String combiner in a solar park

String combiner for photovoltaic systems Custom solution concepts

Specialists who design and build photovoltaic systems face the challenge of achieving maximum availability and performance of photovoltaic systems. The important factors here are collecting and distributing string currents, protecting the individual modules against damage from lightning and overvoltage, and monitoring the performance of the system.

String combiner boxes (SCBs) from Phoenix Contact meet these requirements in a space-saving housing. Our monitoring system for photovoltaic string currents allows you to respond immediately to malfunctions and power losses, even when individual strings fail.

Solar park with two people

Application for string combiner boxes


The string combiner box collects and distributes the string currents from the solar panels. In addition, the string combiner box monitors the system performance and protects the individual modules against damage from overvoltage. Special applications include floating photovoltaic systems. Due to their location at sea or on inland bodies of water, they place very particular demands on the string combiner boxes.

Solution: String combiner boxes for photovoltaic systems

Connection technology for photovoltaics
Lightning and surge protection for photovoltaic systems
Monitoring of photovoltaic systems at string level
Compact DC/DC converters with basic functionality for photovoltaics
DC bus cables in photovoltaic systems
Connection technology for photovoltaics

An extensive product portfolio featuring a variety of terminal blocks provides the right solution for any application. Fuse terminal blocks are ideal for protecting individual strings against reverse currents.

Diode terminal blocks are specifically designed for the use of photovoltaic thin film, while the hybrid terminal block merges up to four strings without additional wiring effort.

Lightning and surge protection for photovoltaic systems

Due to their size and exposed location, ground-mounted photovoltaic systems are particularly at risk from lightning currents and overvoltages.

Take preventive action and significantly increase the availability of your system with lightning current and surge protective devices from Phoenix Contact. The protective devices meet the EN50539-11 and UL 1449 3rd edition standards for surge protection in photovoltaic installations and are KEMA-certified.

Monitoring of photovoltaic systems at string level

Using Hall sensors, the current measuring module determines the parameters of your photovoltaic systems on a contact-free basis and forwards them to the communication module. Four- and eight-channel versions are available.

You can measure DC voltages up to 1500 V with the voltage measuring module. The module is suitable for measurement in both grounded and isolated photovoltaic systems.

Compact DC/DC converters with basic functionality for photovoltaics

The DC/DC converter with basic functionality for photovoltaics allows you to supply your string combiner boxes directly from the ground-mounted system.

As a result, you save on installation costs and increase system efficiency. Due to its compact design and high efficiency, the DC/DC converter can also be used in small control boxes.

DC bus cables in photovoltaic systems

DC bus cables of up to 600 A are monitored with the universal AC/DC current transducers. This means that the conductor to be monitored does not have to be interrupted.

Current transformers make it possible to convert alternating currents for different transmission ratios. Downstream energy measuring devices can be used to record and display parameters directly in the control cabinet.

Your advantages

  • Application-oriented analysis and consultation
  • Standardized tests in an accredited laboratory
  • Reliability and durability with a temperature-optimized design
  • Lower installation and maintenance costs and flexible networking with wireless communication

Wireless networking of serial interfaces

Data from string combiner boxes is output via serial RS-485 interfaces and transmitted wirelessly to the central park management system. Our proven wireless technology enables reliable, interference-free communication over a distance of up to 500 m with up to 250 string combiner boxes. Since our wireless system allows mesh networks to be set up, the devices can communicate with each other via repeater and server stations.

Floating photovoltaic systems

Special application examples: Floating photovoltaic system

Examples of special applications

To keep the cabling effort as low as possible, the use of wireless modules is highly recommended in floating photovoltaic systems in particular. Phoenix Contact provides salt-water resistant SCBs with special strain relief for the solar cables in the event of strong swells.

Our wireless technology is also recommended for retrofitting monitoring systems and existing photovoltaic systems. There is no need for any of the major excavation work involved in laying new cables, which keeps the costs for the retrofitting manageable.

Monitoring photovoltaic strings

The measuring module can be used to measure up to eight direct currents and one DC voltage value at the same time. The complete system allows you to operate eight measuring modules on one communication module. The 2-conductor communication cable is used to supply the measuring modules with energy. An additional power supply is not necessary. The universal current transducer allows measurement of AC and DC currents on bus cables.

Structure of photovoltaic string monitoring

From string to bus cables, Phoenix Contact ensures the reliable monitoring of photovoltaic systems

Employees talking about string combiners in the solar sector

Control cabinet solutions for every customer requirement

Development of the string combiner boxes

During preliminary development clarification, all divisions work closely with our customers to implement the desired requirements in the best way possible.

Specific challenges are identified at an early stage. As a result, the development process is designed to be target-oriented and efficient. Once the initial clarification phase is complete, the design phase gets underway.

During this phase, prototypes are built and undergo a specific testing procedure. The findings are used to further optimize the solution.

SCB test method

The temperature-optimized control cabinet design excludes potential failure due to thermal overload

Testing procedures

The prototypes are subjected to electrical and mechanical testing in our in-house laboratories. The tests ensure that the solutions operate without errors in the intended installation environments.

Problems such as possible hotspots are detected via a thermographic test in the in-house laboratory. The results are used to define the optimal layout of components in the string combiner box. This eliminates failure due to thermal overload.

SCB Compact and SCB Next Generation string combiner boxes

Two intelligent solution concepts: SCB with string fuse outside the control box for 32 strings and SCB with standard string fuse for 20 strings.

Production of string combiner boxes

Following successful completion of all relevant tests in the development phase, production of the item is given the go-ahead. The components are manufactured in a one-piece flow to ensure that each individual step is efficiently implemented. This makes it possible to respond quickly and flexibly to changing designs and lot sizes. The required quality assurance information can be viewed at a glance, which ensures that the production and assembly process runs smoothly.

Quality control in production
In the production line, tools are used that allow all items to be produced with repeat accuracy. The use of screwdrivers with torque control ensures reliable and safe connections. This ensures the consistent quality of each individual string combiner box. In the final production step, final testing takes place in accordance with IEC 61439. Finally, a test report is generated. All switchgear and controlgear assemblies and the electronic components they contain have serial numbers that make them uniquely identifiable at any time.