19.5 Solar Photovoltaic Systems (Article 690)

Why PV is tested

DLI's knowledge areas include solar photovoltaic systems: disconnecting means; wiring methods. Minnesota's cold winters make the voltage correction a common exam calculation, because module voltage rises as temperature drops.

Maximum voltage (690.7)

The maximum PV source circuit voltage is the sum of the series-connected modules' open-circuit voltage (Voc), corrected for the lowest expected ambient temperature. Use the module manufacturer's temperature coefficient of Voc when available, or the correction factors in Table 690.7(A) for crystalline and multicrystalline silicon modules. For systems of any size, a licensed professional engineer may also calculate the voltage using an industry standard method; the 2026 NEC removed the former 100 kW threshold for that option and clarified that 690.7(A) applies to dc voltages.

Minnesota example: each module has a Voc of 49.5 V at 25°C and a temperature coefficient of −0.28%/°C. The lowest expected ambient temperature at the site is −30°C, a difference of 55°C.

1. Correction: $1 + 0.0028 \times 55 = 1.154$.
2. Corrected Voc per module: $49.5 \times 1.154 = 57.1$ V.
3. A string of 12 modules: $12 \times 57.1 = 685$ V, which exceeds 600 V for a one-family dwelling.
4. A string of 10 modules: $10 \times 57.1 = 571$ V, which is acceptable.

Current and conductor sizing (690.8)

Example: a string with modules rated Isc = 11 A. Maximum current $= 11 \times 1.25 = 13.75$ A. Minimum conductor ampacity before adjustment $= 13.75 \times 1.25 = 17.2$ A, so 125% is applied twice to the Isc (156%).

Arc-fault protection (690.11)

PV systems with DC circuits operating at 80 V or greater between any two conductors, on or penetrating a building, must be protected by a listed PV arc-fault circuit interrupter or other component listed to provide equivalent protection, to detect and interrupt arcing faults in the DC circuits.

Rapid shutdown (690.12)

PV system circuits installed on or in buildings must include a rapid shutdown function to reduce shock hazard for firefighters.

Disconnecting means (690.13 and 690.15)

• PV system disconnecting means (690.13): must disconnect the PV system from all other systems, be installed at a readily accessible location, be permanently marked "PV SYSTEM DISCONNECT" or equivalent, and indicate whether open or closed. Where line and load terminals may both be energized in the open position, it must carry a warning label. The PV system may have up to six disconnecting switches or circuit breakers for each system.
• Equipment disconnecting means (690.15): isolating devices or equipment disconnects for inverters, charge controllers, and similar equipment must be within the equipment, or within sight and within 10 ft of it, or have a lockable or remotely operated means as permitted.
• Service marking (230.70, 2026): where the PV disconnect is not located at the service disconnect, a plaque or directory at the service disconnect must show its location.

Wiring methods (690.31)

• Exposed in the array: single-conductor PV wire or USE-2 cable may be used exposed outdoors within the array, protected from physical damage and supported.
• Inside buildings: where DC circuits of a PV system run inside a building and exceed 30 V or 8 A, they must be in metal raceways, Type MC cable with a metal sheath, or metal enclosures, from the point of penetration of the building surface to the first readily accessible disconnecting means.
• Markings: raceways, cable trays, and enclosures containing PV DC circuits must be marked "PHOTOVOLTAIC POWER SOURCE" or "SOLAR PV DC CIRCUIT" at intervals not exceeding 10 ft, and on each section separated by walls or barriers.
• Identification: PV DC conductors are identified by polarity at all termination, connection, and splice points, and only a solidly grounded conductor may be white or gray.

Grounding (690.41 to 690.47)

• Most modern PV arrays are functionally grounded through the inverter rather than solidly grounded.
• Equipment grounding (690.43): exposed metal parts, module frames, and racking must be connected to an EGC, using devices listed for bonding module frames where used. EGCs for PV circuits are sized from Table 250.122 using the OCPD rating; where no OCPD is used, an assumed OCPD rated per 690.9(B) is used (690.45).
• Grounding electrode (690.47): a building with PV must have a grounding electrode system per Article 250; the 2026 NEC removed the former Article 250 wording about additional array electrodes from 690.47(B).

Interconnection

Connecting the PV inverter output to the premises wiring is covered by Article 705: supply-side connections and load-side connections, including the 120% busbar rule. Section 20.2 of this guide covers those rules.