QFire BIG PV Firefighter Safety Switch for Large PV Systems
Generator-side disconnection of multiple PV strings – project-specifically planned, with galvanic isolation according to IEC 60947-3.
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String-Level Remote DC Disconnection for Large PV Systems
QFire BIG is a string-based, remotely controllable DC disconnection solution for commercial and industrial PV systems designed in accordance with IEC requirements.
The system is designed for rooftop PV systems, industrial buildings, logistics roofs and complex photovoltaic installations where multiple PV strings, long DC cable routes or several PV generator fields need to be shut down safely.
The QFire BIG switch boxes are installed close to the PV generator and galvanically isolate the connected PV strings in accordance with IEC 60947-3. Depending on the project, up to 24 PV strings can be handled in a single switch box. The system is configured to suit the specific installation – taking into account the number of strings, system voltage, string current, roof structure, cable routing and the required shutdown concept.
In addition, QFire BIG can be integrated into an AC-side shutdown concept on a project-specific basis. Via the status contact of the QFire control box, external components such as grid and system protection, inverter enable signals or on-site contactor control systems can be triggered. This allows DC-side PV generator disconnection and AC-side shutdown logic to be planned together for large PV systems.
QFire BIG is not a module optimiser and not a conventional module-level rapid shutdown solution. Its focus is not on power optimisation at individual module level, but on safe DC string shutdown and PV generator disconnection for professional PV systems – for example in the event of fire, during maintenance work or for service operations.
Thanks to its central control box, project-specific DC switch boxes, optional cluster solution and external emergency-stop connection, QFire BIG can be flexibly integrated into a wide range of system concepts. The system is particularly suitable for:
QFire BIG At A Glance
| Application | Project-specific connection boxes |
| Function | DC string shutdown / PV generator disconnection |
| Isolation | Galvanic isolation according to IEC 60947-3 |
| System Voltage | Up to 1,500 V DC |
| String Current | Up to 20 A Isc per string |
| Number of Strings | Up to 24 PV strings per switch box |
| Extensions | Emergency stop, key switch, fire alarm system, status contact, SPD, fuses, cluster solution, integration into AC-side shutdown concepts |
Large Industrial and Commercial Roofs
Multiple Roof Areas
Expandable PV Projects
Multiple Inverters & MPP Trackers
Complex System Structures
Increased Safety Requirements
The modular system architecture is particularly suitable for complex roof structures, multiple generator fields, and large PV capacities with many strings. Depending on system size, switching units for 2 to 24 strings are available – with system voltages up to 1,500 V DC and up to 20 A per string.
For extensive sites, multiple QFire systems can be controlled together via the QFire Cluster Control Box. This allows central disconnection of multiple buildings or separate generator fields.
Surge protection, external emergency stop buttons, key switches, status contacts, and online monitoring via QFire.LIVE are optionally available.
QFire BIG is a firefighter switch for large PV systems with multiple generator fields, complex roof structures, and high safety requirements.
QFire BIG PV Firefighter Safety Switch in PV System Planning
Which PV firefighter switch is suitable for commercial PV systems?
In commercial and industrial PV systems, a simple DC disconnect switch at the inverter is often not sufficient, especially when long DC cable routes, multiple roof areas or specific requirements from the fire safety concept have to be considered. The key points are where the PV strings are disconnected, which voltages and currents are present, and how the shutdown should be triggered in an emergency.
QFire BIG is designed for exactly these types of systems. The switch box is installed close to the PV generator and disconnects the connected PV strings by galvanic isolation according to IEC 60947-3. This allows the DC cables from the switch box towards the inverter to be disconnected in a controlled way – manually via the control box, via external emergency stop or key switches, via a fire alarm system or, depending on the system design, AC-coupled in case of grid failure.
For planners and installers, the important point is this: QFire BIG is not treated as a standard off-the-shelf device, but is configured project-specifically according to the number of strings, roof structure, cable routing, protection concept and required accessories.
What is needed for DC string disconnection in large PV systems?
In large PV systems, DC string disconnection should be considered early in the planning phase. The most relevant factors are the maximum DC system voltage, the short-circuit current per string, the number of strings, the allocation to MPPTs, the cable routes from the PV generator to the inverter and the requirements from the fire safety concept.
QFire BIG is configured precisely for these conditions. Depending on the project, several strings can be combined in one switch box and disconnected close to the generator. Optional components such as surge protection, PV fuses, status contacts, external shutdown points or cluster solutions for multiple roof areas can be integrated.
The aim is not to place as many components as possible somewhere in the system, but to create a clear and serviceable DC structure: traceable string routing, a defined disconnection point, clear status indication and a solution that fits the actual PV system.
