In “Code Corner” (HP158), some of the changes to the 2014 National Electrical Code were highlighted. Part two continues this discussion.
Many of the new sections in Article 690, Part IV, “Wiring Methods,” were moved from other locations. There also are some new requirements. Previously, DC conductors had to be installed in raceways on arrays with a maximum voltage greater than 30 V that were installed in “readily accessible locations” (e.g., ground mounts). Now, Section 690.31(A) allows them to be guarded—“covered, shielded, fenced, enclosed, or otherwise protected…[which] removes the likelihood of approach or contact by persons or objects to a point of danger.” This means that screening, some wire-management systems, or even lattice-wrapping the exposed sides and back of an array may be acceptable, rather than having to use a raceway or render the array inaccessible (such as with a fence, or by making it high enough to require a ladder). The authority having jurisdiction (AHJ) will have the final word on acceptability of individual strategies.
Section 690.31(B) now requires that DC PV circuits (both source and output) be separated by a partition from any other conductors when they share a raceway, junction box, or “similar fitting.” A gutter box installed below an inverter and the inverter’s external AC and DC disconnects must have a partition between AC and DC wiring; it will not be permissible for them to cross over each other.
Cable tray is a popular wire-management device for all sizes of systems, but the requirements in other sections of the Code about its use with smaller conductors, such as those used for PV source circuits, were confusing. Section 690.31(C)(2) now explicitly allows use of cable tray for PV-source and output circuits if they are listed PV wire, even when it’s not marked for use with cable tray. The enhanced durability of PV wire led to this allowance, along with the realization that, especially on commercial rooftop systems where thermal movement and expansion and contraction can wreak havoc, conduit may not always be the best installation method for conductors. The conductors in cable tray must be supported at least every 12 inches, and secured at least every 4.5 feet.
The increased use of microinverters also has led to new Code wiring additions. Section 690.31(D) permits TC-ER and USE-2 cable to be installed on utility-interactive inverters in locations that are not readily accessible—for example, as the AC output conductors connected to microinverters behind PV modules. This section also specifies that there must be an equipment grounding conductor in the cable, and requires the cable be supported at least every 6 feet.
Continuing efforts to harmonize language with the International Fire Code, Section 690.31(G) extends requirements for conductors inside a building to those on a building. The label, “Warning: Photovoltaic Power Source,” must be applied on conduit (exposed raceways) at least every 10 feet, and on cable trays and junction boxes on roofs or exterior walls. As with the rapid shutdown label requirement, this is more specific than 110.21 field applied hazard marking guidelines, specifying reflective, white capital letters, at least 3/8 inch tall, and on a red background.
Ungrounded PV systems are becoming increasingly common, and additional wiring methods are now allowed in Section 690.35(D). Both metallic and nonmetallic jacketed, multiconductor cables are now allowed for PV source-circuits, along with cables that are buried, provided they are identified as appropriate for direct-burial. New language in 690.47(B) provides clarity by allowing the AC equipment grounding system to be used as the ground-fault detection reference for ungrounded systems, along with the allowance in 690.47(C)(3) that the conductor providing the bond to the AC equipment grounding system be sized as an equipment-grounding conductor per Table 250.122.
Deleted in the 2011 edition of the NEC, Section 690.47(D), which requires additional auxiliary electrodes for array grounding, is back in 2014. This is a contentious issue, with experts questioning whether the additional grounding electrodes are being mandated as lightning protection; if so, whether this requirement should fall under NEC jurisdiction; and whether there are legitimate merits in requiring this for rooftop systems in addition to ground- and pole-mounted systems, or at all. Expect this section to be reexamined in future code cycles as well. See “Additional Electrodes for Array Grounding,” in SolarPro magazine 1.1 for more information. Note that many experts agree that any electrode added to a building should be bonded to the existing grounding electrode system. This is not a requirement for auxiliary electrodes (see 250.54), but can lead to dangerous differences in potential in the event of a surge or lightning strike.