Power Over Ethernet (PoE)
What is PoE?

Power over Ethernet use with IP Security Cameras has added some very effective power options that have not previously been available in CCTV Security Camera Systems. This page will explain all about PoE and use with IP Security Cameras. If you prefer you can view our video training by clicking here.

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Power over Ethernet is defined across a single network link. The three basic components of a PoE connection are:

  1. The equipment that delivers power to the cable (often referred to as a PSE, which stands for power sourcing equipment)
  2. The device which receives its power from the cable (also known as a powered device, or PD)
  3. The cable itself

Typical PDs include IP security cameras, wireless access points (APs), etc., and the PSE would normally be a PoE enabled network switch or a midspan power injector, patched in to add PoE capability to a non PoE network switch channel or similar.

PoE devices use a "Power Classification" in order to identify the type of power that is needed. As a part of the start-up process when a PoE connection is made, the PD can "advertise" its power class, which is an indication of how much electrical power it requires to operate.

Class Min PSE Power Max PD Power Example PD
1 4 watts 3.84 watts VOIP telephone
2 7 watts 6.49 watts ip video camera
3, 4, 0 15.4 watts 12.95 watts wireless ap

Note also that these figures are upper limits to power. Power cannot be "forced" down the cable – a surprisingly common misconception. The PD simply presents a load to the cable and draws as much current as it needs. Most PoE-powered devices will draw a fixed level of power.

There are two kinds of POE Switches currently manufactured in the marketplace. There is the kind that operates with a "guarantee per port" and the kind that operates with a "total power budget".

Guarantee per port means that you can connect as many Class 3 or 0 devices and the switch will be able to power them. (15.4 watts each) They are more expensive, bigger in size and work better in a controlled (cooled) environment.

A total budget switch can only power as many devices as it has power to spare. For example if had a 4 port switch with total of 30 watts for the entire switch you could power four class 2 devices. (4 x7.5 watts = 30 watts) That is OK. Or you could power two class 3 devices. (2 x 15 watts = 30 watts) This is ok as well, however you would not be able to use the other two ports for PoE since the total budget for the switch is maxed out.

Power Over Ethernet in general is a very safe technology. There are a number of built in safety factors that make it that way. The first is signature detection. Meaning voltage can not be applied to the cable until a compatible PD has been detected. The classification can be detected even before the device is powered up. This prevents the wrong kind of voltage being applied to the device.

Then there is current limiting. Current limiting is employed to protect the PSE from overload and to quickly disable malfunctioning PDs. There is also polarity protection. Polarity protection provided by the bridges in the PDs power input circuitry means it can safely receive power regardless of the configuration and polarity of the voltage on the cable.You also have automatic disconnection of devices that is performed when the monitored current falls below a minimum level.Finally low voltages are used to protect installers from electric shock hazards. The voltage used by PoE (up to 57 volts) is high enough to be efficient but low enough to be safe.

Because of the low voltage POE is limited to about 300 feet. (100 meters) The distance can be expanded by products from a company like Veracity USA. With their Outreach devices you can extend the distance another 300 feet with each device.

A couple of the main advantages to PoE are the lower cost of installation. You only need a single cable for both power and data. The maintenance in a PoE installation is much easier as well. Finally you can provide a central power supply that will typically have UPS backup. So when power is lost in a building the CCTV Security Camera System will still be in operation.

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