Why PoE Budgeting Matters for Security Systems

The most common cause of “cameras going offline” we see in system takeovers isn’t bad cameras or faulty wiring — it’s PoE budget exhaustion. The switch runs out of power and starts dropping devices. Here’s why this happens and how to prevent it.

What Is PoE Budget?

Power over Ethernet (PoE) delivers electrical power alongside data over standard Ethernet cables. A PoE switch has a total power budget — the maximum watts it can deliver across all ports simultaneously. For example, a UniFi USW-Pro-24-PoE provides 400W across 24 ports.

Each connected device draws some of that budget:

• A typical IP camera: 12-25W (depending on model and features)
• A PTZ camera: 30-60W
• A PoE access point: 15-25W
• A card reader/controller: 10-15W
• An IP intercom panel: 15-25W

The Math Problem

Here’s where it goes wrong. Someone installs a 24-port switch with a 190W PoE budget and connects 16 cameras. They see that each camera’s spec sheet says “max 15W” and calculate: 16 × 15W = 240W. Already over budget, but the installer either doesn’t check or assumes cameras won’t draw max power simultaneously.

In reality, cameras draw peak power when IR illumination activates at night, when heaters engage in cold weather, or when motors adjust for zoom. On a cold Chicago winter night, every outdoor camera might hit its peak draw at the same time. The switch can’t supply enough power and starts cycling ports — cameras drop offline in rotation.

How to Budget Correctly

1. Use Actual Peak Draw, Not Average

Don’t use the “typical” power consumption from spec sheets. Use the maximum rated draw for every device. That’s the number that matters when all devices peak simultaneously.

2. Add 20-30% Headroom

After calculating total peak draw, add headroom. This accounts for future devices, environmental variables, and power delivery losses over longer cable runs.

3. Account for Cable Length

PoE loses efficiency over distance. A 100-meter cable run delivers less usable power at the device than a 10-meter run. For warehouses and large facilities with long runs, this matters.

4. Choose the Right PoE Standard

• PoE (802.3af): 15.4W per port — sufficient for basic cameras and access points
• PoE+ (802.3at): 30W per port — needed for PTZ cameras, powerful APs, and intercom panels
• PoE++ (802.3bt): 60-90W per port — for high-power devices

Make sure your switch supports the standard your devices need.

A Real-World Example

A 12-camera system with 4 outdoor cameras (25W max each) and 8 indoor cameras (15W max each):

• Outdoor cameras: 4 × 25W = 100W
• Indoor cameras: 8 × 15W = 120W
• Total peak draw: 220W
• With 25% headroom: 275W minimum switch budget

A switch with 190W PoE budget? Not enough. A switch with 400W? Comfortable, with room to grow.

Read our PoE switching and network design page for more detail, or check our PoE switch selection guide.

Contact us if you need help designing a properly powered security network.