Wire Management is a vital part of every residential solar photovoltaic (PV) Installation. It is the foundation of efficiency, good production, and safe operation of the array. PV systems are complex, the environment is harsh, and installation can be difficult. As a result, getting wire management right is not always easy, but with quality equipment and best practices you can ensure your wire management will last as long as the rest of the array.
A typical 60-cell module has 6.5 feet of DC leads and two connectors. A typical optimizer has seven feet of leads and four connectors. Multiply that across a basic 30-moudle residential array and that’s over 400 feet of cable and 240 connectors. These pre-installed leads need to work in any wire routing scenario, so much of that length is slack that must be organized and secured. Additionally, these 400 feet of cable and connections are installed on a rooftop that amplifies temperatures, rising above 100°F in the summer and dropping well below freezing in the winter. This temperature swing subjects the wires to significant thermal expansion and contraction.
These extreme conditions are often present during the installation. Working in sweltering heat or freezing cold, installers can complete about half of the wire management before the modules are set in place. For the other half, they must reach under the panels, make the remaining connections, and secure the wires with limited working clearance and limited visibility. This is never fun and can even be hazardous.
All these factors can create complications before you even get to the installation. The nature of the equipment, the environment, and the installation sequence come together to create a perfect storm of challenges. So, let’s talk about how to navigate that storm with the right combination installation practices and components.
There are many wire management techniques, but the end goal is always the same—to preserve life and property by securing the wires to prevent conductor damage that would lead to an electrical fault.
A few key tips:
- Keep it Neat: NEC 110.12 says, “Electrical equipment shall be installed in a neat and workmanlike manner”. Besides maintaining code compliance, neat and orderly wire management helps ensure everywhere is secured, reassures inspectors to sign off on the inspections, and helps future maintenance operations.
- Sharp Edges: Cutting mounting rails to length can leave sharp edges. Take care to route wires away from these areas and—even if the edge is not sharp—don’t pull wires tight around the edge.
- Roof Contact: Perhaps most importantly, keep the wires off the roof. The surface is abrasive. If wires contact the roof, wind and vibrations can wear right through the insulation over time, resulting in an electrical fault.
- Tension: PV Wires are subject to huge temperature swings. They will expand and contract significantly—much more than one might expect. A continuous support method doesn’t require tension. Tension needs to be balanced to keep wires off the roof, while also allowing room to contract without pulling out of clips or tight around an edge. Getting this right is more of an art than a science, but a good rule of thumb is to always have a little bit of a bow in the wire. If it’s sagging too far, opt for more attachment points over more tension.
- Methodology: Whenever possible, use continuous support. These systems “automatically” prevent contact with the roof and sharp edges and remove the need to carefully balance tension between attachments.
Now that you understand the primary goals of wire management, it’s time to select the right components.
There are two primary “types” or “methodologies of PV Wire Management- Interval Support and Continuous Support. The components required for each of these are different, but regardless of the methodology you choose, always select components from trusted brands that are specifically designed for the harsh conditions on a solar array.
1. Components for Interval Support
Interval Support is based on securing cables with clips or ties every few feet. It is highly adaptable, working with every type of racking system from ground mount to rooftop, rail to rail-less and is the most common method in the industry.
- Plastic ties – I know a lot of you reading this article use zip ties. They’re simple, versatile, and inexpensive. But during my time in the industry, I’ve seen many cable or zip ties fail. While they can help in a pinch, there are two important things you should understand if you are going to purchase ties:
- UV-rated has a very broad definition and does not denote a specific life expectancy. The UV resistance of the materials used varies widely. Never buy a tie that is just labeled UV-rated.
Solar-rated ties from trusted brands will last longer than comparable UV-rated ties, but even they are not a lifetime solution. In fact, Solar-rated ties aren’t rated or warrantied for a specific lifespan. Their manufacturers consider them to be a maintenance item that will need to be replaced at least once during the serviceable life of the array.
- Metal cable ties are an alternative to plastic ties, but their sharp edges introduce risk of conductor damage, especially when wires are tensioned.
- Wire Clips have the longest life span. Look for products with smoothed, rounded, “coined” edges that will not damage the wire it is securing. Be sure to get clips that are sized to hold the right type and quantity of wires. Consider a combination of module frame edge clips and rail-clips and be prepared with enough clips that you can place them close together to reduce sagging and tension on the wire.
2. Components for Continuous Support
While Interval Support is based on spanning the wires between attachments points, the second type of wire management, Continuous Support, is based on securing cables by supporting their entire length. The wire is laid into place without tension and allowed to freely expand and contract with thermal cycling. This reduces stress and strain on the wire, eliminates the risk of a wire sagging or popping loose and becoming damaged, and it simplifies the installation process.
Continuous Support wire management is common outside of the array, in the form of conduit and cable trays. Inside the array, open channel mounting rails offer only a partial solution, as they still require clips or ties and can damage wires and connectors with fasteners protruding into the channel and ponding water.
There just hasn’t been a good Continuous Support device sized to fit in the slim space under a typical rooftop array and that’s why Unirac developed SolarTray.
It’s a Continuous Support Wire Management System that works with any rail with a top mounting channel. It supports East-West and North-South wire runs and also grips and holds inbound cables, making it the only Continuous Support PV Wire Management System that handles every wire run in the array without the use of a single clip or tie. Per module, it costs about the same as using good quality wire clips, but it installs faster and provides maintenance-free wire management for the life of the array. It’s the ultimate solution for the perfect storm of challenges installers face with wire management.
If you aren’t already using Solartray, you can request a free sample by filling out the form below. It’s part of Unirac’s commitment to Better Solar Starts Here. Let us help you spread solar to more people and, hopefully, make your job a little bit easier in the process.