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Make Clear PoE and Non-PoE? This Post is Enough

The concept of simultaneous supply of power and data through the same cable is nothing new in telecommunications (the POT system carries voice signals while the instrument remains on through the power supply), but Power over Ethernet (PoE) has stepped up a notch, taking this simple concept to a higher level. With the expansion of IoT devices, PoE has become the ideal solution in large-scale network systems that call for a reliable power/data connection. But there are still many questions when it comes to the actual application of PoE technology “What happens if a non-PoE device is connected to a PoE Ethernet port? Is there any hazard of mixing PoE and non-PoE devices in the same network?” In this post, we’re gonna figure out what is PoE and non-PoE and how to mix them together in the same network.

PoE and Non-PoE?

At its simplest, PoE transfers low-voltage electrical currents along with data to the powered devices (PDs) at high frequency via a single Ethernet cable at a maximum distance of 100M. Technically, PoE features a point-to-point connection from power sourcing equipment (PSE) to PDs. The PSE delivers the power over the Ethernet, while the PD extracts the power from the Ethernet. Depending on whether the device is compliant with the IEEE 802.3 standards, it can be further classified into active/standard PoE and passive/non-standard PoE. The former will testify the connection before releasing power, while the latter has no such feature. On the other hand, non-PoE only provides data between two devices and a separate power source is required to power up incompatible devices. PoE oftentimes delivers its power at 48V and compatible PDs will simultaneously convert this voltage to an acceptable level, while non-PoE devices have no such protective mechanism for DC power conversion and they will get severely damaged if the wrong voltage is connected.

Mixing PoE and Non-PoE Devices——Any Problems?

Ethernet has been in existence for decades, while PoE is a rather novel concept. Inevitably, most network devices available in the market are non-PoE compatible (i.e routers, laptops, and Raspberry Pi). Therefore, the first and foremost priority is to ensure the safety of mixing PoE and non-PoE devices in the same network. When connected to a non-PoE device, the PoE injector will first initiate a “negotiation” procedure to guarantee a valid PoE-compatible device is plugged in. If the feedback is negative, the PoE switch will only supply power to the incompatible device to prevent potential hazards. And when adding a PoE injector or splitter to the existing network infrastructure (without PoE), the negotiation will be carried out by the PoE-compatible devices to ensure the safe operation of non-PoE devices.

It is worthwhile to mention that this negotiation process is only available in active PoE that is compliant with IEEE 802.3 standards. Nevertheless, in passive PoE, which is only capable of supplying power to the connected devices at a certain voltage, no power negotiation will take place. What’s more, it should be noted that if connected to an incompatible device, a passive PoE injector compliant with IEEE 802.3af standard specifies a total power output of 15.4W at 48V would cause irreversible electrical damage to the PD. Accordingly, as long as you deploy an active PoE device that performs a “handshake or negotiation” for power verification, there won’t be any problems mixing PoE and non-PoE devices on the same network.

What is PoE Handshake/Negotiation?

This PoE handshake or negotiation procedure is essentially crucial to ascertain that a testified PoE equipment (switch or injector) is connected in the network to ensure the safe and reliable operation of incompatible devices. The negotiation process is normally comprised of three stages: detection, classification and operation.

Detection: During this step, the PSE will send a detection signal to the connected devices to ensure it only powers valid PoE-compatible PDs. It will periodically check if a compatible device is plugged in or if the PD is within a correct signature resistance range between 15–33 kΩ by sending a low-voltage pulse at 2V-10V (harmless even to non-PoE devices) down the cable until the connection is confirmed. Failure to confirm the compatibility between PSE and PD may have catastrophic impacts on the network, including power outages, network crashes to imminent fire hazards.

Classification: After the detection, the PSE inquires how much power the PD is requesting so that it can allocate the appropriate amount of power to that load. In the classification, the PSE will categorize the PDs into different classes depending on their power requirements on the rankings of 0-8. Each PD will only draw as much power as the PSE promises to prevent the conditions of over-voltage. PoE classes play a pivotal role in ensuring efficient power distribution by measuring the amount of power a PD requires and thereby allowing PSE to reallocate surplus power to high-power devices, such as LED lighting and POS system.

Operation: After measuring the amount of power each terminal device needs, the active PoE devices (PoE switch or injector) will start to provide a low voltage to the PDs (typically less than 15 microseconds) at first and then gradually increase to the full 48V DC power. During this procedure, the PoE switch or PoE injector will convert the AC power to DC power to reduce the considerable interference caused by alternating currents. If the valid PoE device is disconnected from the network midway, PSE will immediately withdraw the DC power to safeguard the PoE port and in case a non-PoE device is mistakenly connected. What’s more, if an over-current condition occurs, the PSE will simultaneously go into the protection mode, cut off the power supply (within 0.3-0.4 seconds) and restart the detection and classification cycle when enabled so as not to damage the connected devices.

Ways to Mixing PoE and Non-PoE Devices

#1 Connect Non-PoE switches with PoE Devices-PoE Injector

The PoE injector plays a supplementary role in the entire PoE system to enable the non-PoE devices like regular network switches to work with the PoE-compatible devices. The injector adds PoE capability to the regular Ethernet switch and enables it to power PoE-compatible devices in hard-to-reach areas when only a few PoE ports are required with a minimal impact on the existing network system. It offers a versatile solution to power valid PoE devices by converting the AC power into DC power, integrating the power and data into one source and transmitting it to the PD. The PoE injector creates connections to high-power applications at high frequency, such as 90W LED lighting, PTZ cameras and high-performance wireless access points, with improved network speed and less latency. It usually works together with PoE or non-PoE switches for networking and data uploading.

A PoE injector normally has three ports: a power input port, a data input port and a PoE/ data and power output port. First, take a Cat5 Ethernet cable, plug one end into one of the RJ45 ports in the network switch and plug the other end into the data input port on the injector to set up the data connection. An additional power source is needed to power the injector and the PD, you’ll need to take a power cord/adapter, connect it to the PoE injector and plug it into an electrical outlet. Then use a second Ethernet cable to connect the injector and the PD.

#2 Connect PoE switches with Non-PoE Devices-PoE Splitter

PoE splitter is a revolutionary device that works with a PoE injector or PoE switch to power non-PoE devices by splitting the power from the data and feeding it to a separate input that a non-PoE compliant device can use after receiving the power and data transmitted from the injector/ PoE switch. Installing a new outlet near the edge device is quite expensive, but the PoE splitter offers a cost-effective method to power non-PoE devices with PoE power supply equipment without large-scale changes of the network facilities, which helps you save a large sum of money on installation. And thanks to the PoE handshake, the PoE splitter can provide an appropriate amount of power to the non-PoE devices without burning down them.

Normally, a PoE splitter has a PoE input port at the one side and two short output cables (one for power output; another for data output) on the other side, but the 95W industrial-grade PoE splitter from Fastcabling is greatly advanced, transforming the output cables into power and data (LAN) output ports for future expansion in long-distance deployments. First, connect the PoE injector/switch with an Ethernet cable (plug it into the PoE input port); then use another two cables to connect the splitter and the non-PoE device. Additionally, the splitter can work with the injector to set up a PoE power link between non-PoE network switches and PDs.

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