A Do-It-Yourself Solar Array Wiring Primer

Do-It-Yourself Solar Array Wiring

In this article we will discuss the proper steps to wire a solar panel array to a combiner box for use in a solar electric system. For safety reasons, great care must be taken to ensure no wires are energized until all wiring is completed. This means that at least one series connection in each string of solar panels be left open until all other wiring is completed.  Wiring the solar panels is the last step in wiring a solar electric system, so make sure your transmission wires from the combiner box to the charge controller (off-grid system) or inverter (grid-tied system) are already connected before wiring the panels.

On the back of each panel there is either a Positive (+) and Negative (-) connection cable or a junction box with Positive (+) and Negative (-) connections indicated. Connection cables have solar industry standard water proof connectors, with the most common types being MC4, PV4, and T4. Junction boxes have terminals to connect user supplied wires. Connection cables or wire are used to connect panels to each other and to the combiner box, which is then wired to either a charge controller for off-grid systems, or an inverter for grid-tied systems. The combiner box is an outdoor rated enclosure, intended to be installed near the array, that serves as a junction point to tie together (combine) all wiring from the solar panels; Positive through breakers, and Negative through a negative bus bar. Strain relief wire fittings serve as wire pass-through-points for each pair of wires (Positive and Negative) into the combiner box. For this discussion we will assume the array consists of 6 solar panels in two parallel strings of three panels each.  Each string will include Positive and Negative connection cables, a breaker and a strain relief wire fitting.

Before you begin wiring, verify the polarity of each panel by connecting a voltmeter to its outputs. Once polarity is confirmed, wire the “home run” leads in the combiner box.  These are the wires that will connect to the Positive and Negative end of each series string of panels.  If your panels have connection cables then you will use MC4 cables for this.  MC4 cables are typically 30'-100’ long. One cable will be used for each string of modules. The cable has a male connector on one end and female on the other.  The cable will be cut into 2 pieces so you will end up with one piece that matches the Positive output from your panels and one that matches the Negative. The cut ends will run into the combiner box. Before you cut the cable, confirm that the cable has enough length to comfortably reach the Positive and Negative leads from each string.  Assuming your combiner box will be centrally located with respect to the layout of the panels, cut a single MC4 cable into two equal pieces.  If your combiner box is off-center from the panels, cut the cable at appropriate lengths such as 10' and 20' or 8' and 22', etc. for a 30’ cable.

Inside the combiner box note that the breaker comb and the negative bus bar each host a large wire lug for connecting heavier gauge transmission wire to run power to your charge controller or inverter. Verify that those wires have already been connected properly before continuing. (Correct torque settings are also very important to be aware of when making all connections.) Now route the cut ends of the MC4 cable for the first string through the first strain relief. Strip approximately 1/4" of insulation off each lead, and connect the Positive to the first breaker, and the Negative to the negative bus bar. Once connected, make sure the breaker is in the Off position. Repeat for the second leads using the second strain relief and breaker. Ensure that the breakers for each circuit are properly installed and stay in the Off position. Once connected, home run leads from the combiner box to the array may be set aside until ready to make the connection to each string’s leads.

A grounding conductor is required for PV arrays. This bonds all the panel frames together and to the rest of the system. As panels are installed to the racking be sure to attach ground lugs on each panel and run the grounding conductor from the PV array to the grounding lug in the combiner box.  Some racking systems are designed to bond the panel frames to the racking automatically so only one grounding lug is required for the whole array.  Make sure to read the racking installation manual to determine your system’s requirements.

Time to move to the series connections of the first 3 panels.  Plug a Positive (+) lead from one panel into the Negative (-) lead of a second panel.  Then plug the Positive lead of the second panel into the Negative lead the third panel. There are now two series connections for this string. Repeat this step with the second set of three panels.

Now there are two series strings of three panels each. There is a Positive lead at one end of each string and a Negative lead at the other end. These are the leads that eventually get connected to the home run leads of the combiner box. Verify polarity again using a voltmeter to confirm which leads on each string are Positive and which leads are Negative. Reversing polarity may cause permanent damage and void manufacturer warranties on your product.

Once all other system installation and wiring is complete, the final connections to the array can be made. Verify that all breakers are off before connecting the string ends to the combiner box home runs. Once connected, do a final polarity check inside the combiner box. Each string can be tested with a voltmeter for proper polarity and voltage. The circuit breakers should be left in the off position until it is time to commission the system. Congratulations, the array has been safely wired and tested and is ready to provide power to your system.

With over 40 years of experience, Backwoods Solar has the knowledge to help you with the correct system components for your solar electric system needs. Give Backwoods Solar a call today at 208-263-4290 to speak with one of our system designers.

We offer FREE technical support for the life of the system
when purchased from BWS!

26% Federal Tax Credit Ends 12/31/2020.
Click
here for more information.

Backwoods Solar 4th of July Hours


Backwoods Solar is observing the 4th of July Holiday and will be closed for business Friday, July 3rd. We will be back on the phones at 8:30 am Monday morning, July 6th. We hope you all have a safe and healthy Independence Day celebration.
Current Backwoods Solar
Business Operation and Procedures

For the continued health and safety of our customers and staff, Backwoods Solar continues to suspend all walk-in system design consultations and informational visits. As always, Backwoods Solar will continue our top-quality sales and support via phone and email. We're on the phones from 8:30 to 4:30 PDT Monday through Friday.

Local prepaid orders may be picked up at the front garage door of our facility adjacent to the Pack River Store. Please phone us ahead for details on your pre-paid local pick-up.

Backwoods Solar understands that these temporary policies and procedures may be an inconvenience and we regret if that is the case. Please call us at 208-263-4290 or email customerservice@backwoodssolar.com if you have any questions or concerns. 

Backwoods Solar wishes the best of health and safety to our solar energy family and friends and we look forward to resuming normal business operations as soon as possible. We appreciate your understanding during these unprecedented times.

Request a 2020 Planning Guide & Catalog


Our 160-page Planning Guide & Catalog is free and has the information you need to make smart choices in the design of your renewable energy solution. The first 30 pages consist of a planning guide that acts as a road map to help you navigate your path to energy independence. Learn about the design elements of off-grid, grid-tie and critical-load systems, among other topics of interest. Determine appropriate system size with included worksheets and system examples while reviewing over 120 pages of recommended product information in one compact volume.

Click here to request a free catalog today.You may also download a PDF version here.
Click here to read what others have to say about Backwoods Solar
Share Share
Share Share
Tweet Tweet
Forward Forward
Now accepting PayPal