Section 200.6(A) dictates that grounded current-carrying conductors smaller than 6 AWG “shall be identified by a continuous white or gray outer finish or by three continuous white stripes on other than green insulation along its entire length.” An exception to 200.6(A)(2) allows PV source conductors to be installed and marked at their terminations. The use of white tape on black wire, for example, can identify a PV source conductor as grounded.
When describing and calling out conductors, it is more appropriate to refer to nongrounded current-carrying conductors and grounded current-carrying conductors. The former is typically the positive conductor, and the latter typically the negative. This is more descriptive and identifies the conductor’s role in the circuit to qualified personnel. Under this nomenclature, color coding is also clarified.
The nongrounded current-carrying conductor may be any color other than white, gray, green, or green with yellow stripes. Typically, this conductor is red, which is acceptable per the NEC and stands out to a technician servicing the system. When a positively grounded PV system is employed, it may be in the installer’s best interest to use both proper color coding (such as having a white positive conductor and black or red negative conductors) and additional labeling to identify the system as positively grounded.
Readily accessible conductors. NEC Section 690.31(B) allows for the installation of unprotected current-carrying conductors in PV systems. In the 2008 and 2011 NEC, however, 690.31(A) states, “Where photovoltaic source and output circuits operating at maximum system voltages greater than 30 volts are installed in readily accessible locations, circuit conductors shall be installed in a raceway.”
This requirement is problematic for ground-mounted or other PV arrays that are considered “readily accessible” per NEC Article 100, and those that use modules with quick-connect cables attached to the junction boxes, since these modules don’t have a method for conduit attachment, making article compliance difficult to achieve. The installer is left with the dilemma of how to best install the system and comply with the NEC. For ground-mounted systems, an easy answer is to build a fence to keep the system isolated. Another method to render the wiring inaccessible is to create a wiring chase that integrates with the racking system. Work closely with the AHJ to determine what is acceptable.
Section 690.31(E), which first appeared in the 2005 NEC, allows DC conductors from the PV array to run through a structure before being terminated at a readily accessible disconnect, as long as the conductors are located in a metallic raceway. The 2008 NEC generally accepted that metallic raceways include conduit such as EMT and flexible metallic conduit, but not metal-clad cable, which is technically a cable assembly. The section also includes language that refers specifically to grid-tied inverters; depending on your AHJ’s interpretation, the method outlined in Section 690.31(E) may not be acceptable for off-grid installations. For systems installed based on the 2011 NEC, see the 2011 NEC Section 690.31(E) sidebar for an outline of the new requirements.
Point of connection. One of the requirements in the 2008 and 2011 NEC makes a violation out of a common practice allowed in the 2005 Code. Section 690.64(B)—or Section 705.12(D) in the 2011 NEC—now requires that the inverter output connection for grid-tied systems be made at the opposite end of the bus bar from the main circuit breaker location, unless the sum of these two breakers is less than the bus bar rating. Per this language, in typical residential installations, the inverter connection must be located at the opposite end of the panel from the main breaker, with the PV breaker labeled, “Do not relocate.”
Fine-stranded cables. Section 690.31(F), added in the 2008 NEC, specifically requires that fine-stranded cables only be used with terminals or lugs identified and listed for such use. In battery-based systems, it is common to use fine-stranded cables for the battery interconnects and the battery-to-inverter connection.
When fine-stranded cables are used in connections not specifically listed for that use, the conductors will expand and contract within the connection, eventually causing a high-resistance connection and, possibly, leading to failure.