Power over Ethernet
Also known as: PoE, PoE+, PoE++, 802.3af, 802.3at, 802.3bt, powered Ethernet
Power over Ethernet (PoE) is a technology that delivers electrical power alongside data through standard Ethernet (Cat5e/Cat6) network cables.
Devices like IP security cameras, WiFi access points, VoIP phones, and smart building sensors can receive power through their Ethernet connection, eliminating the need for a nearby electrical outlet or separate power adapter. PoE-capable network switches (PoE switches) supply power through the Ethernet port; PoE-compatible devices draw up to 15.4W (standard PoE), 30W (PoE+), or 90W (PoE++) from the cable. PoE simplifies installation for devices in locations where running power wiring is expensive or difficult.
Power over Ethernet, explained at three levels
At home
Power over Ethernet means using the network cable (Ethernet cable) to deliver both internet data and electricity to a device at the same time. Normally, a WiFi access point or security camera needs two cables: one Ethernet cable for internet, and one power cable plugged into an outlet. With PoE, one Ethernet cable does both jobs. This is useful because Ethernet cables are much easier to run through walls and ceilings than electrical cables, and there's no need for an electrical outlet near every ceiling-mounted camera or access point. The power is supplied by the network switch at the other end of the cable.
At work
PoE simplifies and reduces the cost of network device installation in buildings. Without PoE, every IP camera, WiFi access point, and VoIP phone requires an AC power outlet nearby -- expensive to install in ceiling voids and wall locations. With PoE, a single Cat6 run from the network closet powers and connects the device. PoE also centralizes power backup: putting a UPS (uninterruptible power supply) at the network switch provides backup power to all PoE devices simultaneously, keeping cameras recording and phones working during power outages without individual backup batteries at every endpoint.
At home
PoE standards and power levels: IEEE 802.3af (PoE) delivers up to 15.4W per port (enough for IP cameras, VoIP phones, basic WiFi access points); IEEE 802.3at (PoE+) delivers up to 30W (WiFi 6 access points, PTZ cameras, video phones); IEEE 802.3bt (PoE++) delivers up to 60W (Type 3) or 90W (Type 4 -- laptops, digital signage, thin clients). Devices negotiate power requirements with the switch using LLDP (Link Layer Discovery Protocol) or resistor-based classification. A PoE switch has a total power budget across all ports -- a 24-port switch with a 370W power budget can supply approximately 24 devices at 15W average, but may only power 6 devices simultaneously at full 60W each.
At work
PoE switch power budget planning: deploying PoE infrastructure requires calculating total power budget needs across all powered devices. Each port can deliver up to its rated standard (15/30/60/90W) but the switch has a fixed total power budget. For example: a 48-port PoE+ switch with a 740W budget can power 48 PoE phones at 6W each (288W total -- well within budget) or 48 WiFi 6 access points at 25W each (1,200W -- exceeds budget, requiring either a higher-capacity switch or load distribution). The switch also draws internal power for switching functions. PoE infrastructure design requires summing device power requirements, adding 20-30% headroom for growth, and selecting switches with appropriate budgets.
At home
PoE injectors and splitters: a PoE injector is a small device that adds PoE power to a standard Ethernet connection from a non-PoE switch -- useful for adding PoE capability to specific runs without replacing the switch. A PoE splitter is the reverse: it receives PoE power and splits the signal into separate data (Ethernet) and power (DC barrel connector) outputs, enabling non-PoE devices to be powered by a PoE port by providing a separate DC power connection. These are useful for retrofitting PoE to existing installations or powering non-PoE devices like legacy IP cameras from a PoE switch without replacing the devices.
At work
PoE for smart building systems: PoE++ (90W) enables powering thin clients, digital signage displays, and LED lighting directly from the network. Cisco's Digital Building initiative and Cree's connected lighting use PoE for LED fixture power and data (enabling addressable, individually controlled lighting without separate 120V wiring). PoE-powered LED lighting integrates building controls (occupancy sensing, daylight harvesting) with network-addressable control -- each fixture is both a network endpoint and a lighting device. The advantages: single-cable installation, network-managed dimming and scheduling, straightforward firmware updates via the network, and UPS backup for emergency lighting. The limitation: 90W per circuit limits total luminaire power, constraining the approach to LED fixtures only.
