802.3at vs 802.3af: Which PoE Standard to Use

Power over Ethernet (PoE) can feel confusing because it blends networking with electrical power. Most of us are used to plugging in a device and expecting it to “just work,” but PoE takes things a step further by delivering both data and power over the same Ethernet cable.

Originally, PoE was designed for low-power devices, such as VoIP phones. These phones were perfect candidates—they needed minimal power, a network connection, and often included an extra port for a computer. That efficiency reduced clutter and simplified workstation setups.

Why Use PoE? 

Although first used for VoIP phones, over time, PoE’s role has expanded. Wireless access points, security cameras, and even compact switches can now run over PoE, making it easy to install devices in ceilings, walls, or remote spots without nearby outlets. A nice bonus is remote rebooting—network admins can power-cycle devices just by toggling the switch port.

There are a few considerations, though. Your switches need enough power capacity (and redundancy) to keep devices online, and older cabling may need upgrades to support PoE reliably. For networks without PoE-capable switches, injectors provide a workaround, though they’re bulkier and less efficient than built-in PoE.

What is 802.3af?

The 802.3af standard is also referred to as simply PoE. This is because it is the initial PoE standard. It allows for a maximum of 15.4 watts. Devices that consume at this wattage or less are type 1 devices. This standard was a great start and, at the time, provided more than sufficient power for most devices. 

A huge benefit for type 1 devices is the power requirements. Because these have the lowest power requirements, that equates to lower capacity power supplies and circuits to the switches. In other words, it can be more economical. 802.3af devices are compatible with 802.3af and 802.3at switches. The downside to these devices is that functionality and features may be limited due to the limited power constraints.

What is 802.3at?

The 802.3at standard increased the maximum power to 30 watts, with 25.5 watts being the standard amount received by the device. According to CBT Nuggets trainer Kelvin Tran, "It’s both 30W and 25.5W. 30W [that] gets pushed by the device providing the power (the PSE) and 25.5W is, by standard, what is expected to be received by the device receiving the power (PD).”

This is commonly referred to as PoE+ or PoE Plus. Devices that consume at this wattage or less are considered type 2 devices. The major benefit is that this standard supports higher power needs for devices (type 2). For example, VoIP phones with LCD and video conference ability may fit into this.

Another benefit of this is that at the switch level, it supports type 1 and 2 devices as it is backward compatible with 802.3af. From a device perspective, 802.3at devices are likely to be more feature-rich, including color screens where applicable. 

The downside is that the increased power requirements could result in significantly higher power-related costs. Many times, power supplies require enough power that you may need one or more dedicated circuits for these power supplies. If you use a battery backup, higher-end backups are also needed. It can become difficult to supply the required power if you have many devices that require this increased power.

802.3at vs. 802.3af

It is not a matter of one versus the other. With 802.3at being the newer standard, on the switch side, it is backward compatible. If a port can only negotiate 802.3af due to the end device only supporting that, there will be no issues. 

On the other hand, if the end device requires 802.3at but the switch only supports 802.3af, it will not work since the device requires a newer standard and more power than the switch can accommodate. 802.3at compatible switches work quite well with 802.3af devices.

Cost Comparison: 802.3at vs 802.3af

The hardware price difference is noticeable between the different devices that you’ll come across, but devices that have special requirements need the right PoE solution to get the job done:

• 802.3af Switch Ports: $8-15 per port

• 802.3at Switch Ports: $15-30 per port

• PoE Injectors: $15-25 (802.3af) vs $25-45 (802.3at)

Things can get pricey quickly if you have a lot of PoE devices, but the savings from eliminating AC outlets could range from $150 to $300 per installation location. Your installation time also drops by a lot when you only need to worry about single cable runs for data and power.

802.3at or 802.3af: Which Should I Use?

The decision point is fairly simple. If you already have PoE-capable switches, many times, you can often determine the standard supported. In some cases, you can replace/upgrade line cards to support newer PoE standards. It is important to decide on the standards that your existing switching gear supports. Next, select the standards and power requirements of the devices you will be using.

