Solar balance-of-system wiring has a bottleneck moment: several PV strings all need to merge safely into one feed before reaching the inverter. A combiner box is that junction point, and the choice usually comes down to how much current each string is carrying and how much you want to spend. This head-to-head looks at the 2-string solar combiner box with a lightning arrester and the 2-in-2-out combiner box with heavier PV fusing to help you pick the right one for your array.
Quick verdict
Choose the 2-string Solar DC PV Combiner Box at $74.99 if you have two strings, want a higher system voltage, and your per-string current stays within a 15A fuse rating. Choose the 2-in-2-out Solar Combiner Box at $125.82 if you need 20A per-string current, a second output path, and a matched set of fuse, breaker, and surge protection.
At a glance
| 2-string box | 2-in-2-out box | |
|---|---|---|
| Price | $74.99 | $125.82 |
| PV string layout | 2-string input | 2 in, 2 out |
| Per-string fuse | 15A DC | 20A DC |
| System voltage | 600V | 500V |
| Protection package | Fuses, lightning arrester, 600V 63A breaker | 20A fuse, 20A MCB, Class T2 SPD |
| Housing dimensions | 9 x 5.1 x 9 inches | 11.73 x 11.73 x 5.51 inches |
Where each product wins
Where the 2-string box wins
- It costs less upfront.
- It supports a higher system voltage than the 2-in-2-out box.
- Its smaller footprint is easier to fit in tight spots.
Where the 2-in-2-out box wins
- It handles higher per-string current.
- It gives you two input pairs and two output pairs.
- Its protection package pairs a per-string fuse with a breaker and a Class T2 surge protector.
Product notes
2-String Solar Combiner Box with Lightning Arrester
This is the straightforward two-string option. It brings two PV strings into a single protected feed, with a DC fuse set, a circuit breaker, and a lightning arrester in one enclosure. The housing carries an IP65 waterproof rating. If your array is already designed around two strings and your per-string current is moderate, this box keeps the cost and the enclosure size down. The main limitation is the per-string fuse rating: a high-current string would be outside what the fuses are meant to protect. It also is built as a two-string combiner, so you are not getting a second independent output set.
2-in-2-Out Solar Combiner Box
If your strings are on the high-current side, this box is the more capable match. It supports two PV inputs and two outputs, and the protection package lines up with heavier per-string currents: a DC circuit breaker, a DC fuse, and a Class T2 surge protective device all in the same enclosure. The 500V system rating goes with a 20kW capability, so it is positioned for larger arrays. The housing is made from ABS and polycarbonate and measures 11.73 by 11.73 by 5.51 inches. Choose it when you want per-string fusing and overcurrent protection matched to more demanding strings. The tradeoff is the physical size and the extra cost; the larger footprint reflects the bigger capacity, so give it enough clearance.
Final choice by use case
- Choose the 2-string Solar Combiner Box when you want a lower price, a two-string layout, and lighter per-string currents.
- Choose the 2-in-2-Out Solar Combiner Box when you are running a heavier-current array and want a breaker, fuse, and surge protection in one box.
