How to budget power on your Poe switch

So you wanna take over the world with your camera installation right? but unbeknown to you, power over ethernet or POE as you may call it, is not as plug as play as you  may assume it is. Sure if you are using class 1 devices, the average POE switch should survive a fully populated installation but what if you are using one of these fancy class 3 devices? By now you should be asking what are these classes im referring to……

Active POE refers to intelligent POE, it MUST follow a standard either class 1, class 2, 802.3af or 802.3AT

  • Class 1 –     4.5 watts at PoE port, 3.84 watts at device
  • Class 2 –     7.5 watts at PoE port, 6.49 watts at deviceEC-ECS2000-26P_large

IEEE 802.3af

  • Class 3 –    15.4 watts  at PoE port, 12.95 watts at device
  • Class 0 –    15.4 watts  at PoE port, .44 to 12.95 watts at device

IEEE 802.3at

  •  Class 4-     30 watts  at Poe port, 25.5 watts at device

Passive POE does not follow these standards, what you put in is exactly what you get out, so if you take a 48V passive POE injector and try to power up a 24V device, say goodbye to your device. Passive POE does not test to see if the device to be powered actually wants POE, it forces the voltage to the device which can cause damage if the device is not compliant. Passive POE injectors offer a cheaper alternative for Power over Ethernet but more care must be taken when implementing it. The injector voltage must match the device voltage requirement.

Now it would be nice to know where your POE device is, in terms of these classes since POE switches are very much like Eskom, they only have so much power to give and if you over populate one exceeding it’s power budget, you will be introduced to load shedding but instead of your lights being out, your device will not light up.

How do you make sure this doesn happen? Easy! Firstly find out what the power budget of your switch is, I am going to use our very own Edgecore EC-ECS2000-26P which offers a 190w budget. Now tally the equipment you are connecting to it. How many watts do they need? Lets assume we use 5x the Vivotek IP8362. These are classs 3 devices meaning they operate at more than 7w but do not consume more than 13w. In actual fact they only consume a max of 10w (check the data sheet!). So you actually only need 50w to run your cameras. Since this is within your 190w budget, you will have no issues.

So how many cameras can you actually connect to this switch if they need 10w each? 190/10 = 19 IP8362 cameras.

So in essence, work out the consumption of your equipment and ensure it is within the rated power budget of your poe switch. This will ensure that when the device needs more juice, it doesn disconnect from your network. You also need to be aware of the maximum amount of watts per port your switch is capable of. The Edgecore 26P will offer up to 30 watts per port but!!!! remember our 190w budget? That means we can only offer 30w of power to 6 ports. (190w/6)

Feel free to contact if you have any questions


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