Real-world examples
At home
Marcus installed a home security system with 6 IP cameras. Initially planned with wireless cameras, he switched to wired PoE cameras when he realized wireless cameras required battery changes every 2-3 months and had connectivity issues through walls. He ran Cat6 cable from a PoE switch in his home office to each camera location. One cable per camera provided both network connectivity and power -- no outlets needed at camera locations. The PoE switch in his office was connected to a UPS, so cameras continued recording during power outages.
At work
Nadia managed IT infrastructure for an office building renovation. The design included 120 WiFi access points, 80 IP cameras, and 200 VoIP phones -- all requiring power. Traditional design would require 400 AC outlets in ceiling and wall locations throughout the building. With PoE, she specified PoE+ switches in each floor's network closet (each closet already required Ethernet cabling infrastructure). Total power outlets eliminated: 400 (saving approximately $80,000 in electrical rough-in work). All devices powered by a centralized UPS in each network closet, providing 4-hour backup for phones and cameras during outages.
Common confusions
- Many people assume any Ethernet cable and any Ethernet switch can deliver PoE — PoE requires a PoE-capable switch (or PoE injector) -- standard Ethernet switches do not supply power through their ports. Additionally, the powered device must be PoE-compatible; connecting a non-PoE device to a PoE port is safe (PoE switches probe for compatible devices before applying power) but the device will not receive power. Cable quality matters for PoE: standard Cat5e supports PoE and PoE+; PoE++ Type 3 and 4 (60W+) require Cat5e at minimum and benefit from Cat6 for its lower resistance (which reduces heat and power loss in the cable at high current). Running maximum PoE++ current through long runs of thin-gauge cable can cause the cable to run warm and reduces delivered power.
- Some assume PoE devices are limited to low-power applications because Ethernet cables can't carry significant power — PoE++ (IEEE 802.3bt Type 4) delivers up to 90W per port through standard Ethernet cables -- enough to power laptops, 4K digital displays (low-power models), and commercial LED lighting fixtures. A standard Cat6 cable (24 AWG) can safely carry 600mA per wire pair; PoE++ uses all four pairs simultaneously, enabling 1,440mA at 50V = 72W delivered to the device (with some loss in the cable). For context, most thin-and-light laptops consume 45-65W charging while in use -- within PoE++ capability. The practical limitation is the switch's per-port and total power budget, not the cable's physical capacity.
For analysts
PoE is a relevant infrastructure consideration for any client planning or renovating physical space with networked devices: offices (VoIP phones, WiFi access points), retail (digital signage, IP cameras, POS terminals), healthcare (nurse call systems, WiFi for medical devices), education (access points, classroom displays), and smart buildings (sensors, lighting, access control). The cost analysis: PoE eliminates AC outlet costs for covered devices but increases network switch costs (PoE switches cost more than non-PoE equivalents). The breakeven typically favors PoE when more than a handful of devices are deployed in locations where electrical outlet installation is expensive (ceiling mounts, exterior walls, remote areas of a facility).
History & origin
The concept of powering devices over network cables predates formal standardization -- early proprietary implementations powered IP phones over Ethernet in the late 1990s. IEEE 802.3af (PoE, 15.4W) was standardized in 2003; IEEE 802.3at (PoE+, 30W) in 2009; IEEE 802.3bt (PoE++, up to 90W) in 2018. PoE adoption grew rapidly with the proliferation of IP cameras, WiFi access points (802.11n/ac/ax access points consume 10-25W), and IP telephony. Modern enterprise network deployments routinely use PoE switches as the power source for all edge devices in a floor or building, reducing electrical infrastructure costs significantly. The 4-pair PoE++ standard (Type 4, 90W) enables powering laptops, thin clients, and digital signage over Ethernet, eliminating the need for AC power at individual workstations in some deployments.