General information on Q3 string boxes and FAQs

What is a string box?

Our string boxes provide a high level of safety even during the installation and ensure a clean and clear wiring of the PV modules on the roof or in the open field. Multiple strings often must be connected parallell in order to transport a suitable electric power at a reasonable system voltage towards the inverter. The several strings are connected directly to the stringbox nearby the modules. Only two wires (plus and minus) connect the stringbox to the inverter.

We offer different types of string boxes. We will find the right configuration for your needs.

String fuse of diode?

In parallel-connected strings reverse currents of the other strings can occur at a defective or shaded module. This can reduce the yield and damage other modules. To prevent such incidents Q3 provides variants with diodes and string fuses.

String fuse

Fuses have relatively low power consumption and provide excellent protection in case of fault currents. If the fuse blows, it must be changed after the cause has been resolved. Until then, the string falls out completely. Q3 uses exclusively photovoltaic-approved fuses for a high level of security.


Diodes block from the beginning all types of reverse current and need not be replaced. Their power consumption at a threshold voltage of less than 1V is a little higher than that of fuses. We recommend diodes up to an Isc of 2A, i.e. usually in thin-film modules. In addition, fuses should be used.


Overvoltage protection

The correct selection of overvoltage protection is not always easy. Our experts gladly advice you, whether and what type of overvoltage protection is useful.

Circuit Breakers

DC circuit breakers are mandatory between inverter and module field and serve as an additional disconnection device in case of emergencies or maintenance.

Integrated Monitoring Systems

A monitoring systems provides an optimal yield of the PV plant. With our string-based currend measurement we offer an ideal monitoring fo all types of PV plants.

An overview of the most important features:

Our Connection Technology

Stringbox Simple

Cost-effective and light-weight string box with 2 up to 5 inputs for small crystalline modules and thin-film installations.

Stringbox Easy 3G

Compact and lightweight string box for small to medium-sized string combinations and thin-film systems of all types up to 18 inputs.

Easy Duo/Trio Channel

String box due to the electrically isolated PCBs which two oder three different MPP trackers or inverters can be operated with a single box.

Stringbox BIG

Generator connection box for large systems of the order of megawatts, openfield plants, large roofmounted systems, e.g. on factory buildings.


Customized AC Box for connecting up to 20 inverters project example REC Romania.


Further examples regarding our customized connection technology including pictures.

General information

What is a string box? Usage of fuses or diodes? What about monitoring, OVP, ...???