Fireman's Switch for PV Systems - Module String Disconnection

The QFire Switch fireman's switch disconnects all lines from the roof junction box from the PV generator when switching. This means that all DC lines in the building are de-energised. Switching takes place via the control box, which is ideally located close to the inverters or connected to another point on the AC grid.

The main advantage of the AC-coupled disconnection system is that in the event of a fire, for example, there is no need to search for or access a switch. When the AC mains is switched off, the DC lines are also automatically disconnected from the roof switch box. When the AC mains supply is restored, the system will automatically restart.

Up to five different roof areas can now be controlled from a single control box. In addition to 'on' and 'off', each individual cluster also signals the status of the line and, if necessary, the functionality of the surge protection.

The distance between the control box and an individual cluster can be up to 300 metres. In the event of a power failure, all clusters will go into a safe state and automatically switch on when the power is restored. In the event of a power failure, all strings of the entire system are disconnected from the PV generator by the control boxes and are thus safely de-energised.

In most cases, the inverter is installed close to the house's power distribution system in a central location in the building. This can be switched off, as can the entire electricity in the house. What cannot be switched off is the voltage coming from the modules: Here, up to 1,000 volts direct current remain in the building. Note: from 120 V direct current, this is considered life-threatening.

This not only concerns the fire brigade in case of fire, according to which a minimum distance of up to 5 metres (depending on whether a spray or extinguishing jet is used) must be kept from live parts, but also maintenance and cleaning work, etc. Self-protection takes precedence over external protection.

Therefore, the unanimous wish is for a safe shutdown device for photovoltaic modules in order to be able to completely disconnect the building from the power supply in the event of a fire, i.e. also from the DC side.

QFire is a PV generator disconnection device for automated galvanic isolation of PV strings according to DIN EN 60947-3:2020.

The set consists of a control box and one or more switchboxes.

The QFire control box is installed centrally near the inverter or at another accessible location. The QFire switch boxes are installed near the module at the roof inlet, from where all lines coming from the roof can be switched off safely and without arcing using special high-performance relays. In this way, the entire direct current supply can be interrupted from a central point.

With the QFire fireman's switch, the power is switched off

manually at the control box
via an external EMERGENCY OFF or key switch
coupled via the fire alarm panel
AC coupled via the mains supply in the event of a mains failure
if the mains supply switches back on, the system automatically goes into operation again
by undervoltage due to cable breakage or in the event of strong fluctuations in the AC mains supply