Solar Combiner Box Wiring Diagram: Essential Installation Roadmaps

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. They will occasionally include conventional circuit diagrams intended for professional installers, though.

Pictorial schematics are by far the easiest 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:

Note: If you don’t get a wiring diagram with your combiner box, you can find them 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.

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.

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?

If 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 this will probably work if you have good general electrical knowledge. 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. This would be the safest action even if they charge you for the service.

What Detail Should the Wiring Diagram Include?

A good combiner box wiring diagram should clearly illustrate the box with all the internal components, such as circuit breakers and busbars, marked. It should also clearly illustrate the incoming and outgoing wires and where they are connected.

These include solar panel output wires, outgoing charge controller and battery bank cables, and ground wire connection points.

All internal components should have their respective ratings listed as well. For example, list circuit breaker or fuse voltage and amperage ratings on the wiring diagram. This goes hand-in-hand with clearly describing the box’s 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’ll likely encounter.

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 circuit breakers in disconnecting the relevant circuit in an over-current or short-circuit situation. The main difference between the two is 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 and replace 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 is 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 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.

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; the IEC covers the rest of the world. Their respective symbols differ but are similar enough to be easily recognizable.

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 in the bargain. If you are one of those weekend DIY warriors, here are some pointers for a great combiner box diagram.

NOTE: In a home-baked combiner box, a clear, well-detailed wiring diagram is crucial 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 know the system details clearly. 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.

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.

The first step is to draw up a component layout for your box, as illustrated below. Suppose 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 (CBs) or fuses, a negative busbar, and a ground busbar.

Typically, the fuses or CBs will be centrally located at the top of the box, and the two busbars on opposite sides towards the bottom. 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 and list 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 if you could 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, mark which input is which. You can also draw arrows on the wires indicating an incoming feed.

NOTE: When you assemble the box, keep the inputs and outputs in the same position or order as indicated in the diagram. Many accidents happen when folks work on a circuit’s live sections after isolating the wrong component.

Sketching Your Combiner Outputs to the Charge Controller and Battery Bank

The third and final step is drawing bridge pieces on top of the fuses or CBs and 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 have wiring diagrams; 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 it. Please comment below if you have any other information, suggestions, or questions regarding solar combiner boxes.