QCM-511706 – PV Field Combiner Box 8 Strings IP66
Photovoltaic string combiner box QCM-511706 for 8 DC strings with switch-disconnector fuse holders per string, Class II DC surge arrester and IP66 enclosure. Made in Italy by MR WATT / SecSun. Ideal for industrial and commercial PV systems. Dimensions: 510 × 720 × 250 mm — 5 kg.
The QCM-511706 is the MR WATT / SecSun photovoltaic field combiner box for systems with 8 DC strings in parallel. Positioned between the PV array and the inverter, it combines and protects the strings against overcurrents, short circuits and overvoltages before conversion to alternating current. The IP66 enclosure makes it suitable for outdoor installations on structures, canopies, industrial warehouses and ground-mounted systems, even in environments with dust, rain and direct water jets.
Role of the field combiner box in PV systems
In medium and large photovoltaic systems, panel strings are not connected directly to the inverter but first pass through a field combiner box (or string box). This component performs three essential functions:
- Combining: gathers the currents of multiple strings into a single output cable to the inverter or MPPT
- Protection: each string is individually protected by switch-disconnector fuse holders that isolate faults without stopping the entire system
- Surge protection: the Class II DC surge protective device protects the inverter and wiring from lightning and induced transients
QCM-511706 technical specifications
| Product code | QCM-511706 |
| Manufacturer | MR WATT / SecSun – made in Italy |
| Number of strings (inputs) | 8 |
| String protection type | Switch-disconnector fuse holder with DC fuses |
| Surge protective device | DC Class II |
| Protection rating | IP66 |
| Maximum DC voltage | 1000 V DC (or 1500 V DC on request) |
| Reference standards | CEI EN 61439-1/2, IEC 60269-6 |
| Dimensions (WxHxD) | 510 × 720 × 250 mm |
| Weight | 5 kg |
| Installation | Outdoor / indoor, wall or structure |
| Typical application | Commercial and industrial PV systems 20–100 kWp |
When is the 8-string QCM-511706 used?
The choice of the number of strings depends on the inverter and PV array configuration. The QCM-511706 with 8 inputs is suitable for systems with power typically between 20 and 100 kWp, where multiple panel strings converge to a single inverter MPPT or to the DC section of a combiner panel. It is the standard solution for systems on warehouses with multiple roof pitches, canopy structures, agrivoltaic systems and medium-size ground-mounted installations.
Available versions in the QCM range
MR WATT offers the full range of SecSun field combiner boxes for any system configuration:
- QCM-2 strings: for small systems or dedicated MPPTs
- QCM-4 strings: intermediate residential/commercial configuration
- QCM-511706 – 8 strings: ideal for mid-size commercial and industrial
- QCM-12/16 strings: for large-scale systems
- Custom configurations: available on request for number of strings, voltage (1000/1500V DC) and protection type
Frequently asked questions
Is a field combiner box always necessary in a photovoltaic system?
No, not always. Inverters with multiple dedicated MPPT inputs can accept strings directly without an intermediate field combiner box. The field combiner box becomes necessary when the number of strings exceeds the available inverter inputs, or when strings converge on a single MPPT and the CEI 64-8 standard requires individual protection of each string to prevent fault currents. For systems from 20 kWp upwards with centralized inverters or large multi-MPPT units, the field combiner box is in practice almost always present.
Is the QCM-511706 already internally wired or does it need to be assembled on site?
The QCM-511706 is supplied pre-assembled with fuse holders, DC fuses and surge protective device already installed. On site, you only need to connect the cables coming from the strings to the panel inputs and the output cable to the inverter, following the system single-line diagram. No internal assembly is required.
Is the IP66 rating sufficient for outdoor installation in coastal or industrial areas?
IP66 guarantees complete protection against dust and against powerful water jets from any direction, making it suitable for outdoor installation in adverse weather conditions. For environments with a high presence of salt spray (marine coastal areas) or aggressive chemical agents (industrial areas), it is advisable to request enclosure versions with reinforced anti-corrosion treatment. Contact MR WATT to evaluate the most suitable solution.
Can I use the QCM-511706 with any inverter brand?
Yes. The field combiner box acts exclusively on the DC side of the system, before the inverter. It is therefore compatible with any photovoltaic inverter that accepts DC input: Huawei SUN2000, SMA Tripower, Fronius Symo, Solax X3, Sungrow SG, GoodWe, Growatt and all others. The only required check concerns the system maximum DC voltage (1000V or 1500V) and the maximum current per string.
Is there a version of the box with more or fewer than 8 strings?
Yes. MR WATT manufactures the entire SecSun QCM range with configurations from 2 to 16 strings, with the possibility of customized versions for specific requirements (1500V DC voltage, Class I+II surge protective devices, main isolator, etc.). Contact MR WATT to receive a quotation for the configuration suitable for your system.
