A PoE switch can power all of your cameras only if its total power budget exceeds the real-world draw of every connected device — not the spec-sheet draw, but the draw after you account for cable losses, cold-weather heaters, infrared illuminators, and a safety margin. The short formula is: add up the worst-case wattage of each camera, multiply by roughly 1.15 to cover cable loss, then add 20–25% headroom for growth and peak load. If the switch's published PoE budget clears that number, you are sized correctly. The rest of this guide walks an integrator or facilities buyer through the calculation step by step so your camera system comes up on day one and stays up under load.
Getting the PoE budget for cameras right is one of those quiet decisions that either disappears into the background or causes months of intermittent reboots. It is worth doing carefully.
Step 1: Inventory every camera and its true peak draw
Start with a line-item list of every device that will pull power from the switch. For each camera, find the maximum power consumption, not the typical figure. Datasheets usually list both, and the gap is large.
A fixed dome in good light might idle at 4–5 W but climb to 12 W once the infrared LEDs switch on at night. A pan-tilt-zoom (PTZ) camera with a motor and a heater can spike well past 25 W during a cold-weather move. Bullet cameras with long-range IR sit somewhere in between.
Group your devices by their PoE class so the math stays honest:
- PoE (802.3af), Class 0–3: up to 15.4 W delivered at the switch port
- PoE+ (802.3at), Class 4: up to 30 W at the port
- PoE++ / 4PPoE (802.3bt), Type 3/4: up to 60 W or 90 W at the port
Always budget at the port delivery figure, because that is what the switch must actually source. A camera rated for "12.95 W at the device" still obligates the switch to provide more than that.
Step 2: Account for cable loss before you trust the number
This is the step most spreadsheets skip, and it is the one that causes brownouts on long runs. Power injected at the switch port travels through copper that has resistance, so a measurable fraction of it turns into heat before it reaches the camera. The longer and thinner the cable, the bigger the loss.
The PoE standards are written to tolerate this — the device-side rating is already lower than the port-side rating for exactly this reason. But when you are sizing the switch budget, you must reserve the port-side wattage, including the loss. A practical rule of thumb: add about 15% on top of device draw to cover cabling losses on runs approaching the 100-meter limit. Shorter runs lose less; if most of your cameras are within 30–40 meters, you can trust the class budget without much padding.
Pitfall to flag now: cheap copper-clad-aluminum (CCA) cable has far higher resistance than solid copper and will not deliver rated PoE over distance. For any federal or enterprise install, specify solid-copper, properly rated cable. It is also a supply-chain and warranty matter, not just an electrical one.
Step 3: Add environmental and feature loads
Cameras do not live in a datasheet. Real deployments add power-hungry features that only appear under certain conditions:
- Heaters and blowers in outdoor housings can double a camera's draw on a freezing morning — exactly when you least want a brownout.
- Infrared illuminators turn on every night, so for any 24/7 site the "night" number is your real number.
- Audio, edge analytics, and onboard storage each add a watt or two.
- PTZ motion draws transient peaks that exceed the steady-state figure.
If any of these apply, use the highest combined value the camera can hit at once. Your switch has to survive the coldest, darkest, busiest moment — not the average Tuesday afternoon.
Step 4: Total the load and compare to the switch budget
Now sum the adjusted, worst-case wattage across all cameras. Compare that total to two numbers on the switch datasheet, because they are different:
- Total PoE power budget — the watts the switch can deliver across all ports combined. This is usually limited by the internal or external power supply, and it is often less than the sum of all ports running at max.
- Per-port maximum — the most any single port can source. A PTZ on PoE++ needs a port that supports 60–90 W even if the overall budget is fine.
A 24-port switch advertised as "PoE+" rarely means 24 × 30 W. Read the aggregate budget. Many mid-range switches deliver 370 W or so across all ports — plenty for two dozen efficient domes, not enough for two dozen heated PTZs.
Step 5: Build in headroom and redundancy
Never spec a switch to run at 100% of its budget. Targets we recommend:
- Plan to load no more than 75–80% of the aggregate budget. The remaining 20–25% absorbs peak transients, future cameras, and the slow power creep of firmware updates that enable more features.
- Match the switch to your uptime needs. For critical surveillance, choose a switch with dual or redundant power supplies, and put the whole closet on a properly sized UPS — the cameras are only as available as the switch and the power behind it.
- Leave physical ports free, too. A switch that is full on day one forces a forklift upgrade the first time someone adds a door or a gate camera.
Worked example: ten outdoor IR bullets at a worst-case 12 W, plus four heated PTZs at 50 W each. Device load is (10 × 12) + (4 × 50) = 320 W. Add 15% for cable loss → about 368 W. To stay under 80% loading, you want a switch budget of roughly 368 ÷ 0.8 ≈ 460 W, with PoE++ ports for the PTZs. A 370 W switch would technically "fit" the raw load and then fail the first cold night.
Compliance and lifecycle: the part buyers forget
The electrical math is only half the decision. The switch carrying your camera network is itself networked infrastructure, which means it falls squarely inside your NDAA Section 889 and TAA obligations. A non-compliant switch quietly powering compliant cameras still puts a federal contract at risk, and it is the kind of detail that surfaces during an audit rather than at purchase.
As a vendor-neutral integrator, we size the PoE budget for cameras independently of any single manufacturer, then select compliant switches that meet the wattage, port-count, and redundancy targets — and we document the calculation so it survives staff turnover and renewal cycles. Sizing for today's camera count alone is the most common and most expensive mistake; we plan the closet for the system you will have in three years, not just the one you are installing this quarter.
Get the calculation done right the first time
If you would rather hand off the worst-case wattage math, the compliance check, and the redundancy planning to a team that does it daily, request a quote and we'll size your PoE infrastructure end to end.