Power over Ethernet (PoE) technology has revolutionized network deployments by enabling both power and data transmission over a single Ethernet cable. This simplifies cabling, reduces infrastructure costs, and offers greater flexibility in device placement. For network engineers, IT admins, and SMB IT buyers, understanding the PoE switch power budget, PoE power output, and PoE wattage per port is essential for efficient network design and operation.
What is PoE Power Budget?
The PoE switch power budget is the total power capacity that a PoE switch can supply to all connected Powered Devices (PDs). This overall capacity is critical because actual power consumption depends on various factors:
The number of switch ports
Types and number of connected devices
The switch model itself
For example:
An Aruba Instant On 1930 24-port switch consumes about 20 watts for the switch itself.
An 8-port PoE switch might use around 7 watts, while a 48-port switch can consume over 200 watts.
A basic unmanaged 8-port switch might consume 4 watts, with each connected PoE device adding roughly 6 watts. Four such devices could lead to around 28 watts total (4W + 4×6W).
The number and power demands of connected PoE devices are the biggest factor affecting the total power consumption.
How PoE Power is Distributed
PoE switches act as Power Sourcing Equipment (PSE), supplying power to devices like IP phones, surveillance cameras, wireless access points, and PoE lighting. The power delivery process typically involves:
Detection of Powered Devices: The switch sends a low voltage and detects if the connected device supports PoE via a 24.9kΩ resistor.
Classification: The switch measures the current to classify the device’s power needs (Class 0 to Class 8).
Power Delivery: Voltage is ramped up to a stable 48V DC for the device.
Normal Operation: The switch continuously supplies power while monitoring for faults or overloads.
Power Removal: If the device disconnects or power limits are exceeded, the switch cuts power to protect devices.
PoE power can be delivered via Mode A (data pairs), Mode B (spare pairs), or 4-pair delivery for higher power standards.
Typical PoE Wattage Per Port
The IEEE standards define power limits for PoE devices. Note that some power dissipates over the cable, so PDs receive slightly less than the switch supplies.
PoE Standards Overview
Ethernet cabling standards limit PoE distance to 100 meters, regardless of power delivery.
IEEE 802.3af (Type 1): Up to 15.4W per port, common for basic PoE devices.
IEEE 802.3at (Type 2): Up to 30W per port, backward compatible with 802.3af.
IEEE 802.3bt (Type 3 & 4): Supports up to 60W and 100W per port respectively, using all four pairs for higher power.
Ethernet cabling standards limit PoE distance to 100 meters, regardless of power delivery.
How to Check PoE Power on Cisco Switches
To monitor PoE power on Cisco switches, use the following CLI commands:
show power inline
show power inline detail
These commands display per-port power consumption, total available power, and any fault conditions. Refer to Cisco's official documentation for additional configuration guidance.
FAQs
Q1: What affects a PoE switch’s power consumption?
The number of ports, connected PoE devices, their power needs, and the switch model all impact total power usage.
Q2: Can a PoE switch adjust power to connected devices automatically?
Yes. Standards-compliant switches detect device capabilities and deliver appropriate power according to IEEE classifications.
Q3: What if a non-PoE device is plugged into a PoE port?
The switch will only deliver data, not power, ensuring no damage to non-PoE devices.
Q4: Is there a distance limit for PoE?
Yes, PoE is limited to 100 meters (328 feet) over standard Ethernet cabling.
Q5: Why use PoE switches?
PoE switches reduce cabling complexity and cost, simplify deployments, provide centralized power control, and enable scalable designs.
Conclusion
Understanding the power capabilities of your PoE switch helps prevent underpowered devices and ensures reliable performance. Whether deploying IP surveillance, wireless access points, or VoIP phones, always assess your power budget and device requirements before choosing a switch.
Need help selecting the right PoE switch? Visit router-switch.com for enterprise-grade Cisco, HPE, Aruba, and Huawei switches that meet your deployment and budget needs.
