Start with the inverter layout when choosing between a 2 string and a 4 string solar combiner box. Confirm which PV strings may be combined, how many electrically separate output groups the design requires, and whether each receiving inverter input can accept the resulting voltage and current.
Four string inputs do not necessarily mean one combined output or four independent MPPT channels. Boxes sold as “4 string” can have different input-to-output arrangements. Ask for the grouping drawing before comparing them as equivalent offers.
This guide helps project buyers compare configurations and prepare an enquiry. It is not a wiring procedure or a substitute for a qualified PV designer’s assessment.
A PV string is a series-connected group of modules. An input is a physical connection to the proposed equipment. An MPPT is an inverter function that tracks an operating point. Physical inverter connectors and independent trackers need not have the same count.
You can see the distinction in manufacturer documentation: SMA lists independent MPP inputs, current limits and strings per input as separate fields. Check those fields for the inverter in your project; another model’s limits are not design values for your system.
Get the exact inverter model and approved string schedule before selecting a combiner box. Together, they show the grouping the box must support.
| Selection question | A two-input arrangement | A four-input arrangement |
| How many PV strings enter? | Confirm two string circuits on the drawing | Confirm four string circuits on the drawing |
| How are they grouped? | They may be combined or kept separate, depending on the design | One or several output groups may be proposed |
| How many MPPTs are served? | Determine from the circuit grouping and inverter documentation | Determine from the circuit grouping and inverter documentation |
| Which current matters downstream? | The current of each actual output group | The current of each actual output group |
| What makes an offer comparable? | Identified input/output grouping, ratings and components | The same evidence; extra inputs alone are insufficient |
Use the table as a set of comparison questions. A string-count label alone is insufficient to define how every product is wired.
The output count matters as much as the input count. BENY lists both a four-input/two-output arrangement และ four-input/four-output arrangement. These are different products; their ratings and approvals must not be transferred to OOHMAGE equipment.
First, ask the PV designer which strings are assigned to each inverter tracker and which combinations that inverter permits. The proposed combiner drawing should preserve those assignments.
Consider a project schedule with four strings assigned across two independent MPPTs. An offer described only as “4 in, 1 out” does not show whether it keeps those circuits separate. Ask for a drawing that identifies which inputs join each output and where each output connects at the inverter.
This is a check of the proposed documents, not a circuit to install. Do not join separate MPPT circuits because the enclosure happens to have enough cable entries.
Weidmüller’s PV Next documentation identifies inputs, outputs and electrically separated tracker arrangements within its range. Request the same level of clarity for the box you are considering.
When compatible parallel strings are combined, the shared output path carries more current. The inverter’s permitted input current does not increase with it. Check both the output path and the receiving input against the proposed design.
Have the designer confirm that the module and string characteristics, including the relevant voltages, are compatible within each proposed combined group.
Check separately:
Weidmüller’s fact sheet on combining PV strings explains why combined current must be checked against the inverter datasheet. A larger enclosure cannot make an incompatible inverter input suitable.
Ask the designer for the design currents and applicable corrections. Module wattage or a single universal current multiplier is insufficient for selecting the complete box.
String count also tells you little about the required DC voltage rating. Use the actual module data, series-module count, site temperature assumptions and inverter voltage limits.
Ask for a component list with the relevant DC ratings and functions of the offered configuration. A fuse link is distinct from its holder; a protective device is distinct from a switch-disconnector; and a surge protective device is distinct from protection against sustained abnormal voltage.
The actual array design, module limits and applicable requirements determine whether string overcurrent protection is needed and how it is coordinated. Do not assume every two-string system uses the same fuse or every four-string box includes the same protective devices.
Compare documented configurations against the same project inputs. The largest ampere number in a product listing is not, by itself, a useful basis for the decision.
Spare input positions help with expansion only if the future arrangement suits the complete system. Assess the enclosure, components, output path and inverter against that future configuration.
Before paying for spare positions, establish what they actually permit. Are the necessary components included? How are unused entries closed? Would added strings change output current, protection requirements or tracker grouping? Can the existing inverter accept them?
Document the agreed future arrangement separately from the initial supply. “Space for four strings” is not a promise that any four-string array can be added later.
Use the following checklist to get two offers onto the same project basis:
| Item to confirm | Information to supply or request |
| Array information | Module datasheet and approved string schedule |
| Receiving equipment | Exact inverter model and relevant input documentation |
| Circuit grouping | Inputs and outputs assigned to each MPPT |
| Electrical design | Required DC voltage and design current for each circuit group |
| Included components | Identified fuse links, holders, switching devices and SPDs, as applicable |
| เงื่อนไขการติดตั้ง | Mounting environment, enclosure requirement and cable-entry arrangement |
| Connectors | Manufacturer, exact connector type and permitted mating combination |
| Order documents | Configuration drawing, component list and available supporting documents |
For help reading the proposed drawing, use our solar combiner box diagram guide alongside the project’s approved documents. This comparison focuses on how the inputs are grouped.
ดู OOHMAGE combiner-box range, then send the exact inverter model, approved string schedule, required input/output groups, electrical design data, installation conditions, quantity and destination market with your configuration enquiry.
Before ordering, confirm the proposed drawing, component list and configuration. Do not infer string count, MPPT arrangement or included components from the series name alone.
Possibly, if the manufacturer and PV designer confirm that exact partial-use arrangement. Check the protection, unused entries, grouping and receiving-equipment compatibility; the input count alone is insufficient.
No universal rule follows from having two strings. Check the inverter inputs, required protection and installation design to determine whether external combining or protection is needed.
Do not assume so. A box with four incoming string circuits does not necessarily provide four independent tracker channels. Check the circuit-grouping drawing and inverter documentation.
