The Growth of Power over Ethernet (PoE)

Power over Ethernet (PoE), provision and use, has become a commonplace feature. Employed as a means to simplify the building of networks and the integration of service based hardware.  Such examples being IP phones, wireless access points and CCTV cameras. Indeed many manufacturers of data network equipment are now seeing sales of PoE compatible devices outstrip those of their non-PoE equivalent models.

There is a case for deploying PoE wherever possible. The small increase in initial hardware cost can be quickly offset in terms of the reduction in the number of alternate supplies that would need purchasing. With the speed at which new services can be deployed, once PoE is available to a business, greatly increased.

The Basics of PoE

The term “Power over Ethernet” refers to the use of Ethernet data cabling to carry electrical power. Allowing devices such as IP phones to receive their power and communicate with other devices via a single data network connection. The standard that covers basic PoE functionality is the IEEE standard 802.3af which describes and dictates how devices must behave. A powered device (PD), such as a phone or wireless access point receives power from the power sourcing equipment (PSE), typically an Ethernet switch. Although ‘mid-span’ PoE injectors can be used instead.

Not all devices, and personal computers fall in to this category, are designed to receive power over the Ethernet cable. So the standard includes a checking procedure whereby devices are required to confirm their need, through the presentation of a predefined signature, before the power is switched on.

The standards for PoE ensure users can guarantee the safety of the equipment they connect to networks.

Power over Ethernet

The Advantages of Power over Ethernet

The benefits of using PoE become apparent once the technology is understood. With the most common being the savings that can be made in electrical installation costs. No longer is there a need to run power cables around a building;  putting in large numbers of electrical sockets. A single installation of Cat5 Ethernet cable with sufficient numbers of familiar, standardised, RJ-45 termination points can be fitted instead. The PSEs supply power at a typical voltage of 48V DC which is high enough to be carried efficiently over the data cabling, whilst being low enough to be safe.

As mentioned previously the signature detection pattern built in to the IEEE802.3af standard prevents damage to non-compatible equipment. Allowing a PoE enabled network switch to be used, risk free, with non-PoE devices. In addition, the continuous current monitoring function can be relied upon to disconnect power from a malfunctioning powered device (PD) if it begins to draw too much power from the switch. Power delivery will also be turned off as soon as a PD is disconnected and only turned back on again when it, or a replacement device, is plugged back in.

The use of PoE allows businesses to be more sophisticated in terms of device control and power management when implementing new networks or upgrading existing ones. In most cases the power to many network devices will be routed through a single wiring cabinet. Installing an uninterruptible power supply (UPS) will maintain power delivery to critical network equipment, even during short outages. This can be extremely beneficial in keeping businesses in a ‘trading state’. Preventing them from becoming disconnected from the outside world, their suppliers, and most importantly their customers.

Limitations of Using PoE

The primary limitation of using this technology is the restricted distance over which it can be supplied. Ethernet cable can only be pulled to 100m in length. So any equipment that needs to be supplied power over a single cable beyond this distance would not be able to be supplied from the central wiring cabinet.

There are solutions to this problem however. In a similar fashion to their being repeaters for data signal regeneration, allowing transfer beyond 100m, so there are inline devices that can be installed to regenerate the power fed to PD equipment. As well as boosting the data signal.

Whilst careful design is required to identify problem areas, like the one described above, it is still possible to demonstrate good cost savings by introducing PoE switches. The case for deploying PoE is compelling.


The use of Power over Ethernet has been proven to introduce a host of technical benefits and long term cost savings for businesses as they renew, or introduce brand new, end to end communications infrastructure. It contributes to simple, elegant, data network design and is a fundamental building block used by the Stamford Telephone Company in the solutions we provide our end customers.

Its universal availability provides a strong case for the transition to IP communications services, such as voice over IP (VoIP), and with BT withdrawing ISDN from the market place by 2025 reliable, good quality, hosted telephony solutions can be built today.

You can contact The Stamford Telephone Company by calling 01780 430490 or by filling out our Contact Form.