This article outlines procedures for means of providing safe access, pathways and areas considered appropriate for egress to and from photovoltaic (PV) systems. It contains techniques for inspecting the location of PV direct current (DC) circuit conductors installed on or in buildings or structures. This procedure includes inspecting the grounding methods for design and installation of roof-mounted PV systems per National Electrical Code (NEC) requirements. This PV-system inspection procedure is not the only approved method. It is only a guideline.
Ground-mounted photovoltaic systems
1. Exterior-mounted DC conduits. Wiring systems and raceways for PV circuits shall be located as close as possible to the ridge, hip or valley and, from the hip or valley, as directly as possible to an outside wall to reduce trip hazards and maximize ventilation opportunities. It is recommended to also use these requirements for alternating-current-routed conduits.
2. Conduit runs between sub-arrays and DC combiner boxes shall use design guidelines that minimize the total amount of conduit by taking the shortest path from the array to the DC combiner box.
3. DC combiner boxes shall be located so that conduit runs are minimized in the pathways between arrays.
4. The DC wiring shall be run in metallic conduit or raceways when located within enclosed spaces in a building and shall be run as follows:
a. When run perpendicular or parallel to load-bearing members, a minimum 10-inch space below roof decking or sheathing shall be maintained.
b. Where flexible metal conduit or metal clad cable containing PV circuit conductors is installed across ceilings or floor joists, the raceway or cable shall be protected by guard strips.
Markings, signage and other requirements
1. Markings and signage shall comply with the requirements listed in Section I (click here for more).
2. Setbacks. Special setback requirements do not apply to ground-mounted, freestanding PV arrays. Note: The zoning regulations of the jurisdiction will regulate setbacks between buildings, accessory structures (ground-mounted PV arrays may be included) and property lines.
3. Clearances. A clear area of 10 feet around ground-mounted PV installations shall be provided.
4. Noncombustible Base. A gravel base or other noncombustible base acceptable to the electrical inspector and fire code official (authorities) shall be installed and maintained under and around the installation.
5. Protection. Fencing, skirting or other suitable security barrier shall be installed when required by the authorities. Note: security barriers are intended to protect individuals and animals from contact with energized conductors or other components.
6. Fire Sprinkler Protection. Fire sprinkler protection is not required for ground-mounted PV installations.
Grounding PV modules and mounting hardware
These issues should be addressed when evaluating the grounding system for PV installations because there may be conflicts between the requirements of the manufacturer’s installation instructions and the NEC.
Section 690.43(A) in the 2011 NEC is very clear in its intent to require appropriate grounding of modules and hardware. It states, “Exposed non-current carrying metal parts of PV module frames, electrical equipment, and conductor enclosures shall be grounded in accordance with 250.134 or 250.136(A), regardless of voltage.”
Section 690.43(B) covers the equipment that can be grounded per 690.43(C) when the structure is used as part of the equipment-grounding conductor (EGC) scheme. I recommend a careful review of 690.43(D) through (F). Although this method is available, it is seldom used in the field due to difficulties establishing and maintaining a reliable, low-impedance grounding connection between electrical devices and their associated mounting rack and other hardware. I have found that it is an industry practice to install a properly sized EGC rather than to use other techniques recognized by the NEC.
The task of understanding the NEC grounding requirements continues with a portion of 250.136(A), which states: “Electrical equipment secured to and in electrical contact with a metal rack or structure provided for its support and connected to an equipment grounding conductor by one of the means indicated in 250.134.” The structural metal frame of a building shall not be used as the required EGC for AC equipment.
Article 250.118 outlines 14 different types of recognized EGC schemes that can be used to ground and bond the modules and associated hardware. Indeed, it is possible to use the structure as an EGC, if done so in compliance with 110.3(B) and 690.43(C). When inspecting the grounding of PV systems, authorities should follow the requirements outlined in Part V of Article 690 of the 2011 NEC.
STALLCUP is the CEO of Grayboy Inc., which develops and authors publications for the electrical industry and specializes in classroom training on the National Electrical Code and other standards, including those from OSHA. Contact him at 817.581.2206.