It is not unusual that the lines between the PV modules and the inverter can be long and are placed in cable routes together with AC cables. PV modules cannot be turned off by other means than shut out the light, hence the DC cables through the building are live. Live cables increase the hazard for the firefighters during a fire.
The fireman’s switch is a DC disconnect switch equipped with a time delay undervoltage release. The time delay ensure that more than 93% of all brief power failures and voltage drops will not cause a trip. All fireman’s switches feature NO-NC auxiliary contacts to be used for switch position indication.
Swedish Fire Departments have started to recommend increased safety measures, allowing safe operation for the firemen in buildings with PV systems.