PoE Budget Explained: How Many APs and Cameras Can a Switch Power?

A switch can power as many devices as its total PoE budget allows, and no port can deliver more than its PoE standard allows. Those are two separate limits, and most PoE problems come from checking only one of them. A switch with 48 PoE+ ports can light 48 links; whether it can power 48 access points at full PoE+ draw depends on the budget, which is often well below 48 times the per-port maximum. To size a switch properly, add up what each access point, camera and phone will draw (or what the switch will reserve for it), add headroom, and compare that to the budget of the switch with the power supplies you are actually buying.

PoE vs PoE+ vs PoE++: what is the difference?

They are successive IEEE standards, each delivering more power per port. The switch-side figure is what the port supplies; the device-side figure is what remains after losses on up to 100m of cable:

• PoE, IEEE 802.3af (Type 1): up to 15.4W per port at the switch, 12.95W at the device.
• PoE+, IEEE 802.3at (Type 2): up to 30W at the switch, 25.5W at the device.
• PoE++, IEEE 802.3bt Type 3: up to 60W at the switch, 51W at the device, delivered over all four pairs.
• PoE++, IEEE 802.3bt Type 4: up to 90W at the switch, 71.3W at the device.

The standards are backward compatible. An 802.3af camera works on a PoE+ port, and a PoE+ access point works on an 802.3bt port. The reverse is where trouble starts: a device that needs more than the port can supply either fails to power on or, as many access points do, runs with features such as radios or ports disabled.

What are PoE power classes?

During detection, a powered device advertises a class, which tells the switch the most it may draw. The switch-side allocation for each class is fixed by the standard: class 1 is 4W, class 2 is 7W, class 3 is 15.4W, class 4 is 30W, class 5 is 45W, class 6 is 60W, class 7 is 75W and class 8 is 90W. Class 0 (unclassified) is treated as 15.4W. Classes 0 to 3 are 802.3af, class 4 is 802.3at, and classes 5 to 8 need 802.3bt. The class is on the device datasheet, usually next to its maximum power consumption.

How do I calculate a PoE budget?

• List every powered device: access points, cameras, phones, badge readers, displays. Record each one's class and maximum draw from its datasheet, not its typical draw.
• Find out how the switch allocates power. Class-based allocation reserves the full class figure (30W for a class 4 access point, even if it draws less). Allocation by actual consumption or LLDP negotiation reserves closer to real draw. Many switches let you choose.
• Sum the reservations under the allocation mode you will use.
• Add 20 to 30% headroom for growth, device swaps and firmware changes that raise power draw.
• Compare the total with the switch's PoE budget for the power supply configuration you are buying, in the redundancy mode you will run.

A worked example with class-based allocation: 12 Wi-Fi access points at class 4 reserve 12 x 30W = 360W, and 20 fixed cameras at class 3 reserve 20 x 15.4W = 308W, for 668W in total. With 25% headroom you need about 835W of available PoE. A 48-port PoE+ switch with a smaller budget would bring up every link but not power every device. The same devices under allocation by actual draw may need considerably less, which is why the allocation mode matters as much as the budget figure.

How many PoE devices can my switch power?

Divide the available budget by the per-device reservation, then cap the answer at the number of PoE ports. Every 300W of budget powers ten class 4 devices reserved at 30W, or 19 class 3 devices reserved at 15.4W. The budget itself varies by model and often by power supply option, so take it from the product page of the exact configuration, not from the family datasheet. The 48-port PoE+ access switches Nexus Compute supplies include:

• Cisco Catalyst C9300-48P: 48x 1GbE PoE+, modular uplinks (1/10/25/40G), stackable, IOS XE and DNA Center.
• Juniper EX4400-48P: 48x 1GbE PoE+, 10/25GbE SFP28 or 100GbE QSFP28 uplink module, stackable, Junos with Mist AI cloud management.
• HPE Aruba CX 6300M JL665A: 48x 1GbE PoE+, 4x 50GbE SFP56 uplinks, stackable, AOS-CX and Aruba Central.
• Fortinet FortiSwitch FS-448E-POE: 48x 1GbE PoE+, 4x 10GbE SFP+ uplinks, managed from a FortiGate via FortiLink.
• Also available: the Juniper EX2300-48P, HPE Aruba 2930F JL256A and Dell EMC PowerSwitch N3248P-ON, all with 48x 1GbE PoE+.

For smaller closets, 24-port options include the Cisco Catalyst C9200L-24P-4G (24x 1GbE PoE+ plus 4x 1G SFP, stackable) and the NETGEAR M4250-26G4F-PoE+ (24x 1GbE PoE+ plus 4x 1G SFP), a common choice for AV-over-IP. Where Wi-Fi 6E or Wi-Fi 7 access points need faster ports, the UniFi USW-Enterprise-24-PoE provides 24x 2.5GbE PoE+.

Port count tells you how many devices you can connect. PoE budget tells you how many you can power. Size on the second.

How much power do access points and cameras need?

Always use the datasheet, but the patterns are consistent. Many recent tri-radio Wi-Fi 6E and Wi-Fi 7 access points specify 802.3at for full functionality, and some specify 802.3bt; on a lower-power port they may run with a radio or a port disabled. Fixed dome and bullet cameras commonly sit in the lower classes. PTZ cameras, and outdoor cameras with heaters or IR illuminators, can need PoE+ or 802.3bt. IP phones typically sit in the lowest classes. Every switch listed above provides PoE+ on its RJ45 ports, so class 5 to 8 devices need an 802.3bt-capable model from the Cisco enterprise switching or Ubiquiti UniFi ranges. Our Wi-Fi 7 campus guide covers access point planning beyond power.

What else limits PoE besides the budget?

• Power supply configuration: on switches with modular or dual power supplies, the PoE budget depends on which supplies are fitted and whether they run in redundant or combined mode. Redundant mode usually leaves less power for PoE.
• Port priority: when demand exceeds the budget, the switch refuses power to new devices or sheds lower-priority ports. Set priorities so access points and security cameras outrank non-critical devices.
• Cabling: 802.3bt Types 3 and 4 use all four pairs, so every pair must be terminated. Large bundles of high-power PoE cable run warmer, so follow your cabling standard's bundle guidance.
• Reloads: check whether the switch can keep PoE up through a software reload, or cameras and access points will drop during every upgrade.

Nexus Compute supplies new PoE access switches from Cisco, Juniper, HPE Aruba, Fortinet, Dell, NETGEAR and Ubiquiti through authorized distribution. Send your device list with classes or maximum draw via request a quote, and we will check it against the PoE budget of the quoted configuration and return pricing within 48 business hours.