How can multiple PV strings be disconnected safely?
Multiple PV strings are best disconnected at the point where they are routed from the generator towards the building or inverter. This is exactly where QFire BIG is used. The switch box is installed close to the generator and disconnects the connected DC string cables by galvanic isolation.
Depending on the configuration, several PV strings can be handled in one QFire BIG switch box. This makes it possible to create a structured shutdown concept even for larger rooftop systems, without having to treat every single string with a separate standalone solution. Operation is carried out centrally via the control box or via integrated external shutdown points.
For large systems with several building sections or roof areas, the shutdown concept can also be planned using cluster technology. This keeps operation clear and manageable, even when the DC structure of the PV system is more complex.
Combining DC and AC shutdown in the system concept
In large PV systems, industrial projects and megawatt installations, the shutdown concept often has to be considered as a complete system. QFire BIG disconnects the PV strings on the DC side close to the generator by galvanic isolation according to IEC 60947-3. In addition, the status contact of the QFire control box can be used project-specifically to integrate external AC-side components – for example a grid and system protection relay, an inverter enable signal or a site-specific contactor control.
This is particularly relevant for large rooftop systems, installations with several inverters, hybrid systems with battery storage or projects with special requirements regarding fire safety, grid connection and operational safety.
More information on combined DC and AC-side shutdown can be found in our technical explanation of QFire PV generator disconnection.
Modular System Design of Generator Disconnection for Large PV Systems and Rooftop Installations
QFire BIG enables galvanic isolation of PV strings between the generator field and inverter. Typical components are:
Separation of control [2] and DC switch boxes [1]
Expandable through additional switch boxes
Integration of fire alarm system and/or external emergency stop button [3]
Central or cluster-based disconnection
The QFire BIG system has a modular design and consists of a central control box, optional cluster control boxes, and DC switch boxes for up to 24 strings per box. The switch boxes are custom-built and can optionally be equipped with surge protection and fuses.
Optional components are:
■ Fire alarm system connection
■ Integrated surge protection
■ Integrated fuses in positive and/or negative pole
■ External emergency stop button
■ Cluster technology for multiple roof areas
■ Online monitoring
■ Delay circuit (time-delayed disconnection of large systems)
In case of disconnection, all strings are galvanically isolated so that the lines from the installation location of the firefighter switch toward the inverter become de-energized.
This separation of control and switching function enables flexible adaptation to system size, roof structure, and safety requirements.
Galvanic Isolation of All DC Strings by the QFire BIG PV Firefighter Safety Switch
The QFire PV firefighter switch provides two-pole galvanic isolation of all connected PV strings in accordance with IEC 60947-3. In the event of activation, both the positive and negative conductors of each string are reliably disconnected from the inverter, ensuring maximum safety during fire incidents and emergency response.
Clear distinction from motor switch solutions
Two-pole disconnection of positive and negative conductors
Safe interruption of the DC connection
DC-side shutdown directly at string level instead of AC-side isolation only
Suitable for system voltages up to 1,500 V DC and string currents up to 20 A
Galvanic isolation completely interrupts the electrical connection between the PV generator and the inverter. After activation, the cables downstream of the QFire switching unit are de-energised. This principle significantly reduces DC-related hazards during fire emergencies and helps maximise safety for firefighters, emergency responders and service personnel.
This shutdown principle significantly improves safety during fire and emergency situations by reliably interrupting dangerous DC voltage. At the same time, galvanic isolation remains effective regardless of the PV system configuration, string length or the number of connected generator fields.
QFire BIG Firefighter Safety Switch: Control Box for Large PV Systems
Central Control and Coordinated Disconnection of PV Strings
The QFire control box operates with independent system logic. This ensures that the disconnection function remains clearly defined and reliably controllable even with complex system structures, multiple roof areas, or long cable runs.
The control box forms the central control element of the QFire BIG generator disconnection. It handles the complete evaluation logic of incoming control signals and coordinates the control of connected switch boxes. In case of triggering, the control box ensures defined, safe disconnection of all connected DC strings – regardless of number, distance, or system size.
Through the clear separation of control and DC switching function, the electrical structure remains clear and compliant with standards. The control box itself does not switch DC loads but functions as a higher-level logic and interface layer. This makes the system particularly suitable for larger and complex PV systems with multiple generator fields or future expansion requirements.
QFire BIG PV Firefighter Safety Switch:
Cluster Technology for Large PV Systems
Cluster technology enables central disconnection of multiple generator fields via a common control logic.
QFire BIG PV Firefighter Safety Switch: Cluster Control Box for Central Shutdown of Distributed Generator Fields
Additionally: Higher-Level, Star-Configured Disconnection Structure
For large and complex photovoltaic systems with multiple roof areas or generator fields, the cluster control box extends the QFire BIG system with a higher-level, star-configured disconnection structure.
