The power over Ethernet inject the power to cat5e or cat6 network cable, so the remote ip devices is able to retrieve both power and data from single cable at the other end. According to the standard EN62368 (for AV & IT Equipment), the limit at which under no safeguards are required is DC60V or 2mA. We are seeing different voltage not higher than or equal to DC57V are being used on power over Ethernet. Let’s talk about the differences about these voltage on power over Ethernet.
One thing need to be addressed before we move ahead is the voltage drop. While using cable to send the power, there is always power loss inline cable which will be converted to the heat. The consequently result is the voltage drop at the other end. If the voltage drop down lower than the remote devices require, the whole system will stop working. For example, the WiFi router requires DC9V, but the remain voltage is only 7V after 100 meters transporting, the power will not be able to supply the WiFi router.
DC12 voltage power
This is the raw solution. The power is injected to the spare pairs of the Ethernet cable and being sent to the remote network devices. There is no process and protection for the power. This is the most simplest PoE solution which could still work for short distance and low power consumption on indoor application. If use this solution to transport power longer than 20 meters, the remain voltage will drop down sharply at the other end.
DC24 voltage power
It is popular in some telecom application. Some of electrical devices require DC12V input. Injecting DC24V to the cable can adapt to the voltage drop after medium distance transportation such as 50 meters. The other side usually requires voltage regulator to convert remain voltage to DC12V. There is around 12V margin to adapt to the voltage drop, that is why the maximum distance could be longer.
DC48 volts power
DC48V is the specification from IEEE802.3 PoE standard. According to IEEE802.3, the power is capable of transporting up to 100meters as well as data. The other end requires regulator to convert to lower DC output such as 12V or 5V. IEEE802.3 also specified the power budget within 100meters including PoE PoE+, PoE bt. The higher power consumption, the higher the current inline, so the sharper voltage drop will be. As long as the products are IEEE 802.3 compatible, the voltage is no need to be concerned. Both issues has been considered when the standard was developed. Not only IEEE802.3 standard PoE use DC48V. Some of the passive PoE also use DC48V.
Over DC48 voltage
In these years the higher voltage such as DC55 has been applied to power over Ethernet including IEEE 802.3 compatible products. The benefits of high voltage PoE is reducing the power loss cable inline and relase the voltage drop issue. For example the IEEE 802.3bt PoE power system can transport 95w power over single Ethernet. If use DC48V, the voltage drap becomes seriously when the power is being full load. The DC53V is taken in, so the remain voltage is still enough after 100 meters transporting.
IEEE 802.3 PoE is considered as safe power system. That is because not only the power voltage has been designed for Ethernet cable, but also PD signature is introduced in the standard to guarantee the power PD signature is being sent to the device.
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