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QFire LITE PV Firefighter Switch for 2 or 4 PV Strings

Compact DC string isolation for 2 or 4 PV strings – galvanic isolation in accordance with IEC 60947-3, up to 1,500 V DC and automatic reconnection when the AC supply is restored.

Functional Principle & Shutdown Logic →

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Difference between QFire LITE vs. QFire BIG →

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QFire LITE PV Firefighter Switch for 2 or 4 PV Strings

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QFire LITE PV Firefighter Switch: Compact Remote DC Isolation for Standardised PV Applications

QFire LITE is a compact PV firefighter safety switch for standardised applications with 2 or 4 PV strings. It is installed close to the PV array or at the point where the DC cables enter the building and galvanically isolates the positive and negative conductors of every connected string when activated.

QFire LITE PV Firefighter Switch is particularly suitable for rooftop systems, façade PV and repeatable system designs with 2 or 4 PV strings per isolation point. It is designed for system voltages up to 1,500 V DC and short-circuit currents up to 20 A Isc per string.

Unlike firefighter switches that use a mechanically latched switch-disconnector, QFire LITE automatically reconnects the PV strings when the AC supply is restored. Manual access to the device is therefore not required following routine mains interruptions.

Four clearly defined variants are available: QFire LITE for 2 or 4 PV strings, each optionally available with integrated Type 1+2 DC surge protection.

QFire LITE 2 PV firefighter switch for two PV strings without surge protection

QFire LITE 4 PV firefighter switch for four PV strings without surge protection

QFire LITE at a Glance

Application	Standardised DC string isolation for applications with 2 or 4 PV strings per isolation point
Function	PV array isolation at the point of installation
Disconnection	Galvanic isolation according to IEC 60947-3
Configuration	2 PV strings or 4 PV strings
MPP Trackers	1 MPPT with LITE 2, 2 MPPTs with LITE 4
System voltage	Up to 1,500 V DC
String current	Up to 20 A Isc per string
Connections	Stäubli MC4-Evo 2, 4–6 mm²
Device Supply	230 V AC
Automatic Reconnection	Yes, when the AC supply is restored
Degree of protection	IP67
Options	Integrated Type 1+2 SPD, external emergency-off switch, key switch and volt-free status contact
Installation location	Sheltered outdoor location
Manufacture	Made in Germany

Operating Principle and Shutdown Logic

How the QFire LITE PV Firefighter Switch Works

QFire LITE is installed in the individual DC string circuits between the PV array and the inverter. During normal system operation, the connected PV strings remain connected to the inverter.

When the 230 V AC supply to QFire LITE is interrupted, the internal switching elements de-energise. The positive and negative conductors of every connected PV string are isolated. The DC cables between QFire LITE and the inverter are then isolated from the PV array and remain de-energised for the duration of the shutdown state.

The Isolation Can Be Triggered By:

interruption of the 230 V AC supply,
an external firefighter emergency-off switch,
a key switch.

QFire LITE PV Firefighter Switch provides galvanic string isolation in accordance with IEC 60947-3. The QFire switching units have been tested at 1,500 V DC and up to 20 A Isc per string.

Operating Principle + Shutdown Logic

The QFire LITE PV Firefighter Switch provides double-pole, galvanic isolation of the positive and negative conductors of the connected PV strings when activated. Isolation can be triggered by:

Interruption of the 230 V AC supply

A defined external control signal

A firefighter emergency-off switch or key switch

External Emergency Stop Switch QFire Firefighter Switch

External Emergency Stop Switch QFire Firefighter Switch Key Switch

When the AC supply is restored, QFire LITE PV Firefighter Switch automatically reconnects the PV strings, provided that no external shutdown condition remains active.

Operating diagram of the QFire LITE PV firefighter switch showing galvanic DC string isolation, 230 V AC shutdown control, emergency-off switch and automatic reconnection

QFire LITE Variants for 2 or 4 PV Strings

QFire LITE is available in four clearly defined standard variants. Applications with 2 or 4 PV strings can therefore be selected, designed and installed quickly and efficiently.

