In a basic PoE power supply system, the major components are the power sourcing equipment (PSE), the powered device (PD), and the PoE cables. When a problem occurs with PoE, in most cases, the error symptom can be simply shown as the powered devices will power off and stop working while the cause of failure may be many factors, including the hardware device factors and software factors. How to precisely recognize the root of the PoE errors and minimize troubleshooting time? This post will elaborate on the three common PoE error symptoms and the troubleshooting methods.
A PoE PD failing to boot up is one of the most frequently seen errors among PoE errors. It may be caused by the PoE component issues or the wrong configuration command. Follow the steps listed below to solve the problems:
If you are certain there are no quality issues over your PoE network switch and PD and they all support PoE functions, you will need to confirm whether PSE and PD both conform to PoE IEEE standards. Note that non-standard PoE switches, also called passive PoE switches, always deliver power over the Ethernet lines at a certain voltage regardless of whether the terminal device supports PoE or not. If not well prepared, it may burn out the terminal devices.
Also, the power modes of PSE and PD are other factors that may cause PoE problems. There are three PoE modes: Alternative A, alternative B, and 4-pair delivery. Remember to confirm the power supply modes of PSE and PD with the vendor. If a PD only supports PoE mode B power delivery, while a PoE switch is based on Alternative A, as a result, the PD and PoE switch can not work together.
Mismatching the Ethernet cable for PoE and the port can lead to network failure. Thus it is suggested to affirm the available Ethernet port for PoE before powering the PD on. Of course, if the cable has hardware failure or it is not a qualified one, there will be PoE errors as well.
Theoretically, the PSE device interface can detect the PD automatically when the PD is connected. If the power is insufficient to provide the required power for PD, the PD will not get powered. Make sure the power for running the PDs will not exceed the power budget of the PoE network switch. If a PSE has detected the PD’s power class is within its capacity, it will power the PD on.
Check whether automatic PoE power management configuration is configured on the switch interface. If not, you will need to manually deliver PoE power to the PDs connected to the PoE network switch interfaces.
What if a working PD stops powering on or reloads internittenly？The phenomenon of keeping reloading or getting powered off in the midway of running can be the result of insufficient power supply and poor quality PoE cables.
A PoE PD may get powered off or reloads intermittently when the PSE output power is not sufficient for all the PDs running at full power consumption. Take IP CCTV cameras as an example. It is likely for the PD to draw a lot more power than required for its normal operation during the process when they run through a test of all their extended functions such as Pan-Tilt-Zoom, heaters, wipers, etc. If there is no available extra power, the camera may get stuck in a continuous boot cycle. To troubleshoot this PoE error, one should measure how much power the CCTV camera requires during startup and use the right PSE to offer sufficient power.
If the Ethernet cable used in a PoE link is over 100 meters or has power loss due to material and resistance of the cable itself, the PD would not get sufficient power, causing issues like network failure or stuck. If the cables are not qualified, it will lead to errors as well.
If there are certain numbers of PDs available to get powered while others are still powered off, you should check as the following tips suggest:
Check whether it’s the fault of certain ports on the PSE. Disconnect the PoE cable between the Ethernet switch port and the PDs which are unavailable to get powered. If the PDs can receive power when connected to other PoE ports, it proves the fault on certain ports. Use the configuration command to verify if the port is shut down or error-disabled. If so, run the command to enable PoE functions.
If the PDs are newly added on PSE ports and the PoE switch power budget is depleted, they will not power on. Make sure the remaining PoE power of PSE is not smaller than the maximum output of the port to which PDs are connected. Limit the per-port current at safe levels and use the extra PSE devices if needed.