Power over Ethernet and Power over Ethernet Plus can provide some significant benefits to a security installation.
There are however, some key points that need to be taken into account for a smooth deployment.
Therefore, what exactly is Power over Ethernet and when should we use it?
What is Power over Ethernet?
Power over Ethernet is a technology where spare pairs of an ethernet cable are used to deliver power to a device.
Ethernet cable is comprised of four twisted pairs of cable.
They are twisted to reduce interference and carry communications signals over distances of up to 100m.
Whilst we have four twisted pairs, only two twisted pairs are required for data communications.
This leaves two pairs available for other purposes, in this case, delivering power to the end device.
What difference does it make to an M&E Consultant?
As long as the device is powered and the network works, why should I care?
Everything still works, however, we can draw some benefits from powering security devices over the network.
The main benefit is fewer power spurs, power supplies and cabling.
These reductions alone can save a lot of time and money and reduce the overall complexity of the installation.
This is an important thing to consider when value engineering comes along during the latter stages of a project.
Two main standards
Whilst commonly referred to as Power over Ethernet, there are currently two main standards – Power over Ethernet and Power over Ethernet Plus.
Power over Ethernet
Power over Ethernet or PoE is the first standard, governed under IEEE 803.3af.
POE has the capability to deliver a maximum of 15.4 watts of power through a single data connection.
This allows devices such as cameras and door access controllers to be powered without requiring separate power supplies.
In most cases, however, the locks still required their own local power supply at the door, due to the higher power draw from most locks.
Power over Ethernet Plus
Power over Ethernet Plus or PoE+ is a newer standard, based on PoE, but provides a maximum of 30 watts, nearly double the available power per port of PoE.
With the use of an electrically operated solenoid lock, we can now support two card readers, an access control unit and lock from a single PoE+ feed.
There are four important aspects, which must be considered before specifying PoE or PoE+ for every project.
With a traditional, non-PoE installation, there will generally be local batteries in the power supplies near each door to maintain power to the access control equipment and locks if the power fails.
In a pure PoE solution, the power is coming from the network switch, not from local power supplies.
Unless the system integrator is providing and fully installing a network purely for security, someone else is responsible for ensuring that the system remains powered.
It’s vital when using PoE or PoE+ that battery backup is made available for network equipment to ensure the system remains operational in a power cut.
Each switch has a power budget, this is a maximum amount of power that the switch can provide to remote devices.
This doesn’t necessarily mean that we can fill up a switch with devices that require power and everything will work.
Careful planning is required to ensure that we do not exceed switch power budgets now or in the near future.
For example, if the security specification requires 20% spare capacity system, we also need to ensure that there is 20% spare capacity on switches.
Each switch will have a manufacturer specified switch budget.
in this example; we will use an 8 port PoE+ switch with a power budget of 180 watts.
If we divide the total power budget by 30 watts (the theoretical maximum per port for PoE+, we can expect to power a maximum of 6 ports at full PoE+ capacity.
In reality, we would look at each device we plan to connect to the switch and determine the power budget required for the total number of devices we plan to connect.
Using PoE and PoE+ means we are using Ethernet cables, this means we need to stay within the Ethernet limit of 100m.
Optical fiber is required for communications distances over 100m, but traditional power will be required.
PoE Switch Capability
It may be that we need to install equipment into an area where there are no PoE capable switches.
Replacing the switch is an obvious step and one that may work out financially neutral compared to installing traditional power.
If however, there are only a couple of devices, it may be better to install a power injector.
These devices attach to the network cable inline between the switch and the device being powered.
We plug the injector into a power socket and it sends power down the Ethernet cable to the remote device that requires power.
Power injectors, like switches, also need to be protected in the event of a mains power failure.
Question: What will you use on your next project and why? Let me know in the comments below.