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Many Internet connected devices, such as IP cameras, VoIP phones, WIFI radios, and Ip access card readers, use Power over Ethernet. A single network cable transmits data and power to the device, making installation simple. Data uses one set of wires, and power uses another set of wires in a network cable.

Devices that plug power into certain wire pairs in an Ethernet cable are called injectors or MIDSPAN. Use a separate power supply (injector) or use an Exchanger containing built-in PoE to inject power to an Ethernet cable. Many devices using PoE comply with the IEEE standard. But be careful. Some devices don't meet this standard. Before using PoE, it is important to know exactly what voltage and current is required for the device. Here's a review of the technology.

 

In all cases, electricity is sent over a network line. In diagram A, power is supplied on the same wire as the signal. In Mode B configuration, power is provided through two sets of optional wires in the network cable.

The following figure shows the pattern a configuration. The power supply is provided by a Exchanger, which Exchanger includes a PoE on a port or an injector connected between the switch and the device.

 

 

The following figure shows the Mode B configuration. In this case, power from the switch or ejector is supplied on a separate network line. Many devices are designed to receive power using either mode a or mode B.

 

 

There are some passive PoE sources and there are “active” or “smart” type sources.  The “active” type communicates with the device. This provides device protection that can prevent damage caused by short circuits, as well as providing overcurrent and overvoltage protection. The passive PoE sources are less expensive and provide power without any verification from the device.

 

Power sources that conform to the IEEE standard include network switches individual or multiport PoE injectors (or midspans).