Short answer: a PV combiner box is the junction where several solar strings are paralleled into one DC feed. Inside it sit five things: string protection (fuses or DC breakers), a DC surge protective device, a means of isolation, monitoring or metering, and an enclosure rated for outdoor or rooftop duty. Each is a separate ordering line, and the box is only as good as the least-specified part.
This page lists those components in the order they are usually specified, with the confirmed CHINT parts we can quote and the places where a code must be verified against the array before a quotation is issued. It is written from the position of an independent trading company, not a manufacturer and not an appointed distributor of any brand: certificates are stated per exact ordering code, never for a whole range.
What a combiner box is for
Strings are paralleled because a single DC run to the inverter is cheaper and simpler than one run per string. The box does three jobs: it gathers the strings, it protects each string from a fault in another, and it gives the array a single point for isolation and surge protection. In a recombiner or array box, several combiner boxes are gathered again for a large plant; a string box serves a smaller installation directly.
| Function | Typical component | What it is specified by |
|---|---|---|
| String protection | String fuse or DC-rated breaker | String Isc, the string voltage class, and whether the array is fused or breaker-fed |
| Surge protection | DC SPD | Ucpv above the array maximum system voltage, impulse current, Up |
| Isolation | DC-rated load-break switch or isolator | DC voltage class and the load-break duty on a live array |
| Monitoring | DIN-rail energy meter or string monitoring | Phase, direct or CT, and the communication bus |
| Enclosure | Wall or pole enclosure | IP rating, UV exposure, and internal space for the DC devices |
String protection: fuse or DC breaker
On the DC side the protective device is specified on the string’s short-circuit current and the array voltage, and it must be DC-rated. A standard AC miniature circuit breaker is not a substitute — the DC side has no zero crossing to help the arc extinguish. The confirmed CHINT part here is the NB1-63DC, a DC circuit breaker to IEC/EN 60947-2 for PV and telecom duty, In up to 63 A, where the pole count sets the DC rating: 1P DC 250 V, 2P DC 500 V, 4P DC 1000 V, at Icu 6 kA at the matching voltage.
Where the design calls for string fuses instead, that is a separate component and a separate ordering code. We will not name a fuse code we have not verified against the factory documentation — tell us the string Isc, the voltage and the fuse-holder style and we confirm the part.
Surge protection inside the box
The combiner box is the natural home for the first stage of DC surge protection, because it sits close to the strings and limits a surge before it travels down the DC trunk. A second stage at the inverter DC input is common on long runs. The DC SPD is specified with a Ucpv above the array’s maximum system voltage at the lowest expected module temperature, an impulse current matched to the exposure, and a voltage protection level below the withstand of the equipment it protects. For the ordering code we confirm the Ucpv and impulse figures against the array voltage before quoting.
Isolation and switching
A combiner box needs a way to isolate the DC feed for maintenance, and with a live array that means a DC-rated device, not a guess. The DC breaker above provides isolation when it is the string device; a separate DC-rated load-break switch is used where the design isolates the whole box. As with the fuse, a specific DC isolation code is confirmed against the box’s voltage class before it is quoted rather than named from memory.
Monitoring and metering
If the box reports energy or current, the meter sits on the enclosure rail. The confirmed CHINT DIN-rail meters are the DDSU666 (single-phase), DTSU666 (three-phase four-wire), DSSU666 (three-phase three-wire) and the CT-operated DTSU666-CT, all with RS485 Modbus-RTU for a BMS or energy dashboard. Where only a local readout is wanted, the PA/PZ666 digital instruments cover volt and ampere display. On the AC side of the same plant — the inverter output and the entry cabinet — a standard 230/400 V SPD applies: the NU6-I+II (Class I+II) or NU6-II (Type 2) families to IEC/EN 61643-11.
| Component | Confirmed CHINT part | Confirmed basis |
|---|---|---|
| DC string breaker | NB1-63DC | IEC/EN 60947-2; DC 250 V (1P) / 500 V (2P) / 1000 V (4P); In ≤63 A; Icu 6 kA |
| DC SPD | Code confirmed per array voltage | Ucpv and impulse current verified before quoting |
| String fuse / holder | Code confirmed per string Isc | Verified against the string voltage class before quoting |
| DC isolation | Code confirmed per box voltage class | DC-rated load-break duty verified before quoting |
| Monitoring meter | DDSU666 / DTSU666 / DSSU666 / DTSU666-CT | RS485 Modbus-RTU; DTSU666-CT carries MID B+D |
| AC-side SPD | NU6-I+II / NU6-II | IEC/EN 61643-11; published VDE, CB, CE, RoHS / TÜV, CB documents |
The enclosure
The box itself is part of the specification, not an afterthought. Rooftop and outdoor duty drives the IP rating and the UV and temperature range, and a common failure is an enclosure too small for the DC devices once the leads and glands are counted. Where a small IP65 housing is wanted, the NXW1-3/5 IP65 enclosures are the confirmed shell family; they are a housing, and the devices inside them are still specified line by line. State the mounting (wall or pole), the environmental exposure and the internal space you need, and the enclosure is quoted against that.
FAQ
Q: What is the minimum set of components in a combiner box?
A: String protection, a DC SPD, a means of isolation, and a suitable enclosure. Monitoring is added when the plant reports energy or string current. Each is a separate ordering line.
Q: Can I use a normal MCB for string protection?
A: No. The DC side needs a DC-rated device; the confirmed part is the NB1-63DC to IEC/EN 60947-2, with pole count setting the DC voltage rating. An AC MCB is the wrong device for a PV string.
Q: How many poles for a 1000 V string?
A: On the NB1-63DC a 4-pole device is rated DC 1000 V, a 2-pole device DC 500 V, and a 1-pole device DC 250 V. Pole count is the voltage rating on the DC side, not a current rating.
Q: Where does the DC SPD go — in the box or at the inverter?
A: The combiner box is the natural first stage because it sits near the strings. A second stage at the inverter DC input is common when the DC run is long, so a surge is clamped at both ends of the cable.
Q: What IP rating does a combiner box need?
A: It follows the mounting and exposure. An outdoor rooftop box needs a higher rating than an indoor cabinet, and the internal space must fit the devices plus their leads and glands. The NXW1-3/5 IP65 enclosures are the confirmed housing family for a small outdoor shell.
Q: Is certification given for the whole box or for the parts?
A: For the parts, per exact ordering code. We do not issue a box-level certificate; each device inside carries its own document, stated for the code being quoted.
What to send us for a quotation
Number of strings and string Isc · array maximum system voltage · fused or breaker-fed · earthing arrangement · isolation requirement · monitoring or metering requirement · mounting (wall or pole) and exposure · destination country · quantity. You get unit price, packing data and the certificate document for each exact ordering code. Request a quotation.
Related: DC MCB for solar PV: 250 / 500 / 1000 V · DC SPD for solar PV · SPD and isolators · Boards and enclosures · DIN-rail energy meter selection · Mixed container consolidation