rules that pair with arc-fault protection, see our NEC reference hub.

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.