QFire LITE Firefighter Switch 2 Strings 1 Surge Protection

Variant	PV Strings	MPP Trackers	Surge protection	Enclosure
QFire LITE 2	2	1	None	300 × 300 × 132 mm
QFire LITE 2 + SPD	2	1	Type 1+2, 1,500 V DC	300 × 400 × 132 mm
QFire LITE 4	4	2	None	300 × 300 × 132 mm
QFire LITE 4 + SPD	4	2	Type 1+2, 1,500 V DC	300 × 400 × 132 mm

Automatic Reconnection

Automatic Return to Operation After Mains Restoration

If the AC supply fails, QFire LITE automatically enters a safe state and isolates the connected PV strings.

As soon as the AC supply is restored and no external shutdown condition remains active, QFire LITE automatically reconnects the PV strings. No manual reset at the device is required following a routine mains interruption.

This is particularly beneficial for:

difficult-to-access roof areas,
facade PV and high-rise buildings,
systems with multiple distributed isolation boxes,
installations subject to frequent short mains interruptions,
commercial PV systems where unnecessary downtime must be avoided.

Automatically Isolate Safely – Automatically Resume Generation

QFire LITE combines galvanic DC string isolation with automatic reconnection when the AC supply is restored. The PV system therefore remains safely isolated during a mains failure without requiring an engineer to access the roof after every supply interruption.

Difference from Conventional Firefighter Switches with an Undervoltage Release

With conventional DC switch-disconnectors using an undervoltage release, loss of the AC supply mechanically trips the switch to the OFF position. After the mains supply has been restored, these designs remain in position 0 and must be reset locally.

QFire LITE PV Firefighter Switch uses voltage-dependent, fail-safe isolation logic. If the control voltage is lost, the PV strings are isolated. When the supply returns and the shutdown circuit has been released, the system automatically reconnects the strings.

This eliminates the need for manual access to the isolation device following routine mains interruptions.

QFire LITE PV Firefighter Switch Technical Data

Technisches Merkmal	Design
Switching Method	Galvanic isolation
Disconnection	Positive and negative conductors of each PV string
Number of strings	2 or 4
MPP Trackers	1 with LITE 2, 2 with LITE 4
System voltage	Max. 1,500 V DC
String current	Max. 20 A Isc per string
Device Supply	230 V AC
Site-Provided Protection	B6 miniature circuit breaker
DC Connection	Stäubli MC4-Evo 2
Conductor Cross-Section	4–6 mm²
Enclosure Material	Polycarbonate
Degree of protection	IP67
Impact Resistance	IK08
Operating Temperature	−25 °C to +50 °C
Installation location	Sheltered outdoor location
Automatic reconnection	Yes
Options	Type 1+2 SPD, external emergency-off switch, key switch and volt-free status contact

QFire has been tested in accordance with IEC 60947-3 at 1,500 V DC and 20 A per string.

The corresponding German adopted standard is DIN EN IEC 60947-3.

Learn More About QFire Technology →

QFire Feuerwehrschalter Photovoltaik Variante LITE standardisierte wirtschaftliche Loesung

Comparing QFire LITE and QFire BIG

Feature	QFire LITE	QFire BIG
System Concept	Standardised applications	Project-specific and custom-engineered applications
PV Strings per Enclosure	2 or 4	Up to 24
System voltage	Up to 1,500 V DC	Up to 1,500 V DC
String current	Up to 20 A Isc	Up to 20 A Isc
Configuration	Defined standard variants	Freely configurable
Surge protection	Optionally integrated	Can be integrated to project requirements
PV Fuses	Not included in the standard variants	Optionally integrated
Connection concept	MC4-Evo 2	MC4-Evo 2, H4, Sunclix or terminal connections
Cluster Control	No	Yes
Shutdown Control Method	Standardised via the 230 V AC supply or an external switching device	Project-specific via control box, emergency-off switch, key switch, fire alarm control panel or AC-side shutdown concept
Typical application	Standardised isolation points with 2 or 4 PV strings, facade PV and repeatable system designs	Commercial and industrial PV, logistics roofs and complex PV array configurations

PV System Safety Architecture

Case Study: QFire LITE for Facade PV

In façade PV and high-rise projects, individual PV strings may enter the building floor by floor or façade section by façade section. QFire LITE provides clearly defined isolation points directly where the DC cables enter the building.

