PoE (Power Over Ethernet) is used in IP CCTV systems to supply power to connected IP cameras using CAT5 cable. Most wired IP cameras are PoE enabled. PoE enabled cameras can also be powered conventionally. Wireless IP cameras are not PoE enabled.
PoE enabled IP cameras require a 12v DC supply and around 5 Watts power. Cameras with heaters and/or motorised functions (PTZ) will require more power and may require a different voltage. When using PoE the voltage and power required are immaterial - the PoE enabled camera automatically grabs its required voltage and power. The output from a single standard PoE port is 48v with 15 watts available.
There are two standards for PoE - commonly termed standard PoE and PoE+.
PoE is the 802.3af standard, and PoE+ is the 802.3at standard. The main difference between the 802.3af (PoE) and 802.3at (PoE+) standards is the maximum amount of power they provide over the Cat5 cabling. The maximum amount of power for the 802.3af (PoE) standard is 15.4 watts. The maximum for the 802.3at (PoE+) standard is 25.5 watts. In relation to CCTV systems, standard PoE has plenty of capacity to power IP cameras. It should also be noted that the maximum recommended distance that PoE can be used is 100 metres At this 100m distance the actual power available drops to 12.95 watts. This can be extended by the use of intermediate PoE injectors: indeed it can be advantageous from a cable management point of view to have the PoE source remote from the NVR.
When purchasing a PoE switch you should be aware that there are two ways of specifying the power distribution as follows.
- Guaranteed per Port - this guarantees that each port will have the full amount of power available at each port.
- Total Power Budget - this just states what total power the unit can deliver across all the ports.
In surveillance CCTV systems using standard cameras either of the above will be sufficient. However for other uses such as Wireless Access Points, then the power will need to be managed correctly.
Also note that when a port is not used, there is no power taken by that port. A PoE port can be used as a standard data port without causing any damage to the equipment connected.
It is possible to use the power from a PoE port to power a non-PoE camera, but this requires the use of a dedicated splitter - you cannot simply splice the power cores out of the CAT5 cable - it is 48v and would likely 'fry' a 12v camera connected.
NVRs and PoE
NVRs (Network Video Recorders) are available with or without on-board PoE ports.
NVRs without on-board PoE ports may have either a single RJ45 network connection or individual npn-PoE ports for cameras. In order to use PoE, a PoE switch needs to be connected to the network connection on the NVR. For example a 4 channel NVR will need a 6 port PoE switch with at least 4 of those ports PoE enabled. The 4 PoE ports are used to connect the cameras, one of the 2 remaining ports connects the NVR to the switch and the remaining port connects the switch to the network - typically the internet.
It should also be noted that a relatively inexpensive non-PoE switch can also be connected and cameras can be connected to it. In this case the cameras will need to be powered either locally via a power supply or by using a PoE switch sited remotely and connected to the non-PoE switch. The possible combinations are numerous and is a good indication of how versatile IP CCTV systems are.
NVRs with PoE
The majority of NVRs are now supplied with PoE ports on-board. Commonly 4 and 8 channel NVRs will have 4 and 8 PoE ports respectively. On 16, 32, 64 channel models the number of on-board PoE ports is usually reduced to 8. This is due to the fact that in such large systems it is unusual to bring every data/PoE cable back to the NVR. It is usually far more efficient to have remotely sited PoE switches.
It is important to work out how the power management will be used in IP CCTV systems, especially large systems.
Systems can use a mixture of non-PoE, and PoE enabled switches, but if the camera is powered by PoE then the last switch before the camera must be a PoE switch. PoE cannot be routed through non-PoE switches.
See the article Connecting IP CCTV Systems.