Power Over Ethernet - POE

POE, put simply, is the ability to carry the power to a network device using the network cable and no other.

The standard cat5 network cable contains four twisted-pairs. Only two of these pairs are used for data; a pair to transmit, and a pair to receive.

Plainly, there are therefore spare cores within the cable, and it is these that are used to carry the POE power.

Most network devices such as cameras operate at a low voltage, typically 5-12 volts.

To ensure that the POE power can travel a useful distance and still arrive at the camera with sufficient volts, the volts typically travel along the cable at 48 volts AC.

This achieved by the insertion of a device at the source end known as a power injector. Typically the data cable is routed through this power injecting device and effectively picks-up the 48 volts en-route.

This configuration, through a separate power injecting device, is known as a mid-span configuration.

The power injecting device can be a single unit to feed just one device at the far end of one cable or it may take the form of a multi-way (for example 8-port) hub-type device.

Furthermore, the injector may actually be integrated into a network switch, so that a single switch unit is able to connect multiple network devices onto the network AND inject the power to feed each of them.

This configuration, where a single device combining the data switch and power injection is used at the source end, is known as an end-span configuration.

At the device end, many modern cameras and similar devices are now supplied POE-enabled; this means that they are able to take the single network cable connection, and internally to the camera they split the power signals from the data signals.

Devices which are not specifically supplied as POE-enabled can still be fed via a single network cable using POE. All that is required is that an Active Splitter is placed adjacent to the camera. The active splitter will take the POE network cable carrying the power and will simply split the power and the data back to separate cables.

If you choose this option be very careful to select an active splitter which ultimately outputs the right voltage for your selected camera or other device. Most active splitters are switchable and allow you to select whether you wish to output 5, 9, 12 or even 15 volts, but you must select the correct voltage!

Of course, it goes without saying, that the major incentive for utilising POE is the ability to self-install. You are only running a network cable carrying low-voltage, it is designed to be safe. The power injecting devices 'look' for a load at the end of the cable, if there is no load they do not inject any volts.

Due to their inherently safe low-voltage POE supplies are also ideal to supply network devices outside the building. Up to now there has been a compromise in that camera housing heaters required more power than could be supplied via POE, but new low power entirely POE camera housings are coming soon.

There is also work in hand to amend the standards to enable more power; the current limit is around 15W, and they hope to increase it to 30W. The new standard will be called 802.3at, and will be ideal for pan,tilt, zoom (PTZ) cameras, where the motors to operate the axial movements need more power.

The IEEE standard 802.3af governs the parameters of Power Over Ethernet.

One common system solution which you might wish to bear in mind is to use a combination of POE and wireless networking, you can simply self-install a POE cable to a Wireless Access Point at a high position, which will allow you to further extend your network's reach wirelessly.

The final, icing on the cake benefit to consider, all of this low-power distribution, via network cables, from a central point - you only need to place a simple Uninterruptible Power Supply (UPS) at the centre of the system to keep the recording PC and the power injecting device fed with mains and you will have achieved a maintained CCTV recording solution far more easily than is ever possible with a mains-fed system.

If you need any help with selecting the correct product combinations, please don't hesitate to call or email us.