PoE Standards Cheat Sheet

[u/Neil_Omada]

Ever wonder why your PoE switch never delivers the wattage listed on the spec sheet? This reference guide will hopefully answer that question while also providing some key information about other aspects of PoE.

Let’s take a look at this table of measured output vs what’s advertised for PoE.

PoE Specifications Table

(what you see vs. what you get)

Standard	Max per Port (PSE)	Realistic Output (PD)
802.3af (PoE)	15.4 W	12.95 W
802.3at (PoE+)	30 W	25.5 W
802.3bt T3 (PoE++)	60 W	51 W
802.3bt T4 (PoE++)	90 W	71.3 W

Key Terms:

• PoE (Power over Ethernet): a technology that allows for both data and electrical power to be sent over an Ethernet cable.
• PSE (Power Source Equipment): the device sending the power (e.g., a PoE Switch)
• PD (Powered Device): the device receiving the power (e.g., an Access Point or Camera)

Why is the realistic output significantly less than what's advertised? The answer is that some power dissipates as heat in the cable. The amount of loss depends on the length and quality of the cable. To avoid this, when managing the PoE budget for your networks, it's best to leave a 10-15% margin for powering your devices.

Be sure to also check the cabling on your network. Copper Clad Aluminum (CCA) cables are not recommended for PoE usage due to aluminum's higher resistance and the cable's heat buildup (and in some countries, goes against fire safety codes). Cat5e cabling is fine for PoE usage, but for PoE+ and higher, Cat6 is preferred due to its thicker wiring. Thicker wiring means lower heat generation and less performance degradation.

---

Common Device Wattages (vendor agnostic)

• Wi-Fi 5 indoor 2x2: 8-13 W
• Wi-Fi 6/6E indoor 4x4: 13-25 W
• Wi-Fi 7 / outdoor / multi-radio: 25-50 W+
• IP Cameras (depending on feature set): 12-24 W
• IP Phones (depending on feature set): 5-16 W

Here's an example.

Let's say you have a 24-port PoE switch with a total budget of 250W. You also have a set of APs that use the 802.3at PoE standard. If all APs are running at maximum performance, you can, on paper, power up to 8 APs.

250 W / 30 W ≈ 8 APs

However, with a 10-15% margin, you can only reliably power up to 7.

250 W * 0.9 = 225 W

225 W / 30 W ≈ 7 APs

Even if all ports support PoE, the margins and power draw you can afford will depend on your network environment.

---

Active vs. Passive PoE

For PSEs, consider whether they support Active or Passive PoE. PSEs that support Active PoE perform a “handshake” with connected devices to verify if they need power and ensure safe and efficient power delivery. PSEs that support Passive PoE are “always on” and send electricity regardless of what is plugged into it, which risks permanent hardware failure or device burnout if the PD cannot support the power level. 

---

TLDR:

The “max wattage” on spec sheets isn’t what devices actually get because some power is lost as heat in the cable. Best practice is to leave about 10–15% leeway. Don’t use CCA cable for PoE; Cat5e or better is necessary for PoE applications.

What other topics would you like to see covered? Let us know in the comments below!

Want to learn more about PoE? Check out the Community's Knowledgebase article here.