Best practices in solar PV wire management for the skilled installer

Installation comparison: PV mounting on rails on the left and PV mounting without rails on the right.

One of the most important aspects of any metal roof solar PV installation is wire management, but even seasoned professionals can find this task confusing. There are countless things to follow. You will need to position the conductors so that they connect correctly when the modules are installed, keep all wires off the roof, provide jumpers to the home run and to the inverter, and stay organized. If you have a large-scale job, this process becomes more and more complex.

We’ve got some best practices to share on wire management planning and mechanics to make your setup easy. Today we’ll show you why it’s important to:

  • Prepare modules before installing.
  • Design your string and module layout to minimize installation time.
  • Select the wire management method that best suits your project.

What are the ways to mount solar PV on your metal roofing?

There are two ways to attach solar panels to your metal roof:

Solar PV installation close-up: mounting without rails vs. mounting on rails

Rail and railless assembly share similarities when it comes to wire management best practices – including careful planning before going on the roof. When it comes to railless solutions, planning is essential. In addition, the preparation of the module forms the basis for the most efficient installation.

Why is module preparation important?

Module preparation on the ground minimizes your time on the roof. The result is a smooth installation and less net working time.

The cable guides on the bottom of the modules are long and can get lost under the modules during installation. It can be difficult, time consuming and stressful to turn over large modules or reach under them to find the ends of the conductors.

Preparing your modules on the ground makes it easy to coil up the excess wiring to keep the wires off the roof. Now is a good time to place the conductor ends exactly where you need them so that you can easily connect them to adjacent modules or to jumpers at the end of the string. You can prepare all your modules first or split your crew (some members prepare modules on the ground and others install them on the roof at the same time).

Why should you create a wire management plan?

Many installers are eager to bring the equipment and hardware directly to the roof. Unless you have a simple, small-scale residential job, this rushed approach may cost you more time and headaches than you think. The challenge is figuring out the best way to get all your wiring to the inverter, and the simplest installations are carefully planned on the ground.

Don’t skip this important step! Planning your project will ultimately save you time, money and hassle.

Strategic String Design

It is best practice to think about your string design to optimize the positions of the jumpers and minimize their lengths, making routing to the home run easy. Map your strings so that each has the conductor ends as close to the perimeter of your array as possible. When done professionally, you won’t be bothered by conductor ends in the middle of the array, leaving you with hard-to-reach cable wires. You can simply go to the outside of the array and simply connect the leads to jumpers leading to the home run.

As with any new process, calculating your string design layout gets easier the more you do it, and you’ll reap the benefits of a clutter-free, smoother, and faster installation once you’re on the roof.

For example, imagine you have eight columns of modules in an array. If you choose to use strings of 16 modules, each string will run the length of one row and back to the other, bringing the string ends to the perimeter of the array. Due to possible obstacles, you may still have a few guide ends that don’t reach the perimeter. But the closer your design brings the ends to the edge of the array, the more you avoid running long jumpers deep into the array and securing them off the roof.

Whether all your string ends are on the perimeter or you have a few more in the middle of the array, your next step is to lead them to the home run. Let’s look at two wire management layout options to help organize your project: the “direct” method and the “trunk” method. Each comes with pros and cons. The size of your project and your professional preferences play an important role in the method you choose.

The direct method

For commercial projects, general wiring design is the direct method. In this design, you simply attach jumpers to the end of each string and then run them the length of the panels to the home run. This method seems simple enough, but it generally requires a lot of wiring to get to the home run, as your strings can end in the middle of your array — leaving you with a lot of long wires to stay off the roof.

If you are using rails, you can pre-tie the wires to the rails, but this process takes a lot of work. For railless designs, clip the jumper wires to the module frames or railless mounting fittings.

Looking for railless solutions with built-in wire management slots? look at the PVKIT.

The direct method allows you to refer to your wire management plan and lay down your jumpers before installing the module. On smaller jobs, you may decide to lay down your jumper wires as the module installation progresses and snap them in while you’re at it.

The direct method is a good choice for many residential installations because it takes fewer total strings (two or three) to connect to the home run, so you have less jumper wires to manage. But when it comes to larger projects, the direct method requires more installation time and tends to get disorganized.

Instant method snapshot

  • Wires run “directly” to the home run
  • Can be installed before module installation
  • Can be installed on the fly
  • More labor intensive
  • Less cost effective
  • Gets harder as the array scales

Another alternative that is better suited for larger, more complex solar PV systems is the trunk method.

The Trunk Method

A “trunk” is a wire management tray or conduit in which jumper wires are bundled and routed to the home run. The trunk method requires planning in advance where the conductor ends of the strings will be attached to the jumpers and where the wire management trays or conduit will go. This design saves the time and effort of having to snap the jumpers onto individual module frames or rails (as required in the direct method). However, the trunk method requires some preliminary work as all your jumpers must be in place before installing the modules.

Many consider this method to be more organized and easier to manage, but the size of your system makes a difference. When you compare the trunk method to the direct method, the two approaches can vary greatly in cost. Ultimately, you can save time and money by using specific wiring designs, such as the trunk method, on large projects.

Stem method snapshot

  • More hands-on time and pre-planning module installation to determine where cables go
  • The wiring is physically done before the modules are installed
  • Use of cable trays (preferred method) or cable tray
  • Simplifies cable routing
  • Less installation time

Interested in learning more about the trunk method and other approaches to wire management when installing larger solar systems?

Ideas to hold on to

Efficient PV array installation relies on proper wire management organization. It’s easy to get caught up in the process if you’re not sure where to start. Today we discussed the best practices for planning the electrical design of your array:

  • Advanced module preparation
  • String design and layout for faster installations
  • Project Specific Wire Management Methods

Looking for guidance in finding the right product for your application and determining the overall layout? Let our solar calculator do the work for you!

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