PV combiner box for Huawei 330KTL: 28 strings and firefighter switch in one enclosure
Custom DC connection and protection solution for a utility-scale PV system in Hörselgau
This PV combiner box for Huawei 330KTL was developed to route, protect and remotely disconnect all 28 PV strings within a single enclosure: for a PV installation in Hörselgau, Germany, the DC architecture was designed specifically around the input configuration of the Huawei SUN2000-330KTL inverter.
The original requirement was straightforward. In previous projects using this inverter type, two separate PV combiner or connection boxes had been required per inverter. For this project, the objective was to accommodate all 28 PV strings in a single enclosure wherever technically feasible.
Q3 ENERGIE therefore developed a project-specific version based on the QFire BIG firefighter switch. The solution combines 1:1 routing of all 28 strings with string fusing, DC surge protection and remotely controlled DC disconnection.
Five of these units were installed in Hörselgau.
Project implementation by Kintlein & Ose GmbH & Co. KG ⚡☀️
Huawei 330KTL
28 Strings
QFire BIG
| Project data | Design |
|---|---|
| Application | Ground-mounted PV system |
| Location | Hörselgau, Thuringia, Germany |
| Inverter | Huawei SUN2000-330KTL |
| Technology | Project-specific QFire BIG firefighter switch |
| PV strings per box | 28 |
| Total string circuits | 140 |
| MPP trackers per inverter | 6 |
| System voltage | Up to 1,500 V DC |
| QFire switching current | up to 20 A Isc per string |
| String routing | 28 inputs / 28 outputs, 1:1 |
| String fusing | Positive conductor, project-specific 30 A |
| Surge protection | 6 × Type 1+2 DC SPD per box, with remote signalling contact |
| Enclosure | Sheet steel, IP66 |
| Special Features | QFire BIG custom configuration for 28 strings |
The challenge: PV combiner box for Huawei 330KTL with 28 PV inputs in one box
The Huawei SUN2000-330KTL features six independent MPP trackers and a total of 28 PV inputs. The inputs are distributed across the six MPP trackers in a 4/5/5/4/5/5 configuration.
For the DC connection system, this results in an unusually high number of individual string circuits to be routed to each inverter.
Using two separate enclosures is technically possible, but it increases space requirements as well as installation and cabling effort. The objective in Hörselgau was therefore to develop a solution in which all 28 strings assigned to one inverter could be routed through a single enclosure.
he result was not a standard product configuration, but a project-specific design for commercial, industrial and utility-scale PV applications.
QFire BIG custom configuration for 28 PV strings in one PV combiner box for Huawei 330KTL
The standard QFire BIG range is designed for switch boxes with up to 24 PV strings. For this project, the system architecture was extended to provide 28 inputs and 28 outputs.
Each PV string remains individually routed from the PV generator to the corresponding inverter input. The strings are not combined within the enclosure.
This is an important distinction. Although the unit performs functions normally associated with a PV combiner or generator connection box, the 28 string circuits remain separate throughout the enclosure. This preserves the required allocation between each PV string and the inverter’s individual inputs and MPP trackers.
At the same time, the enclosure integrates several functions of the DC infrastructure:
- string fusing on the positive conductor
- Type 1+2 DC surge protection for all six MPP trackers
- 1:1 routing of all 28 PV strings
- remotely controlled double-pole disconnection of the PV strings via QFire
- project-specific connection configuration to the inverter
The QFire switching system disconnects both the positive and negative conductors of the relevant PV strings. The underlying QFire BIG technology is designed for systems up to 1,500 V DC and 20 A Isc per string in accordance with IEC 60947-3.
Six MPP trackers – six surge protective devices
The surge protection concept was also designed around the inverter architecture rather than simply around the total number of strings.
The Huawei 330KTL operates with six MPP trackers. Accordingly, each enclosure was equipped with six Type 1+2 DC SPDs with remote signalling contacts.
This allows the surge protection architecture to follow the electrical structure of the inverter. For EPCs and electrical designers, this is a key planning point: the total string count alone does not determine the configuration of a DC connection box. The allocation of those strings across the individual MPP trackers must also be taken into account.
