The present invention is in the field of Power over Ethernet (PoE) systems comprising a power supply module and an operation module with an emergency operation mode for operating lighting means, wherein the power supply module supplies a supply voltage via a data cable to the operation module. Especially, the present invention relates to power supply modules, preferably Power Sourcing Equipments (PSE) according to the PoE standard; operation modules with an emergency operation mode, preferably Powered devices (PD) according to the PoE standard; PoE systems, comprising such power supply modules and operation modules; and a detection method for detecting whether an operation module is arranged for operating lighting means in an emergency operation mode as well as an emergency operation mode triggering method for triggering an operation module to operate lighting means in an emergency operation mode.