Power over Ethernet (PoE) is a power supply procedure for network components in compliance with IEEE 802.3af and 802.3at. With PoE, power and data are transferred together via the Ethernet cables used which connect the network components. This eliminates the need for addition power lines and thus saves investment and maintenance costs. PoE can be used with all network components that consume little power (max. 12.95 Watt).
In compliance with standard IEEE 802.af, with 10Base-T and 100Base-TX two wire pairs of the Ethernet cable are used for power supply.
In compliance with standard IEEE 802.at, with 100Base-T all four wire pairs of the Ethernet cable are used for power supply.
There are two ways of supplying power with PoE:
- Method 1: Redundant wires
With Fast Ethernet, the wire pairs 1, 2 and 3, 6 are for data transfer. In this case, wire pairs 4, 5 and 7, 8 are used for power supply. If there are only 4 wires in the Ethernet cable, the power supply is modulated onto wires 1, 2 and 3, 6 (see "phantom power supply").
This method supplies the power via two wire pairs of the Ethernet cable in compliance with IEEE 802.3af.
- Method 2: Phantom power supply
In the case of phantom power supply the power is supplied via the wire pairs via which the data is also transferred, i.e. the power is modulated onto the data cable. In the case of Gigabits, all eight wires of the Ethernet cable are used for data transfer and power supply in compliance with IEEE 802.3at. In the case of 10/100 Mbit/s, four wires of the Ethernet cable are used for data transfer and power supply in compliance with IEEE 802.3af.
In the case of PoE, there is a power generator (Power Source Equipment, PSE) and power consumers (Power Devices, PD).
A power consumer (PD) must support both Method 1 and phantom power supply via redundant wires.
A power generator (PSE) can supply power to power consumers (PD) via
- Redundant wires or
- Phantom power supply or
- Redundant wires and phantom power supply.
Power consumers (PD) are the following, for example:
- SCALANCE W-700 Access Points and Client Modules as well as IP cameras, e.g. CFMC1513 and CCMS1315
They support power supply from Power-over-Ethernet (PoE), i.e. they are power consumers (PD) as PoE-compatible terminals. The SCALANCE W-700 Access Points and Client Modules are authorized as PD in compliance with IEEE 802.3af. The SCALANCE W Access Points can be supplied by PSE in compliance with IEEE 802.3at, because the standard IEEE 802.3at is downwards compatible to IEEE 802.3af.
Power generators (PSE) are, for example:
- SCALANCE X Industrial Ethernet Switches X108 PoE, XR324-4M PoE and X308-2M PoE
They permit supply of terminals via Ethernet cables via Power-over-Ethernet (PoE) in compliance with IEEE 802.3at, i.e. they generate the power as power generators.
The SIMATIC NET SCALANCE W700 configuration manual, section 5.2 gives an overview of the SCALANCE W components that support the "Power over Ethernet" function after the hardware redesign. The configuration manual is available in Entry ID: 42784493.