FAQ PV Firefighter Switches | Frequently Asked Questions

No, there is no general nationwide requirement to install firefighter switches. Whether a firefighter switch is required depends on the building type, system size, intended use, local building regulations and the interpretation of authorities and fire services. In many projects, the requirement results from the fire protection concept or project-specific specifications.

The decision is based on the interaction between system planning, fire protection concepts and official requirements. Relevant stakeholders may include building authorities, fire protection consultants and local fire brigades. System planners and operators share responsibility for implementing an appropriate level of risk mitigation.

Relevant requirements can be found in various standards and technical guidelines, including DIN VDE 0100-712, VDE-AR-E 2100-712 and recommendations issued by fire services. For the switching devices themselves, IEC 60947-3 is particularly important, as it defines requirements for safe isolation and switching functions.

Even after disconnecting the AC side, the DC cables between the PV generator and the inverter remain energized whenever sunlight is present. These DC voltages cannot be eliminated by simply disconnecting the grid and may present an electrical hazard during firefighting operations or maintenance work.

No. PV modules continue to generate voltage whenever exposed to light. However, a firefighter switch significantly reduces the hazardous area by disconnecting the DC circuits outside the generator field.

With string-level shutdown, several modules are disconnected together as one string. This approach is considered technically robust, economical and practical, particularly for commercial and industrial PV systems.

Module-level shutdown allows isolation of individual modules but requires additional electronics, increases system complexity and typically results in higher costs.

Galvanic isolation means the complete electrical separation of both active conductors (+ and −) of a PV string using a mechanical switching device.

Unlike electronic or grid-dependent shutdown concepts, galvanic isolation leaves no conductive connection between the PV generator and the downstream DC cabling after activation.

The QFire firefighter switch performs this disconnection directly within the switch box on the DC side, ensuring that hazardous DC voltages are no longer routed into the building during an emergency.

Galvanic isolation is widely regarded as the safest form of DC shutdown because it physically interrupts all active conductors of the PV string. The shutdown function remains effective regardless of grid conditions, communication signals or the operational status of other system components.

This provides reliable protection during fires, power outages or cable damage and complies with IEC / DIN EN 60947-3 requirements.

In a fail-safe system, the firefighter switch remains active only while control voltage is present. If the control voltage is lost due to a power failure or cable interruption, the system automatically disconnects the PV strings. When control voltage returns, the system can automatically resume operation.

QFire LITE is a standardized solution for DC string disconnection with a simple and defined shutdown mechanism directly within the switch box. It is available for 2 or 4 PV strings, with or without integrated surge protection.

QFire BIG provides additional functionality through a central control box, including status indication, external control stations and fire alarm system integration. The system is scalable and available for up to 24 PV strings per switch box. Optional surge protection and string fuses can be integrated according to project requirements.

Yes. QFire Cluster technology allows multiple PV generator fields or roof sections to be monitored and disconnected simultaneously. Individual strings are coordinated through the central QFire control logic and disconnected together when required.

This concept is particularly beneficial for large industrial sites, complex building structures, multiple fire compartments or extensive rooftop installations.

Yes. QFire BIG can be integrated into a fire alarm system (FAS). The control box enables automatic shutdown activation in accordance with the project’s fire protection concept and operational requirements.

Yes. QFire BIG supports multiple external control devices, including emergency stop buttons and key-operated switches. All shutdown commands are processed centrally through the control logic.

QFire is developed and manufactured in Germany. For many system operators, planners and public-sector clients, local manufacturing is an important factor regarding product quality, technical documentation, traceability and long-term product availability.

Yes. QFire is suitable for retrofitting existing PV installations. The firefighter switch is integrated into the DC circuit between the PV modules and the inverter. Particularly with QFire BIG, the system can be adapted to existing site conditions through project-specific engineering.

Permissible cable lengths depend on the project design, conductor cross-sections and electrical system parameters. These factors are evaluated during the planning phase to ensure reliable operation.

For QFire BIG systems, the control box is typically installed centrally, usually close to the inverter. This provides a convenient location for operation, monitoring and integration with external systems.

QFire switch boxes are installed close to the PV generator field, typically at the roof entry point where DC cables enter the building.

This arrangement minimizes the length of energized DC cables inside the building and improves safety during maintenance work and emergency situations.

QFire uses high-performance electrical relays to disconnect the DC strings. Unlike purely mechanical switching concepts, this approach enables reliable and arc-free string disconnection under photovoltaic operating conditions.

Once activated, the QFire firefighter switch galvanically disconnects all connected DC strings. The shutdown process takes place inside the switch boxes and significantly reduces the hazardous area outside the PV generator field.

Yes. When using the fail-safe principle, the system automatically returns to operation once the control voltage is restored and no shutdown condition remains active.

No manual intervention is required under normal operating conditions.

Many shutdown solutions available on the market require a manual reset directly at the modules or switch boxes after activation. This often involves roof access and opening enclosures.

Depending on the system design, QFire supports automatic recommissioning, reducing downtime and minimizing maintenance effort.

Firefighter switches generally require very little maintenance. However, as part of regular PV system inspections, visual inspections and functional testing should be carried out, particularly in safety-critical applications.

From a technical perspective, it is recommended to perform a functional shutdown test at least once per year.

A single QFire switch box can support up to 12 MPPTs and up to 24 PV strings.

By using additional switch boxes, larger systems can be implemented. QFire systems are fully scalable and can be adapted to larger commercial and industrial PV installations.

No. QFire BIG is not limited to a fixed system size. Thanks to its modular architecture and project-specific design, the system can be expanded step by step to match almost any photovoltaic project.

QFire uses genuine Stäubli MC4-EVO 2 connectors as standard.

Upon request, the system can also be supplied with:

• Amphenol connectors
• Phoenix Contact SUNCLIX connectors
• Terminal connection technology

This allows QFire to comply with existing project standards and customer requirements.

In multi-storey buildings, the system is typically controlled through a central AC supply. With QFire LITE, this AC voltage is looped through all floors.

If the AC supply fails during a fire or emergency, all connected firefighter switches automatically disconnect and galvanically isolate the PV strings. This minimizes energized DC cable lengths within the building and improves safety for emergency responders.