Tuesday, January 16, 2007

Power over Ethernet for IP Cameras

You would think it was simple, but it's not. There's more to Power over Ethernet (or PoE) then meets the eye. Just so we are all on the same page, PoE is a way of providing power to a device on the network. For example an IP camera that connects to the network can be powered over the same cable that is used to provide network data. The power is provided using extra unused wires in the network cable. If a camera conforms to the IEEE 802.3af standard, PoE is easy, but if it doesn't things can get complicated. Many cameras whether they conform to the PoE standard or not can be powered over Ethernet.
Here's how to do it.

Power Requirements depend on the camera

In all cases, power (that's voltage and current) is sent over the extra network wires. The wires are not very heavy (gauge) so they limit the power available at the device. The way the power gets to the wire and the way it gets to the camera can vary. Not all cameras use the same voltage. Some use 5VDC, other 12VDC or even 24VAC. As I mentioned, there is also an IEEE 802.3af standard that defines the PoE voltage and current. Many new cameras conform to this standard, while many older cameras have an external connector where power can be plugged in. Cameras that are compatible with IEEE 802.3 can get their power through the RJ45 network connection.

The power required by the camera system determines if PoE can be used

Most IP cameras can use PoE, but there are some cameras that require too much current and can't be powered over Ethernet. PTZ cameras require the most current because their little motors use a lot of power. For example, the Axis 214PTZ and Axis213PTZ can be powered. Since they require more current they require a higher powered midspan. On the other hand the Axis 231D and Axis232D+ can not be powered with PoE because they exceed the current that can be carried over the Ethernet wires.

PoE is great for indoor applications. It allows you to use a single cable to connect the camera, which greatly simplifies the installation. When the camera is used outdoors in an environmental enclosure and a heater and blower is required, you can't use PoE to power the enclosure because it requires too much power. Installation is still fairly simple because you can use the same power that goes to the heater and blower to power the camera.

If you plan to use a wireless camera, obviously you can't use PoE. I mention this only because we have actually been asked this question.

Power over Ethernet Solutions

Here are some details on how power is provided over Ethernet. Power is inserted to the network wire going to the camera using a powered network switch or a midspan (or power injector).

The power is connected to the camera either through the RJ45 network cable connection or using a special splitter that provides power to an external power connector on the camera.

Here are the solutions available:

Solution 1A: When you have an IEEE 802.3af compliant network camera you can use a PoE-enabled switch to provide the power. The camera uses the standard 48VDC power and uses the power from the RJ45 cable connection.

Solution 1B: If you have a IEEE 802.3af compliant network camera but do not have a powered network switch, you can add a midspan or power injector that complies with the standard. It's placed between the standard switch and the camera. Again the camera doesn't require any splitter because it uses the standard 48VDC power from the network connector.

If the camera is not compatible with IEEE802.3af standard, you will require a splitter at the camera side. An active splitter can be used to convert the voltage from the voltage injected (could be 12VDC or 24VAC or 48VDC) to the right voltage for the camera. If you have a powered switch that conforms to the standard, the splitter will convert the voltage from 48VDC to 12VDC or 5VDC (depending on the splitter). You need to select the right splitter for the camera so that you get the right amount of voltage and current as well as the right connector.

There are two solutions available:

Solution 2A: When you have a Network camera that does not conform to the IEEE802.3af PoE standard and you have a PoE-enabled switch, you will need to add an active splitter that supports the standard power. The splitter has to be matched to the camera.

Solution 2B: When you have a Network camera that does not conform to the IEEE802.3af PoE standard, and have a standard (non-powered) network switch, you will require a midspan or power injector and an active splitter. In this configuration the midspan or injector could provide IEEE standard power or non-standard power (24VAC for example). As long as the splitter is compatible with the midspan and camera, it will work.

If you still have questions about PoE or need help selecting the right camera system, just go to my web site or contact me.


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