PV Combiner Box vs Junction Box: What’s the Difference?
Category: FAQ · Reading time: 4 min
In a solar PV system, both the junction box and the combiner box play protective and connective roles — but they sit at completely different points in the system and do different jobs. Confusing them is a common mistake when sourcing a bill of materials.
Solar PV Junction Box: On Every Module
The junction box is mounted on the back of each individual PV module. It houses bypass diodes that protect the module from hot-spot damage when part of the panel is shaded. It also provides the terminal where module cables connect. Think of it as the “heart” of a single module.
- Location: back of each PV panel
- Main job: bypass diodes + module wiring terminals
- Typical rating: up to 1500V DC
PV Combiner Box: Aggregating Many Strings
The combiner box sits between the PV array and the inverter. It collects the outputs of multiple strings (each string = a series of modules), combines them into a single DC bus, and adds protective devices — fuses or breakers per string, surge protection, and optional monitoring. It is the “control room” of the array.
- Location: near the array, before the inverter
- Main job: combine strings + fuse + surge protection
- Typical rating: 1000–1500V DC, 8–24 strings
Side-by-Side Comparison
| Aspect | Junction Box | Combiner Box |
|---|---|---|
| Position | On each module | Before inverter (array side) |
| Core function | Bypass diodes, module wiring | Combine strings, fuse, surge protection |
| Quantity per plant | One per module (many) | One per array / per inverter input |
| Buyer consideration | Diode quality, IP rating, cable seal | String count, fuse rating, IP65 enclosure |
Which Do You Need?
Every system needs junction boxes (they come with or are integrated into the modules). Combiner boxes are needed when multiple strings must be aggregated before the inverter — typical for medium and large rooftop or ground-mount projects. For single-string residential systems, a combiner box may be replaced by direct connection with DC breakers.
View our Solar PV Junction Box → · View our PV Combiner Box →
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