Multiple QFire LITE units can be isolated simultaneously via a centrally switched 230 V AC supply. When activated, each unit locally and galvanically isolates its assigned PV strings. This creates a transparent safety architecture with a clear allocation of strings to specific building sections or floors.

Solution with QFire LITE

A QFire LITE firefighter switch is installed on each floor directly at the entry point of the DC lines. In the event of triggering, galvanic isolation of the PV strings occurs immediately before entry into the building.

The QFire LITE units can be controlled centrally via a looped-through 230 V AC supply. If this supply is interrupted in the event of a fire – e.g., via a central firefighter emergency stop in the basement – all connected firefighter switches shut down simultaneously.

View practical example: QFire LITE for facade PV →

Advantages of this solution

Galvanic DC isolation at the defined building entry point

Central activation with distributed local isolation

A standardised solution for repeatable isolation points

Frequently Asked Questions About the QFire LITE PV Firefighter Switch

What Is the QFire LITE PV Firefighter Switch?

QFire LITE is a compact isolation device for PV systems with 2 or 4 PV strings. When activated, it galvanically isolates the positive and negative conductors of the connected strings between the PV array and the inverter.

What Happens in the Event of a Mains Failure?

If the 230 V AC supply fails, QFire LITE automatically enters the safe state. The PV strings are isolated from the inverter at the installation point of the device.

Does QFire LITE Reconnect Automatically After a Mains Failure?

Yes. As soon as the AC supply has been restored and the external shutdown circuit has been released, QFire LITE automatically reconnects the connected PV strings.

How Many PV Strings Can QFire LITE Switch?

QFire LITE is available for 2 PV strings with one MPP tracker or for 4 PV strings with two MPP trackers.

What Information Is Required for Technical Sizing?

For a fast and reliable design, the string plan, inverter type, number of MPPT, string allocation per MPPT and module data are particularly helpful. In addition, information on short-circuit current (Isc), the desired protection concept and the connection technology is required.

How Does QFire LITE Differ from Eaton SOL30 and SOL30x-Safety?

Eaton SOL30 and SOL30x-Safety use an integrated undervoltage release and a mechanical switch that returns to the 0/OFF position. QFire LITE also isolates the connected PV strings automatically if the AC supply fails, but reconnects them automatically when the supply is restored, provided no external shutdown condition remains active.
QFire LITE is also designed for system voltages up to 1,500 V DC, whereas Eaton specifies up to 1,000 V DC for SOL30 and SOL30x-Safety.

When Is QFire BIG Required Instead of QFire LITE?

QFire BIG is intended for systems with more than four PV strings, custom connection concepts, cluster control, integrated PV string fuses or complex AC- and DC-side shutdown requirements.

QFire LITE Project Enquiry

Would you like to design the QFire LITE system for a specific project, have technical details checked, or select the appropriate system configuration for your photovoltaic system?

Using the inquiry form below, we collect all relevant project data in a structured and transparent manner.

You are welcome to send wiring diagrams, string plans, or other technical documents directly. Based on this, we will check the technical framework, design the QFire LITE system to suit your project, and coordinate the components specifically.
Should any questions arise, we will contact you. Otherwise, you will receive a project-specific offer directly.

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Project Inquiry Firefighter Switch

Project-specific inquiry for QFire system design. Component selection and quotation preparation.

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Firefighter Switch Technical Download

Data sheets, certificates, and technical documentation for QFire BIG and LITE, control boxes, switch boxes, and accessories.

Technical Documentation for Firefighter Switch →

Wann ist bei einer PV Anlage ein Feuerwehrschalter Pflicht?

Functionality & Technology QFire

Technical fundamentals of DC-side disconnection, system design, triggering methods, galvanic isolation, and standards-compliant implementation.

Functionality + Technology Firefighter Switch →

FAQ on Firefighter Switches

Answers to frequently asked questions about application, standards, triggering concepts, mandatory requirements, and operation of firefighter switches in PV systems.

FAQ on Firefighter Switches →

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