When you're wiring a solar array, the combiner box is where string currents meet before heading to the inverter. Get this choice wrong and you might end up with a box that can't handle your string count or that leaves your system under-protected. Combiner boxes also serve as a single disconnect point, letting you cut power to the whole array from one switch. The two options here take different approaches: one carries a 63A circuit breaker and dual surge suppressors, while the other packs a fuse, a circuit breaker, and a surge protector into a compact enclosure. Which one makes sense depends on your array layout, your current per string, and how much protection you want built in.
Quick verdict
If your priority is keeping the budget in check, the 4String Solar PV Combiner Box at $61.91 is the pick. If you'd rather pay for extra protection, the 2 in 2 Out Solar Combiner Box at $125.82 has you covered.
At a glance
| Feature | 4String Solar PV Combiner Box | 2 in 2 Out Solar Combiner Box |
|---|---|---|
| Price | $61.91 | $125.82 |
| Inputs / outputs | 4 in, 1 out | 2 in, 2 out |
| Max input per string | 10A | 20A |
| Circuit breaker | 63A, 550V | 20A DC500V |
| Surge protection | 2 SPDs, 40KA 600V | 1 SPD, 40KA DC500V |
Where the 4String wins
The 4String carries two surge protection devices rather than one, giving it a wider shield against voltage spikes. It also comes with a wall-mount design and mounting plates in the box, so you can hang it on a wall without ordering extra brackets. That wall-mount convenience is especially useful if you're running conduit to a central location.
Where the 2 in 2 Out wins
The 2 in 2 Out includes a 20A DC fuse on top of its circuit breaker and surge protector, so you have a complete safety chain from the start. It also keeps a compact footprint at 11.73 x 11.73 x 5.51 inches, which is helpful if your electrical space is tight. That fuse alone is enough to tilt the decision for many DIY solar builders who would rather not buy a separate fuse holder.
Product notes
4String Solar PV Combiner Box 63A Circuit Breaker Solar Panel System Waterproof
The IP65-rated enclosure is the standout feature, defending against water jets and dust, so this box can live on an exterior wall without issues. The wall-mount style and included mounting plates also simplify installation, and natural convection cooling handles temperature control passively. The per-string current ceiling is the real constraint: rated at 10A per input, this box is ideal for standard residential panels but less suited to larger, high-current modules. If all four of your strings sit within that limit, the setup is straightforward; if any string peaks above 10A, you'd need to split it. That single limitation is the main reason to look elsewhere.
2 in 2 Out Solar Combiner Box, PV Combiner Box with 20A PV Fuse, DC 20A Circuit Breaker
The 2 in 2 Out is a compact unit that fits into tight electrical spaces, with dimensions of 11.73 x 11.73 x 5.51 inches. Its 20A per-string input rating is a strong reason to choose this box if your panels feed more current per string. That headroom alone can make the higher price worthwhile for a high-current array. The trade-off is the two-input layout: with only two inputs and two outputs, you'll need to think carefully about how many strings you're combining. For a two-string array, it's a clean solution; for anything larger, you'd add another combiner.
Final choice by use case
For a system with several separate strings, the 4String Solar PV Combiner Box is the practical choice. For a more compact setup, the 2 in 2 Out is the one to get. The final decision comes down to whether you value extra input capacity at a lower price or extra protection components in a smaller footprint.