Pre-assembled connection to the Huawei inverter
The connection concept was also adapted to the specific project requirements.
On the PV generator side, the standard Q3 connection configuration was used. On the inverter side, the five Hörselgau units were supplied with pre-assembled 1.2-metre PV cables fitted with Amphenol H4 connectors.
This meant that the interface between the DC connection box and the inverter could already be incorporated during manufacturing.
For larger PV projects, this approach reduces the number of adaptations that would otherwise have to be carried out on site. Connector type, cable length, polarity and string allocation can all be defined during the engineering phase of the enclosure.
One inverter – one box
The five installed units demonstrate one of the principal advantages of project-specific DC connection technology:
the enclosure is designed around the PV system architecture – not the other way round.
Each PV combiner box for Huawei 330KTL in Hörselgau is assigned one Q3 enclosure with 28 separate string circuits.
Across the five units, a total of 140 PV strings can therefore be routed, protected and, where required, disconnected on the DC side.
Clear identification of each enclosure also ensures an unambiguous assignment between the DC connection box and the relevant inverter.
Weather-protected installation for reliable operation of the PV combiner box for Huawei 330KTL
The project photographs show another important aspect of the installation: the enclosures were mounted beneath dedicated protective canopies.
Even where an enclosure provides a high IP rating, permanent outdoor equipment should not be exposed unnecessarily to direct solar radiation or weather. For QFire systems, a shaded and weather-protected installation location is therefore specified.
The Hörselgau installation follows this principle consistently. At the same time, the cable entry areas remain accessible and the cable routes are clearly structured.
A robust PV system is not defined solely by the electrical components used. Mounting location, cable routing, shading, accessibility and maintainability are all part of the engineering concept.
Delivered in cooperation with Kintlein & Ose
The project PV combiner box for Huawei 330KTL was implemented together with Kintlein & Ose GmbH & Co. KG, an experienced EPC and project partner for large-scale PV installations.
The project illustrates how custom DC connection technology should be developed: inverter architecture, string allocation, protection concept, interfaces and installation requirements are considered together before the enclosure is engineered.
Q3. The Box Makers.
What EPCs and designers can take from this project
An inverter with 28 individual PV inputs does not automatically require two separate DC connection boxes.
The key is to consider the DC infrastructure during the engineering phase and to coordinate it with:
■ the inverter architecture
■ the MPPT configuration
■ the number and allocation of PV strings
■ the protection concept
■ the required shutdown philosophy
■ the physical installation environment
For utility-scale and commercial PV systems, several functions can often be integrated within one enclosure: string routing, string fusing, surge protection and – where required by the fire protection or shutdown concept – remotely controlled DC disconnection.
The appropriate solution therefore does not necessarily come from a catalogue.
Sometimes the enclosure simply has to be designed around the system.
Frequently asked questions about PV combiner box for Huawei 330KTL
Can all 28 strings of a Huawei 330KTL be routed through one DC connection box?
Yes. For this project, Q3 developed a custom solution with 28 separate inputs and 28 separate outputs. This allows all PV inputs of one Huawei 330KTL to be routed through a single enclosure without combining the individual string circuits.
How many MPP trackers does the Huawei SUN2000-330KTL have?
The Huawei SUN2000-330KTL has six MPP trackers and a total of 28 PV inputs. The input allocation is 4/5/5/4/5/5.
Can a PV combiner box and firefighter switch be integrated in the same enclosure?
Yes. Depending on the project, DC connection functions such as string fusing and surge protection can be integrated together with a QFire switching unit in one project-specific enclosure.
This avoids the need for an additional separate QFire switch box.
Does every PV system using a Huawei 330KTL require a firefighter switch?
No. The requirement for additional DC disconnection is not determined by the inverter model alone.
Relevant factors include the overall system architecture, DC cable routing, the fire protection concept and any project-specific or authority requirements.
Plan the DC connection solution for your PV project
Are you using the Huawei SUN2000-330KTL or another inverter with a complex string and MPPT architecture?
Q3 ENERGIE develops PV combiner boxes and DC connection solutions designed around the actual system – from standard configurations to project-specific enclosures with surge protection, string fusing and integrated QFire DC disconnection.
Q3. The Box Makers.