Most PoE jobs that come back as warranty calls were doomed at the spec stage. The switch had enough total wattage on paper, but nobody added up what the cameras and APs actually pull at peak — IR illuminators kicking on at dusk, Wi-Fi 6E radios under load, PTZ motors moving, heaters firing in cold weather. The result is a network closet where ports randomly drop, cameras reboot in loops, and the customer thinks the cabling is bad. It is almost never the cabling. It is the budget.
Here is how to spec PoE the right way the first time, with the math working installers actually use on site.
The PoE standards in plain English
There are four PoE flavors you will run into in the field, and they are not interchangeable on the same switch port:
- PoE (802.3af): 15.4W at the port, 12.95W guaranteed at the device. Fine for VoIP phones, basic indoor cameras, and small APs.
- PoE+ (802.3at): 30W at the port, 25.5W at the device. The current workhorse for fixed-dome cameras and Wi-Fi 5/6 APs.
- PoE++ Type 3 (802.3bt): 60W at the port, 51W at the device. PTZ cameras with heaters, Wi-Fi 6E APs with USB pass-through, small displays.
- PoE++ Type 4 (802.3bt): 90W at the port, 71W at the device. Multi-radio APs, large PTZs, thin clients, some displays.
The wattage at the port is what the switch has to deliver. The wattage at the device is what is left after worst-case cable loss over 100 meters of Cat5e. That gap is where most under-budgeting happens.
Why nameplate wattage is a lie
A camera spec sheet that says "12W typical" is telling you the average draw under normal conditions. What you actually need to budget for is the peak draw when every load is on at once. For a typical bullet camera that means:
- Sensor and SoC running at 30 fps
- IR LEDs at full power (cold night, full range)
- Heater and defroster active (winter mornings)
- Codec running H.265 at maximum bitrate
That "12W typical" camera can pull 22W or more in the field. Multiply that across 24 cameras and you are 240W over your switch budget without realizing it.
The 80% rule that saves jobs
Never spec a switch to more than 80% of its total PoE budget. A 370W switch should be loaded to 296W of peak device draw, not nameplate. Two reasons:
- Headroom for simultaneous peaks. When all cameras and APs spike at once (dusk transition, weather event, firmware update), you need slack.
- Heat derating. Switches in hot IDFs throttle PoE output before they shut down. A switch in a 95°F closet may only deliver 85% of rated wattage.
If you are designing close to the limit, step up to a higher-budget switch or split the load across two switches. The cost difference between a 370W and a 740W switch is far less than a return trip to swap one out.
How to actually budget a job
Build a simple worksheet before you order the switch. For every endpoint, list:
- Device type and model
- PoE class (af / at / bt Type 3 / bt Type 4)
- Peak wattage from the manufacturer's spec sheet (not "typical")
- Cable run length (loss matters past 80m)
- Whether it has a heater or moving parts
Sum the peaks, add 20% buffer, and that is your minimum switch PoE budget. Then check that the per-port class is supported — a switch with a big total budget but only 802.3at per port will not run a 60W PTZ no matter how much headroom you have.
Cable choice changes the math
PoE loss scales with resistance, and resistance scales with conductor size and cable length. Cat5e at 24 AWG over 100m loses meaningfully more than Cat6 at 23 AWG over the same run. For PoE++ runs near the 100m limit, Cat6 or Cat6a is not optional — it is the difference between a device that boots and one that does not.
Bundling matters too. Twelve PoE++ cables in a tight bundle generate real heat, and the TIA standard derates ampacity in dense bundles. Keep PoE bundles loose, use ladder rack instead of conduit fill, and never pull PoE through a hot ceiling space without checking jacket temperature ratings.
If you need to brush up on cable selection for PoE applications, our guide on Cat5e vs Cat6 vs Cat6a walks through the conductor and shielding tradeoffs in detail.
Common failure patterns
Cameras rebooting at dusk. IR LEDs kick on, draw spikes past the port budget, switch cuts power, camera reboots, IR turns off, switch restores power. Loop continues until daylight. Fix: move to PoE+ on a switch with proper per-port budgeting.
APs dropping radios under load. Wi-Fi 6E AP under heavy client load pulls more than its 802.3at port can deliver. Some radios shut down to stay within budget. Fix: PoE++ Type 3 minimum for Wi-Fi 6E and tri-radio APs.
Random port shutdowns in cold weather. Heated cameras in unconditioned spaces draw extra wattage when temps drop. Switch hits its total budget and starts dropping the lowest-priority ports. Fix: budget for heaters in the worst case, not nameplate.
Tools that catch this before the truck rolls
A PoE tester at install confirms the device is actually getting the wattage it negotiated for, not just link. Cable certifiers with PoE load testing simulate real draw and measure voltage drop end-to-end. Both pay for themselves the first time they catch a marginal run before the customer does.
Browse our testing tools and PoE testers for what installers actually carry. For switch and PoE infrastructure, see our power and PDU collection.
The short version
Spec to peak draw, not nameplate. Stay under 80% of switch budget. Use Cat6 or better for PoE++ near 100m. Test at commissioning, not after the callback. Every PoE problem you prevent at the spec stage is a problem you do not have to drive back to fix.