What Is NEC Article 690?

NEC Article 690, "Solar Photovoltaic (PV) Systems," is the section of NFPA 70 (National Electrical Code) that governs the installation of solar PV systems — from residential rooftop systems to commercial ground-mount arrays. It covers DC and AC circuit requirements, disconnecting means, grounding, arc fault protection, and the rapid shutdown requirements that protect firefighters from energized PV circuits on building rooftops.

PV System DC Circuit Sizing

PV source circuits (the wiring between modules) are sized using NEC 690.8. The maximum current for a PV source circuit is calculated at 125% of the module short-circuit current (Isc) multiplied by 1.25 for the continuous current correction:

Conductor ampacity ≥ 1.56 × Isc

The 1.56 factor = 1.25 (irradiance correction) × 1.25 (continuous load correction, per NEC 690.8(A)(1)).

For a module with Isc = 10A: conductor ampacity ≥ 15.6A — a 10 AWG THWN-2 conductor (30A ampacity at 90°C) installed in conduit is typical.

PV System Disconnects (NEC 690.13 and 690.15)

Every PV system must have a means to disconnect all current-carrying conductors from the point of interconnection with other systems. For a grid-tied system, the inverter output disconnect and the utility disconnecting means serve this function. For larger systems (over 100V DC), a DC PV disconnect is required between the array and the inverter.

The disconnecting means must be listed, accessible, and lockable. For systems with rapid shutdown requirements, the disconnect activates the shutdown sequence when opened.

Rapid Shutdown (NEC 690.12)

Rapid shutdown protects firefighters from high-voltage DC circuits on rooftops during a fire response. The 2017 and later NEC requires that PV systems on buildings have a rapid shutdown system that reduces voltage on conductors inside the building array boundary to 30V or less within 30 seconds of initiating shutdown. The array boundary is typically defined as within 1 foot of the roof and in the building interior.

The most common rapid shutdown implementation is module-level power electronics (microinverters or power optimizers) that de-energize each module individually when the rapid shutdown initiator (a dedicated switch at the service entrance) is activated. The Sunspec Alliance defines communication protocols for rapid shutdown systems.

Arc Fault Protection (NEC 690.11)

DC arc faults — arcs in PV DC wiring from damaged cables, loose connections, or equipment failure — can sustain themselves at high temperatures and ignite fires (unlike AC arcs, which self-extinguish at zero crossings). NEC 690.11 requires arc fault circuit interrupters (AFCIs) on PV source and output circuits operating at over 80V. Many modern string inverters have built-in DC AFCI; standalone DC AFCI devices are available for older systems.

Grounding and Bonding

PV system grounding follows NEC Article 250 with specific guidance in Article 690. Ungrounded PV systems (systems without a grounded DC conductor) are now the norm for systems using transformerless inverters — this configuration is more efficient but requires specific equipment designed for the ungrounded topology. Equipment grounding conductors (EGC) must bond all metal PV equipment (module frames, racking, inverter enclosures) to the system ground. Ground-fault protection (GFP) is required per 690.41 to detect and interrupt DC ground faults.