Sizing guide
DCDB 1 in 1 out vs multi string: choosing the right configuration
The naming on a DCDB listing looks cryptic until you know what it is counting. Once you do, picking the right one takes about a minute.
Product listings for DCDB boxes often use shorthand like 1 in 1 out or 2 in 1 out, and if you have not come across it before, it reads like a spec you need a manual to decode. It is actually simpler than it looks.
What the numbers mean
The first number is how many string inputs the box accepts, meaning how many separate panel strings can be wired into it. The second number is how many combined outputs it sends onward to the inverter. So a 1 in 1 out box takes a single string in and passes it straight through, with protection in the middle but no actual combining involved. A 2 in 1 out box takes two separate strings and merges them into one protected output. A 4 in 2 out box takes four strings and combines them into two separate outputs, useful for an inverter with two MPPT trackers that each want their own combined feed.
When 1 in 1 out is the right call
If your array is wired as a single string, which is common on smaller residential systems with a straightforward, unshaded roof, a 1 in 1 out DCDB is the correct and simplest choice. You still get the DC MCB and surge protection device, just without any combining function, because there is nothing to combine.
When you need a multi string configuration
Once your array is split across two or more strings, whether because of roof shading, multiple orientations, or an inverter with multiple MPPT inputs, you move into 2 in 1 out or higher. The general rule is that the DCDB's input count should match your actual string count, and the output count should match how many separate feeds your inverter expects.
This is also where it is worth checking your inverter's own MPPT count rather than guessing. An inverter with two independent MPPT trackers generally wants two separate combined outputs from the DCDB, not one large combined feed, since combining strings that feed different trackers defeats the purpose of having separate trackers in the first place.
A quick way to work it out
Count your actual physical strings on the roof or array. Check your inverter's MPPT input count. Match the DCDB's in and out numbers to those two figures. If the two numbers do not divide evenly, for example five strings into two MPPT inputs, tell us the exact layout and we will confirm a configuration that fits rather than trying to force a standard listing to match.
We build DCDB boxes from 1 in 1 out up through full multi string configurations. Send your string count and MPPT count through the contact page or on WhatsApp and we will confirm the right box before manufacturing.