Connection Technology for PV Power Plants

Connection Technology Generator Junction Box String Boxes



We build your box!


Q3 string boxes (generator connection box) are individually manufactured according to your requirements from one copy upwards and vary in their equipment (type of housing, number of inputs and outputs, fuse/diode...).

Optionally we build your box with (remote triggerable) DC circuit breaker, overvoltage protection (T1+T2/T2), string current measurement, voltage measurement and data transmission. Thus, the appropriate technology can be selected for each PV system variant.

  • competent and partnership-based support during the planning phase
  • simple and quick installation
  • PV-optimised components
  • customer-specific = cost/benefit optimised
  • suitable for every type of module


String Boxes and Generator Junction Boxes from Q3

Our string boxes provide a high degree of safety already during installation and guarantee a clean and clear wiring (stringing) of PV modules on the roof or in open space. Often several strings have to be connected in parallel to transport suitable power to the inverter at reasonable system voltages. The individual strings are connected directly to the modules in the String Box and are connected to the inverter input with only two wires (plus and minus).



Stringbox Simple

Protection of the Modules and Yield Reliability

Back currents in case of shaded or defective modules are prevented, thus ensuring a long service life of the system. In the case of a defective or shaded module, if strings are connected in parallel, currents from the other strings can flow backwards through the affected string, thus reducing the yield and also damaging the other modules. To prevent this we offer variants with diodes and string fuses. We will be happy to advise you on this!

Stringbox Simple

Easy installation - no need to open the housing

Special enclosures approved and suitable for the application make installation simple and safe. Clever connection technology always ensures the quickest and simplest installation variant!

Stringbox Simple

Savings in cabling costs

Through the project-accompanying planning, large quantities of copper and significant installation costs can be saved.

Stringbox Simple

Individual assembly

Your box is equipped with overvoltage protection, fuses, blocking diodes, switch disconnectors and monitoring systems as required.

Stringbox Simple

String fuse or diode?

Reverse currents through the modules must be prevented. This is achieved by diodes or fuses. Both variants have their charm:

fuses have a relatively low power consumption and offer excellent protection against leakage currents. If the fuse blows, it must be replaced after the cause has been clarified. Until then the string will fail completely. Q3 only uses fuses approved for PV systems for a high degree of safety.

diodes block any kind of reverse current from the outset and do not need to be replaced. Their power consumption is slightly higher than that of the fuses at a threshold voltage of less than 1 Volt. We recommend diodes up to an Isc of 2 A, i.e. as a rule for thin-film modules. Beyond that, fuses should be used.

Stringbox Simple

Overvoltage protection

The right choice of surge protection components protects the critical components in an emergency. The correct selection of surge protection is not always easy. Our experts will be pleased to advise you on whether and what type of surge protection is appropriate.

Stringbox Simple

Circuit breaker

DC disconnectors are mandatory between the inverter and the module field and serve as an additional disconnecting device in emergencies, for repairs or maintenance work.

Stringbox Simple

Integrated monitoring systems

Perfect system monitoring ensures that the system always produces the optimum yield. With a current measurement on a string basis, this can be provided for all types of systems.

Stringbox Simple

Single string current monitoring

Optionally we offer a single string current monitoring. Here the total voltage is measured as well as the current flow through each individual string. In addition, the switch position of the DC isolator and whether the OSS has tripped can be recorded. The power supply of the monitoring is done by drawing energy from the strings. This means that there is no need to connect an external power supply or to wire the communication in the field.

Our portfolio in the field of connection technology, string boxes, generator connection boxes


Stringbox Simple

extremely low structure, up to 6 inputs

String Box Easy

extremely compact, up to 18 inputs


Stringbox with galvanically separated circuit boards

Stringbox BIG

Generator junction box for large plants/parks

AC sub-distribution

customer-specific variant with OVP T1+T2

Special Boxes

cost-optimised - benefit-optimised

Experience, for your safety!

Since 2010 we have been building string boxes and GAKs as well as AC combiners in all variants and for the most diverse applications, especially in the PV sector. From simple DC junction boxes to complex junction boxes for PV power plants with several MW output, a large number of plants worldwide are equipped with the proven technology of Q3. This experience is to your advantage - do not make any compromises - as the subject of connection technology is also a safety issue in PV applications with high currents and voltages in sometimes complicated installation situations.


Highest quality

We only use components from renowned manufacturers. The dimensions of the individual terminals, assemblies, plugs etc. are precisely calculated and proven in use for the PV sector.