PoE is a technology that allows network cables to deliver electrical power to devices connected to the network, in addition to handling data communication. With PoE, electric current is transmitted along with data on Ethernet cabling.
This allows devices that require power, such as wireless access points, IP cameras, and VoIP phones, to receive power over the same Ethernet cables that transfer data to and from the devices.
By providing power over existing cabling, PoE eliminates the need for additional electrical wiring and outlets to power network devices.
This provides cost savings, flexibility, and ease of installation for a wide range of business and home applications.
Since its introduction in the early 2000s, PoE has evolved through several standard updates to increase power levels and efficiency. It provides a convenient way to power IP-connected devices without local power access.
How PoE Works?
PoE utilizes Ethernet cables with four differential pairs of copper wires. In normal Ethernet operation, only two of these four pairs are used for data transmission.
PoE takes advantage of the spare wire pairs to deliver direct current (DC) power in addition to data. The positive and negative poles of the DC loop across the spare wire pairs.
PoE uses a standardized process between Power Sourcing Equipment (PSE) and Powered Devices (PDs):
- The PSE, typically an Ethernet switch, first detects if a PD is connected and determines how much power it needs.
- The PSE then begins supplying the required level of DC on the spare wire pairs without interrupting data transfer.
- The PD accepts the power over the spare wires while transmitting and receiving data over the regular wires.
This enables seamless power and data delivery over standard Ethernet cabling.
There are several PoE standards that define different power levels and technical specifications:
- PoE (IEEE 802.3af) – Provides up to 15.4W of DC power over Ethernet. Released in 2003.
- PoE+ (IEEE 802.3at) – An update to provide up to 25.5W of power. Uses all four wire pairs. Adopted in 2009.
- 4PPoE (IEEE 802.3bt) – Introduced in 2018, it uses all four pairs to provide up to 71W of power. Requires CAT5e or higher grade Ethernet cable.
- UPoE (IEEE 802.3bt) – Proprietary method to deliver up to 95W over standard Ethernet cabling. Not formally IEEE approved.
Higher power levels enable support for more powerful devices like security cameras, LED lighting, and thin clients.
The main components that enable PoE are:
- PSE – Power Sourcing Equipment. The PSE injects power into the Ethernet cable. This is typically an Ethernet switch, router, or injector that supplies power.
- PD – Powered Device. The PD accepts power over the Ethernet cable, like IP phones, wireless APs, cameras, and other endpoints. Needs to be PoE compatible.
- Ethernet Cabling – Requires CAT3 cable or higher for PoE. CAT5e or greater is recommended for best performance.
- PoE Injector – Can add PoE capabilities to non-PoE Ethernet switches. Injects power into an Ethernet cable similar to PSE.
Key applications and devices that utilize PoE include:
- VoIP Phones – PoE powers office VoIP phones, no AC outlet is required at each desk.
- Wireless Access Points – Conveniently powers WiFi APs installed around office buildings.
- IP Security Cameras – PoE cameras can be installed anywhere without needing local power.
- Point of Sale Systems – Eliminates extra power cables to POS kiosks and terminals.
- Lighting – LED lighting can be controlled and powered via PoE.
- IoT Devices – Connected sensors, badges, and hardware can be powered over Ethernet.
- Thin Clients – Powers virtual desktop thin clients and zero clients.
Some of the main benefits PoE provides include:
- Single cable for power and data – Reduces cabling requirements. No need for separate power lines.
- Flexibility – Devices can be placed without regard for proximity to power outlets.
- Cost savings – No electrician is needed to provide local power access. Saves on AC wiring and outlets.
- Reliability – Centralized backup power keeps PoE devices up longer than local AC power.
- Scalability – Can easily add more PoE ports via switches. Supports moves and adds.
- Energy efficiency – Centralized AC to DC conversion is more efficient than individual adapters.
- Speed of deployment – Faster installation by eliminating AC power coordination.
Some limitations and challenges of PoE include:
- Distance limits – PoE power levels degrade over long distances. Typically limited to 100m cable runs.
- Power availability – Total PoE power budget per switch is limited. Higher power requires updated switches.
- Compatibility – PD devices must support PoE and the same standard as the switch.
- Heat dissipation – Delivering power over cable generates some heat. Requires planning.
- Higher costs – PoE switches cost more than non-PoE switches. Power injectors add cost.
- Voltage drop – Some voltage drop and power loss occur during transmission.
- Standardization – Proprietary variations can cause interoperability issues.
Power over Ethernet provides expanded capability and convenience by delivering power and data over standard network cabling.
This allows greater flexibility in deploying devices without local power access while reducing infrastructure costs.
PoE has progressed through standards updates to improve power levels and energy efficiency. It enables simpler, scalable, and cost-effective approaches for powering a wide array of networked devices and IoT applications.
Understanding PoE’s capabilities and limitations helps IT professionals effectively utilize this technology across a wide range of business and residential environments.
Frequently Asked Questions (FAQ)
Ques 1: What type of Ethernet cable is required for Power over Ethernet?
Ans: Power over Ethernet requires a twisted-pair Ethernet cable of Category 3 or higher. CAT5, CAT5e, and CAT6 cables are typically used for PoE.
CAT5e cable or higher is recommended to reliably support PoE based on its twisted-pair design and quality.
Ques 2: What happens if a non-PoE-capable device is connected to a PoE port?
Ans: If a non-PoE-capable device is connected to a PoE port, no damage will occur. The Power Sourcing Equipment will detect the absence of PoE functionality and refrain from sending power through that port.
This avoids any risk of damaging equipment not designed for PoE. The port will function normally for data transfer.
Ques 3: Can you increase the length of a PoE connection beyond 100 meters?
Ans: The 100-meter distance limitation for PoE over twisted-pair Ethernet cable can be extended by using Ethernet repeaters or switches as relay points.
The repeater’s power and regenerate the PoE signal. Adding repeaters along the line in 100-meter intervals enables transmitting PoE over longer runs. Fiber optic Ethernet cabling also enables extending PoE further.
Ques 4: What happens if a device draws more power than a PoE switch port provides?
Ans: If a powered device attempts to draw more power than the Power Sourcing Equipment switch port allocates, the port will enter power-limiting mode.
It will restrict the power to the maximum level programmed for that port to avoid overloading.
This will lead to the powered device shutting down or operating in a degraded state. Proper planning is necessary to ensure each PoE device’s needs are within the supplied port’s capabilities.
Ques5: Can standard non-PoE switches be upgraded to support PoE?
Ans: Non-PoE Ethernet switches cannot be upgraded directly to support PoE, which requires integrated circuitry.
However, PoE capabilities can be added to non-PoE switches using intermediate PoE injectors.
The injector sits between the switch and the powered device to add PoE support over that connection. This is a simple way to extend PoE functionality to legacy or non-PoE switches.