Sizing PoE for IP Cameras: A Real-World Example

IP cameras are common PoE devices, but their power requirements vary dramatically. A basic fixed camera might need 7W while a PTZ with heater could demand 60W. Here's how to size your PoE budget correctly.

PoE Budget Calculator Calculate total PoE power requirements for your cameras

The Scenario

You're deploying a camera system with:

• 10 indoor fixed dome cameras
• 6 outdoor bullet cameras (need heaters)
• 2 outdoor PTZ cameras (pan-tilt-zoom with heaters)
• 2 entrance cameras with built-in speaker/microphone

All cameras connect to a single IDF (intermediate distribution frame) within 100 meters.

Step 1: Find Maximum Power Draw

Check the datasheet for each camera model. Look for "maximum power consumption," not typical or average:

Camera Type	Typical	Maximum	PoE Class
Indoor fixed dome	7W	12W	Class 3 (802.3af)
Outdoor bullet with heater	12W	25W	Class 4 (802.3at)
Outdoor PTZ with heater	30W	60W	Class 6 (802.3bt Type 3)
Entrance camera with audio	10W	15W	Class 4 (802.3at)

Why maximum matters: Heaters activate during cold weather. IR illuminators turn on at night. PTZ motors draw peak power during movement. Your switch must handle all these simultaneously.

Step 2: Calculate Total Load

Camera Type	Count	Max Each	Total
Indoor fixed dome	10	12W	120W
Outdoor bullet with heater	6	25W	150W
Outdoor PTZ with heater	2	60W	120W
Entrance camera with audio	2	15W	30W
Total Maximum Load	20	-	420W

Step 3: Add Safety Margin

Add 20% headroom for:

• Future camera additions
• Cable loss over long runs
• Power supply degradation over time
• Inrush current during boot sequences

420W × 1.20 = 504W required PoE budget

You need a switch (or switches) with at least 504W total PoE budget.

Step 4: Verify Per-Port Power

Total budget isn't enough—verify per-port maximums match camera needs:

Camera Needs	Required	Switch Must Support
Indoor fixed (12W)	802.3af (12.95W)	All ports
Outdoor bullet (25W)	802.3at (25.5W)	At least 6 ports
PTZ with heater (60W)	802.3bt Type 3 (51W)	At least 2 ports*
Entrance camera (15W)	802.3at (25.5W)	At least 2 ports

*Note: The PTZ needs 60W but 802.3bt Type 3 delivers only 51W at the device. You may need Type 4 or a midspan injector. Always verify camera will work with available power.

Step 5: Select Appropriate Switch

Options for 504W budget with 802.3bt support:

Option	Ports	PoE Budget	Notes
24-port PoE++ switch	24	720-800W typical	Best option, room to grow
48-port PoE+ switch	48	740W typical	May not support 60W per port
Two 12-port PoE++ switches	24	500W total	More complex management

A 24-port 802.3bt switch with 720W budget handles this deployment with room for 4 more cameras.

Common Gotchas

1. Not All Ports Are Equal

Some switches have limited high-power ports:

• "8 ports 802.3bt, remaining ports 802.3at"
• "4 ports can deliver 60W, others limited to 30W"

Read the datasheet carefully. Don't assume all ports match the highest specification.

2. Total Budget Limits

A switch advertised as "24-port PoE+ with 370W" can't deliver 30W to all 24 ports (that would be 720W). It can deliver:

• 12 ports at 30W each (360W), or
• 24 ports at 15W each (360W), or
• Some mix within 370W total

3. Temperature Effects

Outdoor cameras with heaters may draw maximum power on the coldest days—exactly when you don't want cameras to fail. Assume worst-case weather when calculating.

4. Startup Inrush

Cameras draw extra power during boot. If all cameras restart simultaneously (after a power event), momentary load can exceed steady-state calculations. Quality switches handle this; cheap ones may not.

The 60W PTZ Problem

Many enterprise PTZ cameras with heaters need more than 802.3at's 25.5W but may not quite fit 802.3bt Type 3's 51W delivery. Options:

• 802.3bt Type 4: Delivers up to 71W at the device
• Midspan injector: Dedicated high-power injector for these ports
• Local power: Run AC power to an outdoor enclosure
• Different camera: Some PTZ cameras are designed for lower power

Summary: Your Camera PoE Checklist

1. Find maximum power draw for each camera model (from datasheet)
2. Sum all maximum draws
3. Add 20% safety margin
4. Verify per-port power matches camera requirements
5. Select switch with sufficient total budget AND per-port capability
6. Consider midspan injectors for high-power outliers
7. Document everything for future reference