Power over Ethernet (PoE) allows you to supply both data and power through a single network cable, eliminating the need for separate wall outlets for devices such as ceiling access points (APs), doorbell cameras, and outdoor security cameras.
Overview of PoE
The idea behind PoE is simple: spare electrical capacity in an Ethernet cable can be used to send DC power alongside data. This means that devices placed in awkward locations can operate without the need for a separate power source, making installation easier and more flexible.
Standards and Budgets
PoE operates according to several standards with different power capacities:
- 802.3af (PoE): Up to ~13W delivered. Suitable for cameras, desk phones, and basic APs.
- 802.3at (PoE+): ~25W. Ideal for modern Wi-Fi 6 APs and PTZ (Pan-Tilt-Zoom) cameras.
- 802.3bt (PoE++, Type 3/4): 51-71W. Supports advanced devices like Wi-Fi 7 APs, video phones, mini PCs, and monitors.
Passive PoE
Passive PoE is a non-standard approach where power is always available on the cable, typically at a fixed voltage (e.g., Ubiquiti's historically used 24V or MikroTik's). This can be dangerous if connected to devices expecting standard PoE. Always check for compatibility: this is the "poE gotcha."
Safety and Negotiation
Standard PoE switches (PSE, Power Sourcing Equipment) are designed to ensure safety by probing electrically for a valid powered device (PD) signature before applying power. This negotiation process ensures that non-PoE devices remain safe; they simply won't receive any power.
Where the Power Comes From
- PoE Switch: A switch with multiple PoE ports, each capable of delivering up to its specified budget. For example, an 8-port PoE switch with a 65W budget cannot supply 8 cameras at 12W each. Budget math is crucial: this is the "budget gotcha."
- PoE Injector: A single-port device that adds power to one cable run. Useful when you need to power just one AP.
- PoE Splitter: A device that taps PoE power back out to a barrel jack or USB-C port, allowing non-PoE devices like a Raspberry Pi in the attic to operate on a single cable.
Practical Considerations
- Budget for Wire Loss: Devices may draw slightly more power than their rated capacity. For example, a 25W device might require ~30W at the switch.
- Cable Type and Distance: Cat6+ cables perform better with high-power PoE due to lower signal loss. The maximum distance remains 100 meters as per Ethernet standards.
- Resilience: Connecting a PoE switch to an Uninterruptible Power Supply (UPS) ensures that cameras and APs can ride through power blips, providing quiet resilience.
By understanding these principles, you can effectively deploy PoE in your home or office network for seamless device operation.