Challenge: When is a fireman’s switch mandatory for a PV system?

The safety of photovoltaic systems (PV systems) is a key issue, especially in the event of fire. Technical standards and regulations play a decisive role here. DIN VDE 0105-100 regulates the general requirements for the operation of electrical systems, while the VDE-AR-E 2100-712 application rule defines specific requirements for the shutdown of PV systems for emergency services. In addition, IEC 60947-3 specifies the requirements for switchgear and disconnectors that ensure safe disconnection. These standards form the technical basis for deciding when a fire department switch is mandatory.

In times of increasing use of renewable energies, photovoltaic systems are an important part of the energy transition. However, in addition to their enormous potential for reducing CO2, the focus is also on safety aspects. Planners of PV systems are repeatedly confronted with the question of whether it is necessary to use a fire department switch. But what is the legal situation here? When is a fireman's switch mandatory? Which standard prescribes such a switch and what arguments can be used to justify the additional costs to customers?

In electrical installations, the ability to disconnect devices and cable routes is an essential part of the safety requirements. To illustrate this in a simplified way, let's look at the following drawing.

A generator and a connected load are shown. Where would the specialist ideally install the disconnection option here?

If the disconnection device were placed close to the load, only the short distance between the switch and the load would be de-energized when the switch is actuated - the long cable path between the generator and the switch, however, would remain energized. This poses risks, especially during maintenance work or in an emergency.

The optimum position for the disconnector is therefore as close as possible to the generator. This ensures that the entire line between the generator and load can be de-energized as far as possible.

This basic safety requirement is described in DIN VDE 0105-100. This standard regulates the five safety rules for working on electrical systems, including the need to disconnect live parts. It goes without saying that this includes the line between the generator and the consumer and is an indispensable principle.

If we now look at a PV system, the generator corresponds to the photovoltaic system (PV modules). This means that the entire line between the PV modules and the load - typically the inverter or the electrical distribution system - must be de-energized in order to meet the safety requirements in accordance with DIN VDE 0105-100.

PV systems have their own standards that regulate disconnection, particularly on the direct current (DC) side. DIN VDE 0100-712, which defines the requirements for the electrical safety and installation of PV systems, plays a central role here. It requires that a disconnection option must be available on the DC side of the PV system, in particular for maintenance work or to avert danger.

The DC voltage itself poses a particular challenge. In contrast to alternating current, direct current has no zero crossing and will very quickly generate an arc if simply switched off, which poses particular dangers. Fire can occur, the switch "sticks" and does not interrupt the current flow, components burn. The switching of direct current in PV systems is therefore regulated in IEC 60947-3.

Most inverters have an integrated DC disconnector that complies with IEC 60947-3. However, if the inverter is not installed directly next to the modules, this is in the wrong place. If the inverter is installed in the basement, for example, and the cables run through the entire building, these can sometimes carry voltages of up to 1,500 volts and cannot be disconnected in the event of a fire or for maintenance! This poses a danger to life and limb in such situations and should definitely be avoided!

In order to be able to disconnect the line between the PV modules and the inverter, the isolating switch must be placed close to the generator as described in the example above:

And this is precisely the structure described in VDE-AR-E 2100-712.

The application rule clearly describes how the risk of electric shock, e.g. in the event of a fire, can be minimized or even better eliminated by using fire department switches. Based on the standards described above and the clear technical understanding of the application and possible hazards, it is shown that PV systems must have a fuse option close to the modules. Switching is carried out by galvanic isolation or short circuit in order to fulfill this application rule. It should be noted that the disconnection itself must either be carried out via an external, accessible switch and, in an emergency, must also be possible by switching off the mains voltage. It should be noted that in the event of a power failure, switches should also be able to switch the system back on independently when the power returns and there is no emergency.

The application rule is ultimately only a general recommendation throughout Germany to install such a switch, but is mandatory regionally or by tender!

When is a fireman's switch mandatory? The combination of applicable standards, application rules, the state of the art and ultimately also the responsibility of the electrician and the system planner to install a system as safely as possible make the use of a fireman's switch almost unavoidable in many constellations. While a simple DC disconnector or a manually switchable PV fuse is probably sufficient for small systems, for example in private single-family homes, more complex systems with external key switches and possibly also online monitoring are required for large rooftop systems for public areas with a fire alarm control panel. In the case of large systems, the fire department switches can usually be combined quite well with the surge protection that is required anyway, which can help to minimize costs. Making long DC cables, which carry up to 1,500 volts, "non-disconnectable" is negligent and professionals should not get involved here!

Thomas Neumann, Managing Director of Q3 ENERGIE GmbH & Co. KG, is a proven expert in shutdown technologies in the field of photovoltaics. Q3 has been developing and selling innovative solutions that increase the safety of PV systems since 2011. 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.

Feuerwehrschalter von Q3 – Sicherheit seit 2012

Seit 2012 entwickelt und produziert Q3 zuverlässige Feuerwehrschalter für Photovoltaikanlagen – mit dem klaren Ziel, maximale Sicherheit für Einsatzkräfte und Anlagenbetreiber zu gewährleisten. Unsere innovativen Lösungen zur Modul- und Stringabschaltung entsprechen den aktuellen Normen und ermöglichen eine einfache Integration in neue sowie bestehende PV-Anlagen.

Erfahren Sie mehr über unsere Produkte und deren Vorteile:

🔗 Feuerwehrschalter für PV-Anlagen