Code Corner: Grounding & Bonding PV Systems

A bonding jumper
A bonding jumper connects two mounting rails to provide continuous grounding capability.
WEEB grounding washer
This WEEB grounding washer can be sandwiched between a module and its mounting rail. The protrusions bite into both, creating an approved ground path between them.
Grounding with a continuous copper wire
Traditionally, individual modules were grounded with a continuous copper wire.
Grounding lug
This grounding lug is commonly used to bond a grounding conductor to a mounting system.
A bonding jumper
WEEB grounding washer
Grounding with a continuous copper wire
Grounding lug

The equipment grounding section of the NEC’s Article 690 begins with references to Article 250 and the general requirements set there. Part VI of Article 250, Equipment Grounding and Equipment Grounding Conductors, outlines the general requirements, which are discussed here as well as the specific requirements in 690.43.

Starting in Section 250.110, the Code says about equipment-grounding requirements: “exposed normally non-current-carrying metal parts of fixed equipment supplied by or enclosing conductors or components likely to become energized shall be connected to an equipment-grounding conductor (EGC)…” when that equipment is exposed to any one of the conditions listed. PV arrays meet multiple conditions described in 250.110, which include being located in a wet environment and operating with any terminal with a potential to ground above 150 V, and so require connection to an EGC.

Section 250.110 helps establish the need for an EGC, but what is an EGC? Section 250.118 lists 14 different types of recognized EGC methods including using a conductor, certain conduit and tubing types, specific cable assemblies, and other metallic surfaces. This gives PV installers many choices in establishing and connecting equipment grounds. In PV installations, the most common EGC is either a stranded or solid copper conductor. Historically, installers have used lugs attached to all modules; conductors are then bonded to the lugs, thereby bonding all of the modules together. As I will discuss, recent changes to the equipment grounding section of 690 has opened the possibility of using other methods to create the required equipment ground connection.

Section 250.134, which is referenced in 690.43(A), provides two allowances for connecting to an EGC: 1) connecting to one of the EGCs permitted in 250.118; or 2) connecting to an EGC running with the circuit conductors. PV installations use the first option by connecting to a EGC as defined in 250.118. An exception in 250.134(B), which discusses DC circuits, allows the EGC to be run separately from the circuit conductors. However, Article 690 does not allow this method in PV circuits.

PV-Specific Equipment Grounding

Although the rules for properly grounding and bonding PV systems are covered in Part V of Article 690, this article contains numerous references to Article 250. Section 690.43, Equipment Grounding, covers the general requirements, listing six different sets of conditions the EGCs must comply with. The 2011 NEC breaks this section into multiple subsections. The first two subsections, 690.43(A) and (B), establish that equipment grounding is a fundamental requirement. These state that, regardless of system voltage, exposed noncurrent-carrying metal parts of PV modules and associated equipment must be grounded in accordance with 250.134 or 250.136(A), and are required in accordance with 250.110.

The language in 690.43(C) was new in 2008 and received a lot of updates in 2011. Interestingly enough, “or” appears multiple times, and has a big impact on the proper interpretation of the rules. This section identifies that a structure supporting a PV array can be used to establish the bond to the EGC. The first sentence of this section helps support the concept of using grounding washers to bond PV modules to the mounting structures, as long as the washers are listed and identified for that use. In the second sentence in 690.43(C), you really need to pay attention to the “or” since it has two allowances: the requirement that metallic mounting structures shall be identified as EGCs or the second that, in lieu of the mounting structure being identified as an EGC, that identified bonding jumpers can be used between the mounting sections and the mounting structure must be bonded to the grounding system. This is the method most installers use, due to the lack of mounting systems identified as EGCs.

Many would say this section causes more controversy than closure, but it does offer several options for a module-to-rack bond. One popular method is grounding washers. When installed properly, the barbed washers penetrate the module frames and the racking structure, establishing an electrical bond. However, some question if their listings are appropriate for this use. Their use satisfies most inspectors and thus they are widely used, but have very specific installation requirements to establish the proper bond.

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