Connection technology for PV power plants

Connection technology Generator connection box String boxes



We build your box!


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

We can optionally build your box with a (remotely triggered) DC circuit breaker, overvoltage protection (T1+T2/T2), string current measurement, voltage measurement and data transmission. This means that the right technology can be selected for every PV system variant.

  • Competent and cooperative support during planning
  • Quick and easy installation
  • PV-optimized components
  • Customer-specific = cost/benefit-optimized
  • Suitable for every module type

String boxes and generator connection box from Q3

Our string boxes ensure a high level of safety right from the installation stage and guarantee clean and clear wiring (stringing) of PV modules on the roof or in the open field. Several strings often have to be connected in parallel in order 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 connected to the inverter input with just two cables (plus and minus).



Stringbox Simple

Module protection and yield security

Reverse currents in the event of shaded or defective modules are prevented, ensuring a long service life for the system. If a module is defective or shaded, currents from the other strings connected in parallel can flow backwards through the affected string and thus reduce the yield and also damage the other modules. To prevent this, we offer variants with diodes and string fuses. We will be happy to advise you!

Stringbox Simple

Simple installation - no need to open the housing

Enclosures specially approved and suitable for the application make installation simple and safe. Clever connection technology always ensures the quickest and simplest installation option!

Stringbox Simple

Savings in cabling costs

Thanks to project-related planning, large quantities of copper and significant installation costs can be saved.

Stringbox Simple

Individual assembly

Depending on your requirements, your box will be equipped with overvoltage protection, fuses, blocking diodes, load-break switches and monitoring systems.

Stringbox Simple

String fuse or diode?

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

Fuses have a relatively low power consumption and offer excellent protection against fault currents. If the fuse blows, it must be replaced once the cause has been clarified. Until then, the line will fail completely. Q3 only uses fuses approved for PV systems to ensure a high level of safety.

Diodes block all types of reverse currents from the outset and do not need to be replaced. At a threshold voltage of less than 1 volt, their power consumption is slightly higher than that of the fuses. We recommend diodes up to an Isc of 2 A, i.e. usually for thin-film modules. Fuses should also be used.

Stringbox Simple

Overvoltage protection

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

Stringbox Simple


DC disconnectors are absolutely essential between the inverter and the module array 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 an optimum yield. With current measurement on a string basis, this can be provided for all system types.

Stringbox Simple

Single string current monitoring

We offer optional single-string current monitoring. The total voltage is measured here, as well as the current flow through each individual string. In addition, the switch position of the DC isolating switch and whether the OSS has tripped can be recorded. Power is supplied to the monitoring system 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 (GAK)


Stringbox Simple

Extremely low profile, up to 6 inputs

Stringbox Easy

Extremely compact, up to 18 inputs

Duo/Trio channel

Stringbox with galvanically isolated circuit boards

Stringbox BIG

Generator connection box for large systems/parks

AC sub-distribution board

Customer-specific variant with ÜSS T1+T2

Special boxes

cost-optimized - benefit-optimized

Generator connection box "large"

with overvoltage protection

Generator connection box "small"

with overvoltage protection

Experience, for your safety!

We have been building string boxes and GAKs as well as AC combiners in all variants and for a wide range of applications, especially in the PV sector, since 2010. From simple DC disconnection boxes to complex junction boxes for PV power plants with outputs of several MW, a large number of systems worldwide are equipped with Q3's proven technology. You will benefit from this experience - do not make any compromises - as the topic of connection technology in PV applications with high currents and voltages in sometimes complicated installation situations is also a safety issue.

Highest quality

We only use components from reputable manufacturers. The dimensions of the individual terminals, assemblies, connectors etc. are precisely calculated and tried and tested for use in the PV sector.