Power over Ethernet (PoE) is the backbone of modern IP surveillance. It carries both data and electrical power over a single Ethernet cable, so each camera needs only one run of Cat5e or Cat6 rather than a separate power outlet at every mounting point. That simplicity is exactly why PoE is easy to get wrong: buy a switch or recorder without enough power headroom, and cameras reboot randomly, drop offline at night when infrared illuminators kick in, or refuse to power up at all. This guide explains the PoE standards, what each one actually delivers, and how to size a power budget that keeps every camera stable.
The three PoE standards you need to know
PoE is defined by IEEE 802.3 standards. Each newer revision raises the maximum power a port can supply. Because some power is always lost as heat over the cable, there is a difference between the wattage a switch delivers at the port (PSE) and the wattage the camera actually receives (PD). Both numbers matter when you plan a system.
| Standard | Common name | Power at port (PSE) | Power at device (PD) | Typical use |
|---|---|---|---|---|
| 802.3af | PoE | 15.4 W | 12.95 W | Fixed dome/bullet cameras |
| 802.3at | PoE+ | 30 W | 25.5 W | PTZ, IR, heated housings |
| 802.3bt Type 3 | PoE++ | 60 W | 51 W | High-power PTZ, multi-sensor |
| 802.3bt Type 4 | PoE++ | 100 W | 71.3 W | Heaters, edge compute, displays |
A word of caution about passive PoE and proprietary schemes: some budget cameras and injectors use non-standard voltages (24 V passive PoE is common). Mixing passive PoE gear with standards-based 802.3af/at equipment can damage hardware because there is no negotiation handshake to confirm the device wants power. Whenever possible, stay within the IEEE standards so that the power sourcing equipment and the powered device negotiate safely before any voltage is applied.
Matching a camera to the right standard
Start with the camera datasheet, which lists a maximum power draw. A basic fixed 2 MP or 4 MP dome typically draws 4 to 7 watts and runs comfortably on plain 802.3af PoE. Add infrared night vision, a built-in heater, or a motorized varifocal lens and consumption climbs toward the 12 to 15 watt range, which is where PoE+ becomes the safer choice. Pan-tilt-zoom (PTZ) cameras are the biggest consumers: the motors, long-range IR, and sometimes a wiper or heater can push draw to 25 to 60 watts, requiring PoE+ or PoE++.
The key mistake buyers make is planning to the average draw instead of the peak. A camera might idle at 5 watts in daylight but spike well above that the moment IR LEDs activate at dusk or a PTZ slews to a preset. Size every port to the datasheet maximum, not the typical figure, or you will chase intermittent failures that only appear after dark.
Cable distance and quality still matter
PoE is rated for a 100-meter (328-foot) channel, and that limit covers both data and power. Beyond roughly 100 meters, voltage drop can starve a camera even if the switch has plenty of capacity. Thin copper-clad-aluminum (CCA) cable makes this worse: it has higher resistance than solid copper, so it wastes more power as heat and reduces effective range. For any PoE run, use solid bare-copper Cat5e or Cat6 that meets the standard. If you must exceed 100 meters, a PoE extender or a fiber transceiver with a remote PoE switch is the correct fix rather than pushing copper past its rating. Reliable structured cabling and the right networking hardware pay for themselves in avoided troubleshooting; you can browse switches, transceivers and accessories in our networking collection.
How to calculate a PoE power budget
Every PoE switch and every PoE NVR has a total power budget, expressed in watts, that is shared across all its PoE ports. This is the single most important number on the spec sheet, and it is almost always lower than the sum of the per-port maximums. An 8-port switch that advertises 30 W per port does not necessarily deliver 240 W total; it may cap out at 130 W. If you connect eight PoE+ cameras that each want 25 watts, you need 200 watts and the switch will start shedding load.
To size correctly, follow three steps. First, add up the maximum rated draw of every camera you plan to connect. Second, add a headroom margin of 20 to 25 percent for cable loss, cold-weather heater cycles, and future cameras. Third, choose a switch or recorder whose total PoE budget comfortably exceeds that figure. For example, twelve cameras drawing 12 watts each total 144 watts; with 25 percent headroom you want at least 180 watts of PoE budget, so a switch rated around 180 to 250 watts is appropriate.
- Step 1: Sum the datasheet maximum wattage of all powered devices.
- Step 2: Multiply by 1.2 to 1.25 for headroom.
- Step 3: Select a switch/NVR whose total PoE budget exceeds that number, and confirm per-port support matches your highest-draw camera.
Switch versus PoE NVR: where should the power come from?
You have two common architectures. A dedicated PoE switch feeds cameras and connects to a separate recorder over the network; this scales well and keeps recording and power on independent devices. Alternatively, many NVRs include built-in PoE ports, which is tidy for small deployments but ties your port count and power budget to the recorder you chose. If you expect to add cameras later, a standalone switch gives more flexibility, while an all-in-one PoE NVR is convenient for a fixed 4, 8, or 16-camera site. Compare recorders in our NVRs and recorders collection, and pair them with cameras and housings from the surveillance collection.
A quick pre-purchase checklist
- Confirm each camera's PoE class (af, at, or bt) against the switch's per-port capability.
- Verify the switch or NVR total PoE budget covers all cameras plus 20 to 25 percent headroom.
- Use solid-copper Cat5e/Cat6 and keep runs within 100 meters.
- Avoid mixing passive PoE injectors with standards-based equipment.
- Leave spare ports and watts if you plan to expand.
The bottom line
PoE removes the hassle of local power, but only if the numbers add up. Match each camera to the correct standard by its peak draw, respect the 100-meter copper limit, and above all size the switch or NVR total power budget with real headroom rather than the optimistic per-port figure. Get those three things right and your cameras stay online through the coldest, darkest nights, which is exactly when a surveillance system needs to be at its most reliable.