When is a firefighter switch mandatory for a PV system?
Legal requirements, standards, and practical examples for planners, installers, and operators
The safety of photovoltaic systems (PV systems) is a key issue, especially in the event of a fire. Technical standards and regulations play a decisive role here. DIN VDE 0105-100 governs the general requirements for operating electrical installations, while the application rule VDE-AR-E 2100-712 defines specific requirements for shutting down PV systems for emergency services. In addition, IEC 60947-3 specifies the requirements for switching devices and disconnectors that ensure safe shutdown. These standards form the technical basis for deciding when a firefighter switch is mandatory.
At a time of increasing use of renewable energy, photovoltaic systems are an important part of the energy transition. However, alongside their enormous potential for CO2 reduction, safety aspects are also in focus. PV system planners are repeatedly confronted with the question of whether it is necessary to use a firefighter switch. But what is the legal situation here? When is a firefighter switch mandatory? Which standard requires such a switch, and what arguments can be used to justify the additional costs to the customer?
Technical basis
In electrical installations, the ability to isolate devices and cable runs is an essential part of the safety requirements. To illustrate this in a simplified way, let us look at the following diagram.
Shown are a generator and a connected load. Where would a professional ideally install the isolation point here?
If the isolating device were placed near the load, operating the switch would de-energize only the short section between the switch and the load—but the long cable run between the generator and the switch would remain energized. This entails risks, especially during maintenance work or in an emergency.
The optimal position for the isolator is therefore as close to the generator as possible. This ensures that as much of the cable between the generator and the load as possible can be de-energized.
This fundamental safety requirement is described in DIN VDE 0105-100. This standard defines the five safety rules for working on electrical installations, including the need to isolate live parts. That the cable between the generator and the load is included goes without saying and is an indispensable principle.
The particular challenge with PV systems
If we now consider this for a PV system, the generator corresponds to the photovoltaic system (PV modules). This means that the entire cable between the PV modules and the load—typically the inverter or the electrical distribution—must be de-energized in order to meet the safety requirements in accordance with DIN VDE 0105-100.
DIN VDE 0100-712
There are dedicated standards for PV systems that govern isolation, particularly on the direct current (DC) side. A key role is played by DIN VDE 0100-712, which defines requirements for the electrical safety and installation of PV systems. It requires that an isolation option be provided on the DC side of the PV system, in particular for maintenance work or hazard prevention.
A particular challenge is the DC voltage itself. Unlike AC, direct current has no zero crossing and, when simply switched off, will very quickly generate an arc, which poses particular hazards. This can lead to fire; the switch can “weld” and fail to interrupt the current flow; components can burn out. Switching DC in PV systems is therefore governed by IEC 60947-3.
Most inverters have an integrated DC isolator that complies with IEC 60947-3. However, if the inverter is not installed directly next to the modules, it is in the wrong place. If, for example, the inverter is installed in the basement and the cables run through the entire building, these cables—some carrying voltages of up to 1,500 volts—cannot be isolated in the event of a fire or even for maintenance! This poses a danger to life and limb in such situations and must definitely be avoided!
In order to be able to isolate the cable between the PV modules and the inverter as well, the isolator must be placed close to the generator, as described in the example above.
What does VDE-AR-E 2100-712 say?
The application rule clearly describes how the risk of electric shock, e.g. in the event of a fire, can be minimized—or better, eliminated—by using firefighter switches. Based on the standards described above and a clear technical understanding of the application and the potential hazards, it shows that PV systems must provide a means of protection close to the modules. Switching is carried out by galvanic isolation or short-circuiting in order to comply with this application rule. It should be noted that shutdown itself must be possible either via an external, accessible switch and, in an emergency, also by disconnecting the mains voltage. It should also be noted that, in the event of a power failure, switches should be able to automatically switch the system back on when power returns and no emergency is present.
Ultimately, the application rule is only a general nationwide recommendation in Germany to install such a switch, but it becomes mandatory regionally or through tender specifications!
Conclusion
When is a firefighter switch mandatory? The combination of applicable standards, application rules, the state of the art, and ultimately the responsibility of the qualified electrician and system planner to build a system as safely as possible makes the use of a firefighter switch almost unavoidable in many constellations. While for small systems—for example in the area of private single-family homes—a simple DC isolator or a manually switchable PV fuse will probably suffice, large rooftop systems for public buildings with a fire alarm control panel require more complex systems with an external key switch and, if necessary, online monitoring. For large systems, firefighter switches can usually be combined quite well with the surge protection that is required anyway, which can help minimize costs. Making long DC cables that carry up to 1,500 volts “non-disconnectable” is negligent, and as a professional you should not get involved in anything like that!
About the author
Thomas Neumann, Managing Director of Q3 ENERGIE GmbH & Co. KG, is a recognized expert in shutdown technologies in the photovoltaic sector. Since 2011, Q3 has been developing and marketing innovative solutions that increase the safety of PV systems. With more than a decade of experience, the company is one of the pioneers in the industry and sets standards for the safe operation of photovoltaic systems.