For aesthetic reasons, more customers and installers are turning to flush-mount, pitched rooftop solar systems that are increasingly getting closer to the roof. One thing sometimes overlooked when designing the most attractive system is just how to manage all the wires underneath.
There isn’t a blanket method for proper wire management on these projects. How to secure PV cables depends on the racking system, modules and the type of roof covering on the building. And don’t forget the difficulty in running hundreds of feet of wire on an inclined surface.
“You’re asking [installers] to try and route wires in a 4- to 6-in. space and then use clips that are the size of a quarter and install them while routing wire safely — and it’s probably 130°F on the roof,” said Nick Korth, product marketing manager for HellermannTyton. “There’s a whole bunch of factors that create an environment where it’s easy to cut corners and it’s very easy to do it wrong or do it cheap.”
Securing cables correctly the first time will save installers from spending money on a truck roll just to replace some broken zip ties.
Wire management solutions
Most solar racking and mounting manufacturers carry products specific to wire management, and companies like HellermannTyton and Burndy (which carries the Wiley line of products) have a range of clips and ties for securing solar cables. But this specialized equipment is often overlooked for a cheaper alternative.
“I think what installers may not know is that there is a purpose-built product for every application, and sometimes they don’t look hard enough for the solution,” said Susan Stark, senior manager of training at IronRidge. “[Installers] started making their own [wire solutions], and making their own is a highly fraught experience because they don’t totally understand the amount of movement that this is going to have over time.”
The common solution for securing wire on a flush-mounted array is simple plastic zip ties bought from any home improvement store. These cable ties are inexpensive and made of a low-level composite that is neither solar-rated nor UL-certified to withstand the vast temperature changes underneath a residential solar system over its operating lifespan.
Technicians will return to arrays to find broken zip ties and wires hanging loose and touching the roof, creating potential electrical hazards and system faults. Only plastic ties that are tested for prolonged exposure to sunlight, extreme temperature changes and vibrations should be used on solar projects. HellermannTyton alone carries nylon Solar Ties, edge clips and metal clips that snap onto module frames and rails.
Whether to use metal clips or plastic cable ties depends on site conditions and installer preference. Metal clips are stronger and have a longer lifespan, but they can have sharper edges that cut into components if secured incorrectly, including into the PV wiring itself.
“At the end of the day, the thing I go back to is labor,” Korth said. “How consistent do you think your installers are going to be installing metal clips, and are they going to cut corners?”
Certain rail-based solar mounts are designed to work with accessory wire clamps. Then there are clip-free cabling solutions like Unirac’s SOLARTRAY, a wiring channel that clicks onto the racking rail and runs the length of a module, supporting the entire length of cable.
Securing the wiring
Wiring is a task handled throughout the installation of a flush-mount array. On a 30-module residential solar project, installers can expect to be working with around 400 ft of cable and more than 200 electrical connection points.
“The sheer number is just something that I don’t think installers quite realize,” said Brady Schimpf, marketer and product developer for Unirac. Schimpf wrote the white paper “Wire Management Best Practices” for the mounting company that was published in May.
Preplanning how to keep all the PV wiring secured to the junction-box edge of the module allows for easy maintenance access in the future. Wires from junction boxes can be attached to the panel frame with cable ties or wire clips before laying down any modules. Homerun wires are attached to the racking system (if there is one) with cable ties or accessory wire clamps.
When split junction boxes are centered on a module, like in the case of half-cell panels, wires need to be led across the backsheet to the module frame to meet the planned route.
“You look at the number of modules you have, the layout of that array and decide how many source circuits (strings) are going to have to be in this array based on the inverter manufacturer’s guidance or the optimizer manufacturer’s guidance,” IronRidge’s Stark said.
Module-level power electronics are attached to the rail or module frame and both sets of cables can be inserted into module clips or ties — if there’s enough space. Managing the wires before laying the panels will save installers from trying to do attachments in that narrow space.
Cable management solutions like SnapNrack’s Universal Wire Clamp fasten to the channel on the company’s proprietary roof rail. The clamp can guide wiring at any angle under the array at multiple points on the rail. Unirac’s SOLARTRAY clicks onto one side of the rail channel system. Cable is fed into the tray’s slot. It was designed to accept excess wiring, making the rail the route for PV cable.
Cable ties can be used on either the rail or the module frame. Ties are attached to module frames using additional fasteners on the lip or guiding holes in the frame. HellermannTyton’s Korth recommended not running cable ties through the guiding holes though, as that can cause breaks.
While low-grade zip ties are a problem, improper installation practices with any wire management solution can also be detrimental. If an installer is using plastic or metal ties, they can’t be pulled too tightly around the wire, otherwise the cable will expand in the heat and cause the tie to break. If using clips or ties for routing wires, the cable can’t be so slack that it’s touching the roof, nor can it be too tight like a guitar string.
The entire system, including the cable, will expand and contract between hot and cold temperatures. Giving cables just enough space to do so without forcing the wiring out of its clips or ties is key.
“Unless you’ve actually installed and done [wire management] for a while, it’s difficult because it is so much of an art,” Unirac’s Schimpf said. “It’s hard to fully wrap your head around sometimes.”
Solar installers should set down that cheap bag of plastic zip ties and consult mounting companies or wire management manufacturers to ensure their arrays don’t have future cable issues.