690
Solar Photovoltaic (PV) Systems
If you install solar panels, Article 690 is your bible. It covers every aspect of PV system wiring from the modules on the roof to the point of connection with the building electrical system. Section 690.7 sets maximum voltage limits — 600V DC for residential one- and two-family dwellings and 1,000V DC for commercial buildings. These maximums are based on the lowest expected ambient temperature at the site, not standard test conditions, because cold temperatures increase PV open-circuit voltage. Section 690.8 requires a double 125-percent calculation for circuit sizing: first you multiply the module short-circuit current (Isc) by 1.25 to account for irradiance above standard test conditions, then you multiply again by 1.25 for continuous load treatment, giving an overall factor of 1.56 times Isc for minimum conductor ampacity. Section 690.9 requires overcurrent protection devices rated at least 1.25 times Isc, and they must be listed for PV applications on the DC side. Section 690.11 mandates DC arc-fault protection for systems operating at 80V DC or greater — this detects dangerous arcing from damaged conductors or loose connections before a fire starts. Section 690.12 is the rapid shutdown requirement: within 30 seconds of initiation, controlled conductors inside the array boundary must drop to 80V or less, and conductors outside the boundary must drop below 30V. The 2023 NEC added an exception for non-enclosed detached structures like carports and solar trellises. Section 690.31 covers wiring methods, requiring PV wire or USE-2 for exposed module interconnections.
When You Need This
- Installing a residential rooftop solar system and need to size conductors, overcurrent devices, and the rapid shutdown system
- Designing a commercial solar installation and calculating maximum system voltage based on lowest expected temperature
- Determining arc-fault protection requirements for a new PV array
- Answering exam questions about solar — Article 690 is appearing with increasing frequency on journeyman and master exams
- Planning a solar carport installation and need to determine whether rapid shutdown applies (the 2023 exemption may apply)
Key Points
Common Mistakes
Using standard test conditions (STC) to calculate maximum voltage instead of the lowest expected ambient temperature — cold increases Voc significantly
Applying only one 125% factor for conductor sizing instead of the double 125% (1.56x) required by 690.8
Using standard household circuit breakers on the DC side — PV DC overcurrent devices must be specifically listed for PV applications
Omitting the rapid shutdown system on a residential rooftop installation — 690.12 applies to all building-mounted PV arrays
Assuming arc-fault protection is optional — it is mandatory for any PV system at or above 80V DC per 690.11
Running standard NM cable (Romex) for exposed PV wiring on a roof — only PV wire, USE-2, or approved wiring methods per 690.31 are permitted
Exam Tip
The double 125% factor is the most tested concept from Article 690. If the exam gives you a module Isc of 10A, the minimum conductor ampacity is 10 x 1.25 x 1.25 = 15.63A. The OCPD must be rated at least 10 x 1.25 = 12.5A. Also know the rapid shutdown voltage limits: 80V inside the array boundary, 30V outside, within 30 seconds.
Frequently Asked Questions
The first 1.25 factor (690.8(A)) accounts for the fact that real-world solar irradiance can exceed the standard test conditions used to rate the modules — on a clear cold day, modules can produce more current than their rated Isc. The second 1.25 factor (690.8(B)) treats the PV output as a continuous load per standard NEC rules. Combined, this gives a 1.56x multiplier on Isc for minimum conductor ampacity.
Rapid shutdown (690.12) is a safety system that de-energizes the PV array conductors quickly — within 30 seconds — when initiated. It exists primarily to protect firefighters who need to work on or near a roof with solar panels. Without rapid shutdown, the DC conductors between the panels remain energized at potentially lethal voltages whenever the sun is shining, even if the main service is disconnected.
Yes, if the system operates at 80V DC or greater between any two conductors, which virtually all grid-tied residential systems do. DC arc-fault circuit interrupters (AFCIs) are built into most modern string inverters and module-level power electronics (MLPEs), so this requirement is typically met by the inverter or optimizer hardware.
Related Code Sections
This is an educational summary, not the official code text. The NEC® is a registered trademark and copyright © National Fire Protection Association (NFPA). The CEC is copyright © CSA Group. For official code text, visit nfpa.org or csagroup.org. SparkShift is not affiliated with NFPA or CSA Group.