PoE delivers DC electrical power over Ethernet cables to connected network devices. Once connected and enabled, passive PoE injects a predetermined level of DC current onto the Ethernet cable, powering any connected PD on the circuit.
Passive PoE is most often employed in PSEs such as injectors, and sometimes midspans, but rarely in PoE switches.
Unlike standards-based PoE, passive PoE will not negotiate with the PD to determine the parameters of the levels of current to be sent. The parameters are hard-wired within the PSE.
This makes passive PoE more suitable for specialized applications where higher power, or longer than standard cable runs are required. However, it should be used carefully, as a mismatched PSE and PD could cause permanent damage to either the PD, the PSE, or both.