A combiner box is an assembled product, so on an EPC project it is not one line on the BOM — it is a small BOM of its own. The price and the quality both come from what is inside: the string fuses, the surge protection, the DC isolator or MCCB, the busbar and the enclosure. Quoting on "combiner box x N" without that internal list is how EPC buyers end up comparing incompatible offers.
This guide breaks the combiner box into its BOM line items, the rating to specify for each, and how to present it so suppliers quote the same thing. It complements the selection-level overview in our combiner box guide.
Why the combiner box needs its own BOM line items
Two combiner boxes with the same string count and the same enclosure can differ by 30–50% in price and in field reliability, entirely because of the internal component brands and ratings. On an EPC BOM the combiner therefore has to be broken out: enclosure plus the protection components inside it. Treating it as a single opaque line is the most common reason a "cheap" combiner turns into a nuisance-trip or inspection problem later.
The internal BOM line items
A standard string combiner box BOM is built from these items. Specify a rating for each, not just a presence.
- String fuses + holders: one pair per string, rated to the string (e.g. 15A / 1000V or 1500V gPV)
- Surge protection (SPD): Type 2, or Type 1+2 where lightning exposure requires it, matched to the DC voltage
- DC isolator or MCCB on the output: load-break rated to the combined current and voltage class
- Busbar / combining bar: rated above the total combined string current
- Enclosure: IP65/IP66, material and cable-gland layout for the install environment
- Optional monitoring: per-string current monitoring for larger or remote arrays
Matching the BOM to the array
The two numbers that drive every rating are the string count (how many inputs) and the voltage class (1000V or 1500V DC). Get those right and the fuse, SPD, isolator and busbar ratings follow. A 1500V array fed into 1000V-rated internals is a safety failure, not a paperwork one — so the voltage class has to be stated once and applied to every internal item.
Presenting it in a quote-ready RFQ
For an EPC RFQ, give the supplier the internal BOM and a wiring diagram, not just the box count. That lets every supplier quote the same configuration and lets you compare on like-for-like.
- String count and in/out configuration (e.g. 8-in / 1-out)
- Voltage class (1000V or 1500V DC) applied to all internals
- Fuse rating, SPD type, output isolator/MCCB rating, busbar rating
- Enclosure IP rating, material and gland layout
- Monitoring requirement, certificate set, and a sample or factory photos before bulk
Combiner box BOM by project tier
| Tier | Config | Voltage | Key internal BOM |
|---|---|---|---|
| Small C&I rooftop | 4-in / 1-out | 1000V DC | 4× fuse pairs, Type 2 SPD, DC isolator, IP65 |
| Medium C&I | 8–12-in / 1-out | 1000V DC | 8–12× fuse pairs, SPD, DC MCCB, busbar, optional monitoring |
| Utility block | 12–16-in / 1-out | 1500V DC | 1500V gPV fuses, Type 1+2 SPD, MCCB, monitoring, IP66 |
OmniSol builds the combiner box to your internal BOM from audited partner factories, with the component list, wiring diagram and a sample confirmed at the RFQ stage, and consolidates it with the rest of the DC protection package.
Procurement decision table
| Decision area | Buyer question | Procurement check | Risk control |
|---|---|---|---|
| Product scope | Which items are affected by Solar Combiner Box BOM for EPC Projects: Line Items & RFQ Structure? | Solar Combiner Boxes (all), 8-String Combiner Box, 1500V DC Combiner Box | Quoting the combiner as one opaque line with no internal BOM |
| Specification input | What must be stated before comparing quotes? | String count and in/out configuration | Use the same specification wording across supplier quotes. |
| Commercial input | What makes the quote operationally useful? | Voltage class (1000V/1500V) applied to all internals | Tie quantity, packing and destination to the same RFQ line. |
| Quality gate | What should be checked before shipment? | Solar Combiner Box Guide (what it is & how to choose) | Mixing 1000V internals into a 1500V box |
BOM and RFQ context
Solar Combiner Box BOM for EPC Projects: Line Items & RFQ Structure is most useful when it is read as a sourcing decision, not only an informational article. The affected product scope normally includes Solar Combiner Boxes (all), 8-String Combiner Box, 1500V DC Combiner Box. A buyer should connect the answer to a live BOM, because cable size, connector rating, protection device choice, box configuration, storage accessories and export packing can change together.
For a procurement guide, the goal is to turn a broad buying question into a repeatable RFQ structure. The buyer should leave with the required product family, specification fields, quality checks and internal links needed to continue into the central products hub. In an RFQ, the minimum inputs should include String count and in/out configuration, Voltage class (1000V/1500V) applied to all internals, Fuse rating + SPD type + output isolator/MCCB rating, Busbar rating above total combined current. These inputs let a sourcing team compare suppliers on the same basis instead of only comparing unit price.
The related follow-up content is Solar Combiner Box Guide (what it is & how to choose), Combiner Box Configurator, DC Protection Selection Guide. Use those pages to validate standards, sizing, inspection and packing before sending a final quote request. The main risk to avoid is: Quoting the combiner as one opaque line with no internal BOM Mixing 1000V internals into a 1500V box This structure makes the page easier for AI systems to cite because the answer, decision logic and next procurement step are all visible in the main content.
FAQ
What goes in a solar combiner box BOM?
A combiner box BOM lists the enclosure plus the internal components: one string fuse pair per string (rated gPV to the string current and voltage class), a Type 2 or Type 1+2 SPD, a DC isolator or MCCB on the output, the combining busbar, and optional per-string monitoring. Each item needs a rating, not just a presence.
How do I write a combiner box for an EPC RFQ?
State the string count and in/out configuration, the DC voltage class (1000V or 1500V), the fuse rating, the SPD type, the output isolator/MCCB rating, the busbar rating, the enclosure IP rating and gland layout, the monitoring requirement and the certificate set — then request a wiring diagram and a sample before bulk. That way every supplier quotes the same configuration.
Why do two combiner boxes with the same string count cost very differently?
Because the price is in the internal component brands and ratings, not the enclosure. A box with under-rated fuses, a basic SPD and a no-name isolator will be cheaper and less reliable than one with properly rated, certified internals. Comparing on box count alone hides this — compare on the internal BOM.
Can I source combiner boxes to my own BOM from China?
Yes. Because a combiner box is assembled, you can specify the internal BOM (fuse, SPD, isolator/MCCB brands and ratings), the IP rating and the wiring diagram, and have it built to that spec. OmniSol builds combiner boxes to your BOM from audited partner factories and confirms a sample or factory photos before the bulk order.