If you have a solar combiner box with a confusing or missing wiring diagram, you’ll have to find a better example, seek advice on deciphering it, or even draw one up yourself.

We can help you do this by describing the different types of diagrams you may encounter and how to find, read, and understand them. We’ll also describe the different symbols and terminology used in wiring diagrams to describe solar panels, circuit breakers, and fuses, to name a few.

To wrap up, we’ll also give a brief step-by-step tutorial on designing your own wiring diagram for a custom DIY solar combiner box build.

What Are The Different Types of Wiring Diagrams for a Solar Combiner Box?

Most wiring diagrams supplied with commercial combiner boxes are simple, easy-to-understand pictorial type schematics. Occasionally they will also include conventional circuit diagrams intended for use by professional installers, though.

Pictorial schematics are by far the easier type to use for laymen and DIY enthusiasts. Typically, circuit diagrams are made of logically presented line drawings with components illustrated as electrical circuit symbols. If you are from an electrical background, they will make sense. If not, a pictorial schematic will be a lot easier to use.

Here is an example of a simple combiner box, a conventional electrical circuit diagram, and a pictorial schematic.

Solar Combiner Box Wiring Diagram

Credit: Paul Scott

Conventional electrical circuit diagram

Pictorial schematic wiring diagram

Credit: Paul Scott

Note: If you don’t get a wiring diagram with your combiner box, they can usually be found on the manufacturer’s website documentation downloads or technical support.

The wiring diagrams for combiner boxes will usually be accompanied by illustrations detailing the mounting, electrical components, and the box’s input and output wiring points, as illustrated below.

Courtesy of Amazon.com

Credit: Paul Scott

Do I Really Need Wiring Diagrams for My Solar Combiner Box?

Yes, you do. Most solar combiner boxes are internally pre-wired with MC4 compatible connectors and only require the addition of the outputs to the rest of the PV system. See below.

Example of a pre-wired combiner box. Courtesy of Amazon.com

However, some combiner boxes are not pre-wired, and a wiring diagram will be essential. And even with pre-wired boxes, a diagram will ensure you get all the outgoing wiring connected correctly.

What if I Can’t Find Any Wiring Diagrams for My Solar Combiner Box?

In the unlikely event that you cannot find any wiring information for your solar combiner junction box, you have two choices.

The first, and least desirable choice, is to find a diagram for a combiner box of similar specs and layout and use that as an example. Most combiner boxes feature similar layouts and components even if they are different brands, so if you have good general electrical knowledge, this will probably work. That said, it’s not generally advisable.

The second choice, and the safest option by far, is to take the combiner to a solar installer and have them assess the situation and draw you up a wiring diagram. Even if they charge you for the service, this would be the safest course of action.

What Detail Should the Wiring Diagram Include?

A good combiner box wiring diagram should have a clear schematic illustration of the box with all the internal components such as circuit breakers and busbars clearly marked. It should also clearly illustrate each of the incoming and outgoing wires and exactly where they are connected. These would include solar panel output wires, outgoing cables to the charge controller and battery bank, and ground wire connection points.

All internal components should have their respective ratings listed as well. For example, you should clearly list circuit breaker or fuse voltage and amperage ratings on the wiring diagram. This goes hand-in-hand with a clear description of the box’s overall safe maximum voltage and current input specifications.

Understanding Wiring Diagrams for a Solar Combiner Box – Common Symbols and Terminology

You’ll often encounter commonly used symbols and terminology in solar combiner box wiring diagrams, especially non-pictorial types. Let’s take a closer look at the most common symbols and terminology you’re likely to come across.

Common Terms

Circuit Breaker

A switch is used to either manually disconnect or isolate a circuit or automatically open and disconnect in the case of a short circuit or a surge in current. In combiner boxes, circuit breakers are normally single-pole, meaning they have only one set of contacts for use with a single incoming cable.

Fuse

Fuses are similar to a circuit breaker in that they disconnect the relevant circuit in case of an over-current or short circuit situation. The main difference between the two is the fact that fuses are usually not mechanical. When the rating of the fuse exceeds, they rely on a thin wire or filament that burns through or “blows”. This effectively disconnects or isolates the affected circuit. You can manually remove many fuse types from the circuit to isolate them then replaced them when desired.

