IN THIS CHAPTER

Supplying the proper structural support and keeping things dry

Making sure your conductors are rated properly, grounded, and more

Giving your system some space and attaching the right labels to it

When installing PV systems, you have multiple options for both the mechanical and electrical portions of the installation. Yet regardless of your chosen method, you must keep in mind all the appropriate codes to ensure a safe and secure installation.

• On the structural side of installations (which I describe in Chapter 16), the International Building Code (IBC) is the governing document. It’s the basis for local building codes, but it isn’t the only structure-related set of regulations you must deal with; the local jurisdiction will likely have additional structural guidelines that you must follow.
• On the electrical side, the National Electrical Code^® (NEC^®) is the primary document that will be referenced by the local authority having jurisdiction (AHJ). I go through many (but not all) of the NEC^® sections that apply to the electrical part of PV installations in Chapter 17. You, the installer, must be familiar with these Code sections and install your systems to meet NEC^® requirements.

This chapter is a quick reference to the most commonly encountered problem areas as they relate to complying with the NEC^® and the IBC. By avoiding these mistakes from the beginning, you can save yourself a lot of time (because you don’t have to waste time fixing something you should’ve gotten right the first time) and squeeze in more clients as a result.

Whenever you have a question as to what requirements your system will be held to, check in with the local building department for clarification.

Providing Proper Working Clearance

When you install different pieces of electrical equipment, you need to make sure each component has the proper amount of working clearance around it. Article 110.26 of the NEC^® defines the general requirements for proper working clearances. The basic idea is that someone should be able to walk up to a piece of electrical equipment and have proper access to service the item. In addition, many inverter manufacturers have a minimum clearance requirement to help keep cool air flowing around the inverter.

The requirements for working clearance include a minimum width, a minimum height, and a minimum depth that must be kept clear for access. Generally, electrical components need to have at least 30 inches of width, no less than 6½ feet of height (with some exceptions for residential installations), and 3 feet of depth. (Note: Some of the requirements vary based on the operating voltages of the equipment, so be sure to check the NEC^® to figure out exactly what’s required for your installation.) You can imagine this space as a cube floating in front of your equipment that must be kept clear at all times.

If you install the equipment in a location that your client may use as a storage space, mark the area to eliminate the potential for clutter. It can be very tempting to use “unused” space for storage, but when the day comes that someone (usually you) needs to access any of the system components, you don’t want to spend half the day clearing the space of the client’s junk just to get to the equipment (especially in an emergency situation).

Supplying the Right Structural Support

No matter how you mount a PV array — on a roof, on the ground, or on a pole — all the components need correct support. To determine exactly what kind of support is necessary, always refer to both the manufacturer instructions that come with the PV modules and those that come with the racking system. These two documents note the basic requirements for installing an array correctly.

• Module manufacturers help you make sure the module frame is properly supported by the racking system. These requirements are independent of the racking type and ensure the modules’ weight is distributed properly.
• Racking manufacturers point out the maximum distance you can have between supports for the racking system; they also tell you what length of rail can be run past the last support (the cantilever) and the maximum allowable length between supports along the rail length.

When you mount an array on a roof, you must review the roof truss or rafter system to make sure the roof is capable of handling the new loads imposed on it by the array. (Chapter 16 walks you through the major considerations for this analysis.) As for ground and top-of-pole mounts, you must examine the foundation that will hold the array down for the soil conditions you’ll install it in.

Keeping Water out of Buildings with Flashing

No surprise here, but people are generally unhappy with water on their ceilings. This fact is all the more reason to keep water out of the buildings you work on. Water leaks are a real concern for any installation located on the roof of a building, but they’re also a consideration for installations where wiring and conduit are brought from the outside to the interior of the building. Always use appropriate sealants for the building material you’re penetrating.

For roof-mounted PV systems, use flashing to create a watertight connection between the racking and the roof. Flashing is a term used to describe a mechanical device that’s installed in conjunction with a roofing material to keep water out of roof penetrations (I describe flashing in more detail in Chapter 16). If you take a look at your roof, you’ll see flashings on all the plumbing vents coming out of your house.

Ensuring All Conductors Have the Necessary Ratings

PV systems offer the challenge of installing multiple conductor (wire) types in multiple environments. To meet this challenge, you must make sure all the conductors have the right ratings. For the PV source circuits, for example, you must use either underground service entrance (USE-2) wire or the relatively new PV cable. These conductors aren’t appropriate to run inside buildings, though, so you have to transition to a building-safe conductor, such as moisture- and heat-resistant thermoplastic (THWN), when running wires inside your client’s home or business.

For the building wire, I highly recommend you only buy the cable that’s marked THWN-2. The -2 in the name indicates that this conductor is rated at 90 degrees Celsius in both wet and dry locations. When ordering the wire, make sure to specify THWN-2; this way you know that, regardless of the conductor’s location, it’ll have the proper temperature and moisture ratings (although conduit is still required). See Chapter 10 for details on several different types of conductors.