The cluster control box supplements the functions of the QFire BIG generator disconnection for systems with multiple roof areas, halls, building sections, or widely distributed generator fields. It functions as a higher-level distribution and coordination unit and enables star-configured connection of multiple switch boxes or system segments.
The cluster structure allows even large and spatially complex PV systems to be shut down reliably and simultaneously. The shutdown logic remains clearly defined – regardless of the number of connected switch boxes or the overall size of the installation. This makes the QFire BIG firefighter switch system with cluster control box particularly suitable for industrial, commercial and logistics facilities, as well as for projects with future expansion requirements.
Triggering Methods and Interfaces
Plug + Play Installation
QFire BIG PV Firefighter Safety Switch For Modular DC Shutdown with Galvanic Isolation
For Safe Disconnection Up to 1,500 V DC / 20 A per String
The QFire BIG firefighter switch boxes provide galvanic isolation of the PV strings directly at the generator field. They form the central DC switching function of the system and ensure safe, standards-compliant disconnection of the connected strings during shutdown.
Through the modular design, the switch boxes can be flexibly adapted to different system structures – from small partial generators to large PV systems with multiple roof areas and high string counts.
Each switch box in the system provides galvanic isolation of the connected PV strings directly at the installation location.
How does the QFire BIG differ from Module Optimizers and Rapid Shutdown Systems?
QFire BIG is not a module optimizer solution and not a conventional module-level rapid shutdown solution. This distinction is important because these systems follow a different technical approach.
Module optimizers, microinverters and MLPE systems operate directly at the individual module or module string and are often associated with power optimization, monitoring or rapid shutdown. QFire BIG is designed differently: the system disconnects PV strings close to the generator via a switch box and is designed for commercial and industrial PV systems with multiple strings, clear cable routing and a defined shutdown concept.
The focus is not on module optimization, but on safe DC string disconnection and PV generator disconnection. QFire BIG disconnects the DC strings by galvanic isolation according to IEC 60947-3 and is integrated into the project-specific system planning.
QFire BIG PV Firefighter Safety Switch: Project-Specific Instead of Standard Solution
The QFire BIG switch boxes are designed, planned, and manufactured project-specifically. String count, connection technology, protective components, enclosure sizes, and interfaces are individually tailored to the respective system structure.
This creates not an off-the-shelf standard solution, but a technically sound, standards-compliant, and future-proof disconnection solution – Made in Germany.
Number of strings
■ Switch boxes from 2 to 24 PV strings
■ Flexible string reductions between input and output
Connectors and Connection Variants
■ Standard: MC4-Evo2 from Stäubli
■ Alternatively H4, Sunclix, or terminal technology possible
DC surge protection
■ Optional integrated surge protection
■ Standard: Q3 surge protection T1+2 up to 1,500 VDC
■ Alternative surge protection manufacturers available on request
PV Fuses
■ Optional integrated PV fuses
■ In positive and/or negative pole possible
QFire BIG PV Firefighter Safety Switch Project Enquiry
Would you like to design the QFire BIG system for a specific project, review technical details or select the right system configuration for your PV installation?
Using the inquiry form below, we collect all relevant project data in a structured and transparent manner.
You can send wiring diagrams, string plans or other technical documents directly with your enquiry. On this basis, we review the technical project requirements, configure the QFire BIG system to suit your project and coordinate the required components. If any queries arise, we will contact you. Otherwise, you will receive a project-specific quotation.
QFire BIG PV Firefighter Safety Switch Project Enquiry
Project-specific enquiry for the design of the QFire system. AI-assisted review, component selection and preparation of a quotation.
Technical Documentation for QFire BIG PV Firefighter Safety Switch
Datasheets, certificates and technical documentation for QFire BIG and QFire LITE firefighter switches, control boxes, switch boxes and accessories.
How QFire BIG Works: Function and Technology
Technical fundamentals of DC-side disconnection, system design, triggering methods, galvanic isolation, and standards-compliant implementation.
FAQ on QFire BIG PV Firefighter Safety Switch
Answers to frequently asked questions about application, standards, triggering concepts, mandatory requirements, and operation of firefighter switches in PV systems.
Fachbeiträge & Pressemeldungen zum Feuerwehrschalter für Photovoltaik
Der Einsatz von Feuerwehrschaltern in Photovoltaik-Anlagen wird in der Branche intensiv diskutiert – insbesondere im Hinblick auf Sicherheit, Normung und Einsatz im Brandfall. Hier finden Sie ausgewählte Fachberichte, Branchenmeldungen und technische Einordnungen.
