I have to measure the power consumption behavior of switches which are powered with PoE and which also provide energy to other devices. How can this be done?



If I am reading your question right, you have an edge switch that is both POE-PD (powered device) and is also a POE-PSE (power sourcing equipment). I assume this switch is hooked up to a larger distribution switch which is capable of generating enough power per port to supply the combination of the edge switch and some combination of endpoints like IP phones or cameras.

If your distribution switch is a Cisco, then show power inline {port} will show POE power used by that port. So first plug in the switch by itself and measure power draw at the distribution switch port. Then plug in each device and measure the incremental power draw.

Also if you are feeling motivated, you could plug your endpoints into the distribution switch directly and measure their power draw individually. This would give you some insight into any additional power loss due to the cascaded POE setup.


If the switch is managed it is a very good possibility to have snmp enabled. If that's the case you will have to setup a client that pulls at regular intervals the values from the snmp OID in respect to power consumption.


you cannot if the POE switch does not have it's own management interface. there are many passive POE switch and device which consumes power only and did not negotiate. but if you have an managed power source, at least you could get the port output power from its management interface.

for a general rule of thumb, check the power source switch per port power output, and make sure the wattage of the chaining device are satisfied. You shall found cascading seems impossible since typical 10W per port cannot support lots of devices. probably 4-5 is maximum.

by the way, for many passive device, it also draw power from computer LAN port, so make a dummy connection to a desktop computer is a good idea if you have encounter not-enough power situation. just make sure your computer support wake on LAN (idea: no need to enable, just make sure the LAN card still on while computer turn off)

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