Managing the Conductors on Modules

No matter where the modules are installed (on a rooftop or on the ground), conductors must be properly supported all the way to the junction box or combiner box. If they’re not, they may become damaged and eventually fail.

When PV module manufacturers added quick-connect plugs on the backs of their modules, they eliminated a lot of the labor required to connect modules in series. With quick-connect plugs, all you have to do is plug one module into the next one, and the connection is made.

What the manufacturers also did was introduce a new challenge for PV system installers to overcome. Before, all the conductors were nicely contained inside conduit; now that conduit isn’t necessary (or easily accommodated because there are no longer places to terminate conduit), installers have to secure the conductors between the modules. To do this, you must neatly tuck any excess wire along the module frames and racking structure. Fortunately, specially designed cable clips that attach to the module frame and hold onto one or two PV source circuit conductors are available. You can also use plastic or stainless steel wire ties to hold the conductors to the racking system if you desire.

Using plastic ties often seems like an attractive and easy option, but remember that PV modules will be out in the environment for a very long time and that plastic degrades. By using wire cable clips in combination with wire ties, you can keep the conductors in place and out of harm’s way.

See Chapter 17 for more information on managing conductors on modules.

Selecting the Correct Conduit

During the electrical portion of the installation, you must install some of the conductors inside conduit. For residential applications, you usually run the conductors from a rooftop array down through the building and to the electrical equipment within properly rated conduit. Article 690.31(E) in the NEC^® sets the requirements for such conduit runs. Be sure to verify the requirements based on the NEC^® version the local jurisdiction uses. (The NEC^® committee has made changes in this section in each of the last two Code cycles, with more changes to come in 2011.)

When you install conductors in other areas, such as in trenches for ground-mounted arrays or alongside the exterior of buildings for rooftop arrays, you need to make sure the conduit is rated for that location. PVC conduit can usually be installed in these locations, but be sure to verify the temperature limitations and sunlight-resistance qualities of the conduit for your installations.

Flip to Chapter 10 for a rundown of the different types of conduit and where they’re appropriate.

Locating the Disconnects

Disconnect locations are an important detail to keep in mind when designing and installing a PV system. The NEC^® requires that the disconnecting means for the conductors be grouped together and readily accessible. To satisfy this requirement, you must install disconnects for the PV circuits, battery circuits, and AC circuits used in the system. These disconnects must be grouped together and within sight of the inverter. Turn to Chapter 17 to find out about the most commonly used approaches for meeting the disconnecting requirements.

Grounding the Equipment

The subject of grounding is an ongoing source of frustration and friendly debate. But no matter your opinion, the NEC^® is fairly clear on at least a few grounding requirements, one of which is that all the exposed, non-current-carrying, metal parts of a PV system must be connected to ground. This requirement is telling you that you have to install what’s known as the equipment grounding conductor (EGC) for your racking system; PV modules; and all the disconnect boxes, charge controllers, and inverters.

Be sure to reference the module manufacturer’s and racking manufacturer’s installation instructions for specific grounding requirements. (Also, head to Chapter 17 for full coverage of the different methods for installing EGC.) Note: Some jurisdictions may only allow certain methods, so be sure to check in with the local inspector if you have questions.

Grounding the System

Although the NEC^® is perfectly clear about equipment grounding requirements (see the preceding section), its system grounding requirements most definitely aren’t. The NEC^® makes it clear that your PV system requires a connection to a grounding electrode (like a ground rod driven into the ground outside the building), but the exact methods and requirements for making this connection are less than straightforward.

Of all the system grounding requirements, the one that has you drive a supplementary grounding electrode for the array is the one that’s argued about the most. The more you read this requirement (found in Article 690.47 of the NEC^®), the less sense it makes. In short, you have to install a new grounding electrode (like a ground rod but separate from the existing grounding electrode) and connect the PV array racking system directly to this new electrode. This can become a difficult task because you don’t want to run the conductor from the array to the new grounding electrode through the house with the other conductors. For a ground- or pole-mounted array, adding this grounding electrode and connecting the array to it is no big deal because the array has clear access to the ground. As with a lot of the Code, exceptions to the rule exist, and if you can meet these exceptions, your life will be much easier. (I cover the most common methods for system grounding in Chapter 17.)

Because grounding is such a debated topic, I suggest that you talk through your strategies with the local inspector before you go down a path that he feels is inappropriate.

Labeling the System Properly

Of all the Code requirements that are violated, system labeling seems to be the most common one. I suggest you spend some time going through Articles 690 and 705 of the NEC^® to familiarize yourself with the label requirements as part of your design process. All too often, system labels are an afterthought, and they either don’t get installed or get installed incorrectly.

In Chapter 18, I outline the major system-labeling requirements for you. Most of the labels are “stock,” meaning you can buy a batch of labels that indicate the same information and can be used on any of your installations. On the other hand, some labels are custom for each job. One important example of such a label is the one that must go on the PV disconnecting means; this label requires you to calculate and list system-specific voltage and amperage levels.