Selecting a PoE Switch

You just picked up some new Power over Ethernet devices – a few of the hottest new IP cameras. However, after opening the box you run into a series of unexpected problems. No its a really powerful decision.

First: Each camera comes equipped with its PoE injector capable of supplying the appropriate level of power.  However, prior to even mocking up your panel it becomes clear – four PoE injectors and a standard Ethernet switch will not fit.
In an effort to maintain a reasonable panel size, you ditch the PoE injectors in favor of a Power over Ethernet switch, a single product that will replace all four injectors and provide Ethernet switching.  So far so good.

Second: After deciding that a PoE switch will best suit your need, you set out on a search for the cheapest PoE switch you can find.  Before long you realize the injectors were provided so that the cameras receive the exact amount of power they are optimized to run at.  With this new concern in mind, the search moves from the “cheapest switch” to the ”right switch.” In order to identify the right switch, you will need some information… but where do you look?

You are able to find a small label printed on the bottom near the Ethernet port of the camera – something that specifies how this camera can be powered. Now you have some numbers to shoot for, but what exactly do they mean?

While listed on the label in the above order, Power over Ethernet is best addressed in this order:-

1.     Is this a Power over Ethernet device?

A.     Will the device accept Power and data through the Ethernet port? Has the device been designed to make use of Power over Ethernet.

2.     Is this device IEEE 802.3af or IEEE 802.3at compliant?

A.     How much power will the device draw? Both IEEE 802.3af and 802.3at are based off +48VDC voltage but differ in wattage.

B.     IEEE 802.3af = “Standard PoE” = devices consuming up to 12.95W of PoE power IEEE 802.3at = “PoE Plus, High-Power PoE” = devices consuming up to 25.50W of PoE power

3.     Which class of Powered Devices (PD) is the device a member of?

A.     PoE capability and power level compliance – the class level of Powered Devices further specifies how much power the device will draw

Class 1 = 0.44 – 3.84W “Very low power”
Class 2 = 3.84 – 6.49W “Low power” 
Class 3 = 6.49 – 12.95W “Mid power” 
Class 4 = 12.95 – 25.5W “High power, suitable only for IEEE 802.3at PoE”

Translating the above power label again we find:

1.     Is this a Power over Ethernet device? Yes, this camera can accept PoE

2.     Is this device IEEE 802.3af or IEEE 802.3at compliant? IEEE 802.3af – the maximum it will draw is 12.95W at 48VDC

3.     Which class of Powered Devices (PD) is the device a member of? Class 2 – this device will draw between 3.84 and 6.49W – it is a “low power” device

After finding a Power over Ethernet switch that will provide suitable power conditions on a per-port basis, there is one final element to consider – power budget.

Will the switch you choose provide enough power per port for each camera? You bought four cameras to use four cameras, not to use just one or two.  Your choice in a Power over Ethernet switch needs to reflect this… Will the switch provide suitable power to all ports at all times?

Finally, after considering space in your panel, power demands of one camera, power ability of a switch for one port, and powering ability of a switch across all ports, you are prepared to make a decision!

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