Power Over Ethernet (PoE) Explained: A Plain-English Guide for UK Businesses

Power over Ethernet (PoE) sends both data and electrical power down a single network cable. Instead of running separate mains power to every IP phone, security camera or wireless access point, one Cat5e or Cat6 cable does both jobs. For UK businesses installing new phone systems, upgrading security or adding enterprise Wi-Fi, Power over Ethernet can save thousands in installation costs.

How PoE works

PoE sends low-voltage DC power alongside data signals through the spare pairs in an Ethernet cable. Standard network cables have eight wires arranged in four twisted pairs. Traditional 100Mbps Ethernet only uses two pairs for data. PoE uses the spare pairs to carry 48V DC power from the switch to connected devices.

The power source sits at the network switch end. PoE switches inject power into the cable, and the connected device extracts what it needs. The system is intelligent. Devices negotiate how much power they require, and the switch only supplies that amount.

Plug a PoE device into a PoE switch port and it works immediately. No configuration needed.

PoE standards and what they deliver

Several PoE standards exist, each delivering different power levels. The original IEEE 802.3af standard from 2003 delivers 15.4 watts per port. PoE+ (802.3at) bumps this to 30 watts. The newest standard, PoE++ (802.3bt), can deliver up to 90 watts per port.

Most business applications fall into the first two categories. IP phones typically need 5-7 watts. Basic wireless access points use 10-15 watts. High-performance Wi-Fi 6 access points might need 25 watts. Security cameras with pan/tilt/zoom functions can draw 20-30 watts.

Cable type matters too. Cat5e handles standard PoE and PoE+ without problems. For PoE++ applications drawing more than 30 watts, you need Cat6 or better to handle the higher current safely.

What most businesses power with PoE

Three device types make up 90% of business PoE installations: IP phones, wireless access points and security cameras.

IP phones are the most common PoE device. Every desk phone in a modern VoIP system runs on PoE. This eliminates power adaptors at every desk and makes moves and changes simpler. Someone changes desk? Unplug the phone and plug it in elsewhere.

Wireless access points almost always use PoE. Ceiling-mounted Wi-Fi access points are often installed far from mains outlets. Running PoE to the ceiling via structured cabling is much cleaner than having power adaptors in ceiling voids.

IP security cameras increasingly use PoE, especially in commercial installations. External cameras on building perimeters can be powered and connected with a single cable run back to the comms room. Fewer external power supplies means fewer failure points.

Installation cost is where PoE pays off

The big advantage of PoE is installation cost, not running cost. Every device that doesn't need a mains connection saves you an electrical installation. For a 50-person office with IP phones on every desk, that's 50 fewer power outlets and electrical runs.

Electricians charge £100-150 per additional power outlet in commercial buildings. Multiply that across dozens of devices and the savings add up fast. Ongoing power costs are nearly identical. PoE is about 10% less efficient than direct mains power due to conversion losses, but the difference is negligible.

PoE also reduces maintenance headaches. Centralised power management means fewer points of failure. When a power adaptor fails, you're hunting for the dead unit. When a PoE port fails, the switch management interface tells you exactly which one.

Choosing the right PoE switch

Not every network switch supports PoE. Standard switches only pass data. You need specific PoE switches to inject power into the cables. They cost more, but the premium has dropped significantly over the past five years.

A typical 24-port PoE switch suitable for small business use costs £400-800 depending on power budget and management features. Enterprise PoE switches with full PoE+ on all ports start around £1,200 for 24 ports.

The key specification is total power budget. A 24-port PoE+ switch might support 30 watts per port on paper, but only have a 370-watt total power budget. That means you can run 12 ports at full PoE+ power, not all 24. Plan your power requirements before specifying switches.

Where PoE makes the most difference

PoE makes sense when you're installing multiple network-connected devices in locations without convenient mains power. New office fit-outs are ideal because you can design power and data infrastructure together.

Retrofitting PoE into existing offices works well when you're already upgrading the phone system or adding enterprise Wi-Fi. The structured cabling installation can incorporate PoE-capable switches at the same time.

Warehouse and industrial environments benefit most. Wireless access points and security cameras in these spaces are often mounted where running mains power would be expensive or impractical. A single Cat6 cable can provide both connectivity and power to devices mounted 10 metres up on warehouse racking.

PoE is less useful for high-power devices. PoE++ can deliver 90 watts, but most devices needing that much power have other constraints that make mains power preferable.

Cabling requirements for PoE

PoE puts additional demands on your structured cabling. The cables carry more current than data-only installations, so cable quality and installation practices matter more.

Cat5e handles standard PoE and PoE+ without problems if properly installed. But if you're installing new cabling, Cat6 is worth the small premium for better heat dissipation and future compatibility with higher-power PoE standards.

Cable bundling requires more care. Large bundles of PoE cables generate more heat than data-only cables. Follow manufacturer guidelines on bundle sizes and use cable trays or basket systems rather than tight conduits where possible.

Connection quality is critical. Poor terminations that work fine for data can cause voltage drop and heat build-up when carrying PoE current. Use quality connectors and follow proper termination procedures.

Frequently asked questions

Common questions about Power over Ethernet for UK businesses.

Can PoE damage non-PoE devices?

No. Properly implemented PoE is safe for all Ethernet devices. PoE switches detect whether a connected device needs power before sending any. Standard network devices like computers and printers won't be damaged if plugged into PoE switch ports. The switch simply provides data connectivity without power injection.

How far does PoE work?

PoE works over the same distances as standard Ethernet: up to 100 metres for Cat5e, Cat6 and Cat6A cables. Voltage drop over long runs can reduce available power at the device end though. For runs over 75 metres, check that sufficient power reaches high-consumption devices like PTZ cameras or high-power access points.

What happens if a PoE switch fail?

All devices powered by that switch stop working immediately. IP phones, wireless access points, security cameras. For critical applications, consider uninterruptible power supplies (UPS) for PoE switches, or redundant switch configurations. Some businesses keep spare PoE switches configured and ready for quick replacement.

Do I need an electrician to install PoE?

No. PoE installation is low-voltage network work, not electrical work requiring qualified electricians. The PoE switches themselves need mains power connections, which must be installed by qualified electricians. The data cabling and device connections can be handled by network installation specialists.

Can existing Cat5e cabling support PoE?

Most existing Cat5e installations support PoE and PoE+ without problems, provided the original installation was done properly. The main concerns are cable quality, termination quality and total cable run lengths. A site survey can assess whether your existing cabling will support PoE devices reliably.