POE Network Switches

Things to look for in a POE switch

Output Voltage and Power

Active or Passive?

• A Passive POE switch outputs voltage on the nominated pins at all times.
• An Active POE switch usually operates under one of these standards. An Active POE switch will not apply POE power without first checking to see if the connected device signals back that it can support the POE voltage.

A passive POE device can only be powered by a passive POE switch. Whereas an active POE device (e.g. 802.3af or 802.3at) can be powered by either a Passive or Active POE switch.

Uplink Port(s)

Often you will need to not only power a number of POE devices from the switch, but also to link that switch back into the local network.

• Some switches have normal RJ-45 uplink ports.
• Some have SFP ports for use with fibre modules.
• But what if the POE switch only has powered POE ports? This is actually not often a problem as connecting a POE switch port to a normal RJ-45 LAN port on a non-POE device (e.g. another switch) will usually cause no damage. The reason is that a normal LAN port terminates in such a way that no DC current can flow.