Desktop, Plugtop

Power over Ethernet: Desktop and Plugtop

Power over Ethernet is the designation used for power transfer via a standard Cat. 5/6 twisted pair cable, and not only al ows for the saving of the additional mains power line but also, thanks to the safe low voltage, can be laid by a non-professional. PoE works with voltages of less than 60 V and is therefore classified as SELV (Safety Extra Low Voltage). A distinction is drawn between injectors (PSE – Power Sourcing Equipment), which in turn can be designed as Midspan or Endspan, and consumers (PD-Powered Device).

In principle, there are three power classes according to IEEE:

• IEEE802.3af (15.4 W per port)
• IEEE802.3at (30 W per port)

• IEEE802.3bt (up to 90W per port)

There are also special classes: Ultra/Mega - PoE with 60 and 95W per port respectively.

Desktop and Plugtop versions are straightforward injectors, which in most cases are configured with IEC320-C14 (cold device plugs) or, in rare cases, also as plug-in power units. Likewise, Midspans, i.e. hubs, are often designed as tabletop units, in order to impose power on an existing Ethernet switch. In this case there are 4, 8, 16 and more channels to choose from, with power values of up to 90W per port.