What's the difference between 802.3af, 802.3at and 802.3bt?

802.3af (PoE) delivers up to 15.4W per port, 802.3at (PoE+) up to 30W, and 802.3bt (PoE++) up to 60W (Type 3) or 90W (Type 4). PTZ cameras with heaters and multi-radio access points typically need PoE+ or PoE++.

Why leave 20% headroom on a PoE switch?

Device draw spikes at boot, when IR illuminators switch on at night, and when PTZ motors or heaters run. Loading a switch past about 80% of its budget risks ports browning out exactly when cameras need power most — cold nights.

PoE Power Budget Calculator

Q: What is a PoE power budget?

A PoE switch has a total wattage it can deliver across all ports — its power budget. A 24-port switch might supply 30W per port individually but only 190W total, so it cannot power 24 high-draw devices at once.

Add every powered device on the switch, set your switch's total PoE budget, and see whether the design fits — including the 80% headroom rule that keeps IR cameras alive on cold nights.

Devices on this switch

Device type	Qty	W each

Switch PoE budget (W)

On the switch datasheet: “PoE power budget”. Common: 65 / 130 / 190 / 370 / 740 W.

PoE ports on switch

Power budget check

—

total device draw → —

Switch budget—

Budget used—

Recommended max load (80%)—

Headroom remaining—

Ports used / available—

Minimum PoE standard needed—

Design to ≤80% of the switch budget. IR illuminators, heaters and PTZ motors spike draw beyond the idle rating.

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Typical PoE device power draw

Device	Typical draw	Standard needed
Fixed IP camera (no IR)	4–6 W	802.3af
Fixed IP camera with IR	7–13 W	802.3af
PTZ camera	15–25 W	802.3at (PoE+)
PTZ with heater/blower	30–60 W	802.3bt (PoE++)
Wi-Fi access point	10–20 W	802.3at
VoIP desk phone	3–7 W	802.3af
Access control door controller	8–13 W	802.3af/at
Intercom / video doorbell station	8–15 W	802.3af/at

The mistake that takes systems down in winter

A camera that idles at 6 W can pull 12 W the moment its IR array switches on at dusk — and every camera on the switch does it at the same time. Add a cold-weather heater cycle and a switch that looked fine on paper starts dropping ports in January. That's why professional designs keep total connected load at or below 80% of the switch's PoE budget, and why per-port limits matter as much as the total.

Frequently asked questions

What is a PoE power budget?

The total wattage a switch can deliver across all ports at once. A 24-port PoE+ switch can do 30 W on any single port, but its 190 W total budget means it can't do 30 W on all 24 simultaneously.

802.3af vs at vs bt?

af (PoE) = up to 15.4 W per port, at (PoE+) = 30 W, bt (PoE++) = 60–90 W. PTZs with heaters and multi-radio access points typically need at or bt.

Why leave 20% headroom?

Draw spikes at boot, at dusk when IR turns on, and when motors/heaters run. Past ~80% load you risk brownouts exactly when the cameras matter most.

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