PoE Budget for IP Cameras: How to Plan

A PoE switch that looks big enough on paper can still drop cameras at 2 a.m., when every infrared illuminator switches on at once. Planning the PoE budget for IP cameras means knowing what each camera draws at its worst, what each switch port can deliver, and how the switch counts power against its total. This guide walks through the standards, the math and the field details that decide whether a system stays up.

What a PoE budget is

A PoE switch has two separate limits. Each port has a maximum it can source, set by the PoE standard it supports. The switch also has a total power budget shared by all ports, and on most switches that total is well below the per port maximum multiplied by the port count.

The standards call the switch or injector the PSE (power sourcing equipment) and the camera the PD (powered device). Both numbers matter: the PSE figure is what the switch must reserve, and the PD figure is what reaches the camera after the cable takes its share.

802.3af vs 802.3at vs 802.3bt power levels

The Ethernet Alliance overview of the 802.3bt PoE standard lists the power at the switch port and at the device for each type. The figures below are the top class of each type.

Types 1 and 2 deliver power over two pairs. The same overview notes that for Class 5 and higher, power delivery requires all four pairs, so cameras above Class 4 need all eight conductors terminated. In the 802.3af vs 802.3at decision, most fixed cameras fit 802.3af, while PTZ cameras and cameras with heaters usually need 802.3at or more.

Why the switch side and the camera side differ

Cable resistance turns some power into heat before it reaches the camera. The standard specifies correct operation for a pairset DC loop resistance of up to 12.5 ohms, which is why a Class 4 port sources 30 W but promises the device only 25.5 W.

Budget on the switch side. If a switch reserves power by class, a Class 3 camera takes 15.4 W from the budget no matter what the camera actually uses.

What IP cameras really draw

Use the maximum power figure on the camera datasheet, not the typical figure. Draw climbs at night when IR illuminators come on, in winter when housing heaters run, and whenever a PTZ motor moves. Installer forums are full of threads about cameras that reboot only after dark, and the cause is usually a switch that ran out of power once every camera switched to IR.

How the switch allocates power matters as much as the cameras. Some switches reserve the full class maximum per port, while others allocate by measured draw or by what the camera requests over LLDP. The Ethernet Alliance notes that all PDs above Class 3 must support this LLDP classification. 802.3bt adds Autoclass, which lets the switch measure real draw and “power more ports from a limited power supply budget.”

How to calculate a PoE switch power budget

1. List every powered device on the switch: cameras, access points, door controllers.
2. Write down each camera’s maximum draw and its PoE class from the datasheet.
3. Total the maximum draws, then add about 20 percent headroom for aging, cold starts and added cameras.
4. Total the class reservations as well, in case the switch allocates by class.
5. Pick a switch whose budget covers the larger total, with ports of the right type for every camera.

Here is a worked example with illustrative figures, not any specific model. A site has eight fixed domes at 6 W maximum, four IR bullets at 11 W and one PTZ at 25 W. Measured draw is 48 + 44 + 25 = 117 W, or about 140 W with headroom.

Allocated by class, the same cameras reserve far more. Eight domes and four bullets sit in Class 3 at 15.4 W each, and the PTZ needs Class 4 at 30 W. That is 123.2 + 61.6 + 30 = 214.8 W, so a 150 W switch passes the first test and fails the second.

Cable, distance and heat

PoE runs follow the same 100 meter channel as Ethernet data. Long runs, thin conductors and poor terminations all raise loop resistance, which costs power and can push a camera below its operating voltage. Use solid copper Category cable and skip copper clad aluminum, which has higher resistance.

Heat builds up in large bundles carrying PoE, which matters more at 802.3bt levels. The Ethernet Alliance’s PoE cabling guidance recommends keeping bundles to a maximum of 24 cables. Our CMR vs CMP cable guide covers jacket ratings for those runs.

Choosing the switch

Match the port types to the camera list first, then the total budget. A switch with mostly 802.3at ports and a few 802.3bt ports handles a typical mixed site, and an injector can feed a single high power camera without upsizing the whole switch.

• Leave spare ports and spare budget for the next camera.
• Prefer managed switches that show per port wattage, so night load can be checked after install.
• Size the UPS to the PoE load plus the switch itself, because the cameras go down when the switch does.
• Outdoors or in a remote closet, house the switch in a weather rated network enclosure.

Where to buy PoE switches and cameras

Bursma Distributing, established in 1947, sells only to dealers, installers and integrators. PoE switches are in the network switches category of the Broadband and WiFi division. Cameras are in security cameras, recorders in video recorders, and Category cable in bulk wire. If the recorder choice is still open, read DVR vs NVR: choosing a recorder.

Dealers see their own pricing and stock in Shop Online after logging in. Open a dealer account, or call the Wyoming, Michigan branch at 616-831-0080 or the Columbus, Ohio branch at 614-299-9040.

Frequently asked questions