Passthrough Box - 1 Series String, No Parallel Connections

What is a passthrough box?

A solar passthrough box, also sometimes called a roof penetration box, solar combiner box (in some contexts), or transition box, is a crucial component in a rooftop solar panel installation. It provides a safe, weatherproof, and code-compliant way to transition the wiring from your solar panels on the roof to the conduit that runs down through your attic or walls (the "homerun") and eventually to your electrical panel or inverter.

All of our passthrough boxes are custom and designed for your project, so will look different then what's in the picture. Shown is a MidNite Solar MNPV6-MC4-LV-SPD300, which is a typical pass through box for a single low voltage string with six parrellel connections.

Each pass-through box includes:

One outdoor rated, rainproof enclosure.

Prewired MC4 positive and negative terminals for each series string

Strain relief installed for each series string

Strain relief installed for ground wire

Independent over current protection for each series string

Surge Protection Device installed

Negative and ground bus bar and/or terminal blocks

What's not included (that you may need):

Additional PV wire to connect solar panels to passthrough box

Conduit adapter, conduit, and wire to connect the pass-through box to the inverter

An external DC Disconnect switch

Ground wire and ground lug to connect the racking to the pass-through box

Information we need:

How many series strings will connect from the passthrough box to the inverter?

How many strings will be connected in parallel?

What is the exact model of solar panel being used?

Where do you want to mount the box?

We will design your custom pass through box based on this information. If you don't know the answers to these questions, we would recommend that you purchase a Professional Design Package.

Here's a breakdown of its purpose and key features:

Features:

• Weatherproof Enclosure: The primary purpose is to protect the electrical connections between the solar array wiring and the homerun conduit from the elements (rain, snow, UV exposure, etc.). This prevents damage, corrosion, and potential electrical hazards.
• Organized Transition Point: It acts as a central point where multiple strings of solar panels can be combined (if necessary) before transitioning into a single (or fewer) conduit(s) for the homerun.
• Code Compliance: Building and electrical codes require specific methods for penetrating roofs and transitioning between different wiring types. Passthrough boxes help meet these requirements, ensuring a safe and inspected installation.
• Accessibility for Maintenance: Provides a convenient location to access and troubleshoot connections if needed.
• Grounding Connection: includes grounding terminals to properly ground the solar array and the enclosure itself. The grounding conductor must be brought to earth ground with home run.

Key Features:

• NEMA 3R Enclosure: These ratings indicate that the box is designed for outdoor use and provides protection against rain, sleet, and snow.
• Roof Flashing (often integrated): A critical component is the flashing. Many passthrough boxes come with integrated flashing that is designed to seal against the roofing material, preventing water leaks around the penetration. Rail mounted boxes do not include flashing.
• Conduit Knockouts/Entry Points: The box will have pre-drilled holes or knockouts to allow for easy connection of conduits of different sizes. Depending on configuration you may need to drill out holes for conduit fittings.
• Terminal Blocks or Connectors: Inside the box, you'll find terminal blocks, bus bars, or other types of connectors that allow you to securely join the solar panel wires to the homerun wires.
• DIN Rail: Some boxes are equipped with a DIN rail for mounting components like fuse holders, circuit breakers, or surge protectors.

Why is it Important in the Solar Array to Homerun Connection?

• Prevents Roof Leaks: Proper flashing and sealing are crucial to maintain the integrity of your roof. A poorly installed penetration can lead to costly water damage.
• Protects Electrical Connections: Exposure to the elements can degrade electrical connections, leading to reduced system performance, faults, or even fires.
• Maintains System Efficiency: A well-organized and properly wired transition ensures optimal power flow from your panels to your electrical system.
• Simplifies Installation: Provides a standardized and organized approach to connecting the solar array, making installation faster and easier for installers.

A solar passthrough box is a vital component for any rooftop solar installation. It ensures a safe, reliable, and weatherproof connection between your solar array and the rest of your electrical system, helping to protect your investment and maximize your solar energy production. Always ensure that the chosen passthrough box meets local code requirements and is suitable for your specific roofing and solar panel system. And, most importantly, that it is installed correctly to prevent water intrusion.