Here’s a quick guide to help you decide which PoE you’ll need:

• Under 13W: 802.3af can handle it

• 13W to 25W: You will need to look at a 802.3at solution

• Over 25W: 802.3bt can do the heavy lifting for this power rating

If you don’t know what your device’s power draw is then you can search for the spec sheet for the product and see what its power requirements are. If you can’t get that info, then a general rule of thumb is that if you see PoE+ mentioned anywhere, then you will need at least 802.3at. 

If you want to learn more about these standards, and networking in general, then check out the CBT Nuggets IT Certification Matrix to help you get there. If you aren’t sure exactly which IT path you’d like to follow, then try out the new CBT Nuggets IT Personality Assessment Tool. Use it to help you figure out what you enjoy doing, and where you can put your skills to good use in the job market.

PoE in 2025: It's Not Just for Phones

PoE is used for many different kinds of devices, from IoT sensors to Wi-Fi hardware. Both  802.3at and 802.3af have wider use cases, and here are some examples:

IoT and Smart Building Sensors

• Environmental monitors like CO2 and air quality devices find 802.3af sufficient for power and communications.

• Advanced multi-sensor units with displays usually need 802.3at. 

• Digital signage (10-21-inch displays) will use more power, so 802.3at will be required. 

Modern Security Applications

• Basic IP cameras and 802.3af works for most, depending on how much power and bandwidth they need. 

• PTZ cameras with night vision and heaters will need 802.3at to power everything up. 

• High-resolution 4K cameras with bigger storage and processing will often need 802.3at to supply consistent power.

WiFi Evolution Impact

• WiFi 5 access points can use 802.3af PoE, and it's good enough to keep things running smoothly. 

• WiFi 6/6E access points are starting to use 802.3at as their default. 

• Most WiFi 7 access points require a minimum of 802.3at, with some even needing 802.3bt supplies—but this varies from device to device, so you will need to verify the PoE requirement for your specific device. 

Beyond 802.3at

802.3bt type 3 and type 4 have hit the market, and they have some pretty impressive specs:

• Type 3: 60W to the switch, and 51W to the device

• Type 4: 90W to the switch, and 71.3W to the device

Newer devices that have emerged in recent years require more power. Some examples where these newer PoE standards are being used are LED lighting systems with programmable RGB color modes and digital signage with higher power requirements. 

Remember to check the PoE requirements when you are upgrading your hardware so that you get the power and performance that you need to have a reliable setup.

802.3at vs 802.3af: Frequently Asked Questions

Can PoE Damage Non-PoE Devices? 

No, IEEE-compliant PoE is very safe for devices. 802.3af, 802.3at, and 802.3bt all use detection protocols before supplying power. The switch tests at low voltage (2V-10V) to check that the device is compatible before switching to full power.

What's the Maximum Distance for PoE? 

The maximum distance is 100 meters (328 feet) for all PoE standards and Ethernet cable specs, not power, limit it. PoE extenders can push this to 4000 feet, but Ethernet performance could drop to 100Mbps.

Will an 802.3at Switch Power 802.3af Devices? 

Yes, 802.3at switches automatically detect and provide the right power level for 802.3af devices through something called power negotiation.

Final Thoughts

When possible, choose 802.3at switches—they support both type 1 and type 2 power requirements while meeting most business needs. On the device side, aim for the most power-efficient models you can, and limit higher-draw devices to employees who truly need them.

If your setup requires more power, the newer 802.3bt standards (types 3 and 4) can handle heavier loads without additional cabling. Just keep in mind that once power demands push your hardware to its limits, switches and line cards may throttle or shut down ports to conserve energy. Staying power-conscious will help you avoid surprises.

Want to learn more? Cisco is one of the biggest names in PoE enterprise environments, making it a natural fit for IT professionals learning about PoE. 

Check out our Cisco Certified Network Associate (200-301 CCNA) Online Training to learn more.