Busbar

A busbar is a conductive metal strip or rail with multiple connection points. This allows multiple incoming cables to combine into a single component. The outgoing wire also connects to the busbar giving continuity between incoming and outgoing elements. Busbars are most commonly used to combine the incoming negative or ground leads from the solar panels.

Bridge Bar

This a metal strip with several individual “fingers” used to connect or bridge the outgoing terminals of circuit breakers and fuses. They are installed on the side of the circuit breaker opposite to the incoming positive wires. Much like a busbar, they form a single output from multiple inputs.

Enclosure

The enclosure is the physical box the combiner components are mounted in.

Terminal Strip

A terminal strip is the same as a busbar but is generally made of ABS composite rather than metal.

Common Circuit Symbols

Pictorial wiring diagrams are fairly easy to understand because they graphically depict a solar panel, circuit breaker, etc. Schematic diagrams use symbols to indicate their components and can be a little tricky to understand. Fortunately, many online resources have extensive lists of solar and general electrical symbols for reference. Here are the most common symbols with their descriptions.

Note: Two international electrical standards bodies dictate and control these symbols. The NEC covers North America, Canada, and parts of South America, and the IEC covers the rest of the world. Their respective symbols differ but are similar enough to be easily recognizable.

Common solar electrical circuit symbols.

Credit: Paul Scott

Drawing up Your Own Wiring Diagram for a DIY Solar Combiner Box

For the dedicated DIY enthusiast, building a custom combiner box often delivers the best results at about a third of the cost of a store-bought box. Not to mention being a lot of fun into the bargain. If you are one of those weekend DIY warriors, here are some pointers to get a great combiner box diagram.

NOTE: In a home-baked combiner box, a clear, well-detailed wiring diagram is a crucial element for several reasons. It will make fault finding easier and, perhaps most importantly, make it safe and easy for third parties to work on the box. You may have to call in a professional to sort out complex system problems at some point. A well-executed wiring diagram will be an invaluable aid for them.

Mind Map Your Combiner Box

If you’ve decided to build a custom combiner box, you’ll probably wire the entire solar system yourself. In this case, you’ll already have a clear idea of the system details. In other words, you’ll know how many solar panels you’ll use, whether they will be wired in series or parallel, and what type and size of a charge controller or inverter you’ll need.

At this point, you’ll need a pencil, a notepad, and a cup of excellent coffee.

Sketching Your Combiner Component Layout

To illustrate this whole process, we’ll use the diagram below as a reference.

Combiner Box Wiring Diagram step-by-step

Credit: Paul Scott

The first step is to draw up a component layout for your box, as illustrated below. Let’s assume you have 2 series-wired solar panel strings and a single charge controller in your system. For a basic combiner box, based on that, you will need two circuit breakers (CB’s) or fuses, a negative busbar, and a ground busbar.

Typically the fuses or CB’s will be centrally located at the top of the box and the two busbars on opposite sides towards the bottom of the box. Sketch the components in those positions in the box. It’s not necessary to try and draw complex images. Just use basic generally recognized symbols as illustrated. Make sure to annotate or write in the component names as well as listing CB or fuse ratings.

Sketching Your Array Inputs to the Busbars and Circuit Breakers

For step two, draw in your wire inputs from the panel strings. Again, no need for anything fancy. Straight-line wire representation will be fine. It would help, though, if you can draw positive, negative, and ground wires in different colors. To avoid confusion, draw a bridge or a break in the wire where two wires cross each other in the diagram. In addition, clearly mark which input is which. You can also draw in arrows on the wires indicating an incoming feed.

NOTE: When you do the actual assembly of the box, keep the inputs and outputs in the same position or order as indicated in the diagram. Many accidents happen where folks are working on live sections of a circuit after isolating the wrong component.

Sketching Your Combiner Outputs to the Charge Controller and Battery Bank

The third and final step is drawing in any bridge pieces on to of the fuses or CB’s as well as the output wires to the charge controller. As always, clearly label the output wire on the diagram. Once finished, the diagram is complete, and you can enjoy the coffee.

This is a straightforward, basic combiner box, and you may want to add other components such as lightning arrestors, system monitors, or rapid shutdown components. Fortunately, these components will themselves have wiring diagrams, and adding them to your diagram later shouldn’t be too much trouble.

In Closing

We hope this article has helped you make sense of the role and importance of the solar combiner box wiring diagram and how to interpret them. If you have any other information, suggestions, or questions regarding solar combiner boxes, please leave a comment below.

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