PoE Budget Planning for Cameras, Access Points and Phones

Two limits, and only one of them is on the label#

Every PoE switch has two power limits, and the one that causes trouble is the one nobody reads.

The first is per port, set by the PoE type the port supports: up to 15.4 W at the port for 802.3af Type 1, 30 W for 802.3at Type 2, 60 W for 802.3bt Type 3 and 90 W for 802.3bt Type 4.

The second is the switch’s total PoE budget: the wattage the internal supply can deliver across every port at once. That is the limit that actually runs out. A 48 port switch that supports 30 W on any port might carry a total budget of 740 W, while 48 ports at 30 W would be 1,440 W. The switch is fully capable on any port you pick and about half capable across the chassis, and both statements are true.

When the total is exceeded, a well behaved switch does not fail loudly. It denies power to the next device that asks, or sheds the lowest priority port. No alarm reaches anyone, and the fault gets diagnosed as a network problem three weeks later.

Sizing the budget is an estimating exercise, not a product selection exercise. Count the devices at the right number, add margin, and pick the switch from the total.

The four PoE types and what each delivers#

Type	Standard	Classes	Max at the port	Guaranteed at the device	Pairs	Typical loads	Cabling
Type 1	802.3af	0 to 3	15.4 W	About 13 W	2	Phones, fixed cameras, reader interfaces, clocks	Cat6 acceptable
Type 2	802.3at	4	30 W	25.5 W	2	Wi-Fi 6 access points, PTZ cameras, intercom panels	Cat6 or Cat6A
Type 3	802.3bt	5 and 6	45 W and 60 W	40 W and 51 W	4	Wi-Fi 6E and 7 access points, PTZ with heater, multi sensor cameras	Cat6A
Type 4	802.3bt	7 and 8	75 W and 90 W	62 W and 71.3 W	4	Displays, PoE lighting, high power access points	Cat6A

The gap between the port figure and the device figure is not a rounding error. It is the standard’s allowance for what the cable dissipates over a worst case 100 m channel, a 90 m permanent link plus 10 m of patch cords. A device rated to draw 51 W needs a 60 W port because roughly 9 W is budgeted to be lost in the cable on the longest permitted run. On a short run less is lost, but the switch still allocates against the class.

The pairs column surprises people upgrading old plant. Class 5 and above require power on all four pairs, so a cable with a damaged or unused pair that has carried a Type 1 phone for a decade will not carry a Type 3 access point. The failure looks like a device that boots and reboots rather than a cabling fault.

Conductor size matters at the top of the range. 23 AWG Cat6A has lower resistance than 24 AWG Cat6 and loses less over the run, and small gauge patch cords such as 28 AWG carry length restrictions in high power PoE channels.

Building the device count for one switch#

The count is per switch, not per building or per floor. Two switches in the same rack have two separate budgets, and stacking does not pool PoE budget across members on most platforms.

Everything that draws power over Ethernet goes on the list:

• Wireless access points, at the class the specific model requires, not what the generation implies
• Fixed cameras, and separately the pan tilt zoom cameras, which draw far more when the heater runs
• Desk and conference phones, including the ones not yet ordered
• Intercom and entry panels, and reader interface boards on the network
• Master clocks, bell devices, ceiling speakers, amplified paging endpoints, displays and signage players
• Access control door controllers and IO boards, occupancy sensors, building automation controllers

Count each device at the maximum its assigned class allows at the port. This is where most spreadsheets go wrong: a switch that allocates by class reserves the class maximum for that port whether the device uses it or not, so the reserved total is what fills the budget. Where the platform and the device negotiate a lower allocation over LLDP the reservation drops, but that is per platform and should not be assumed at design time.

The high draw devices decide the estimate. A PTZ with a heater and a blower pulls its maximum on the coldest night of the year. A multi sensor camera with four imagers is not a 15 W device, and a Wi-Fi 7 access point with three radios and a 10 Gb/s uplink is not a 30 W device.

A worked PoE budget for a floor IDF#

Assumptions, stated so they can be changed: one IDF serving one office floor, one 48 port switch, every device counted at the maximum its assigned class allows at the port, no diversity factor, growth margin of 25 percent, one spare port at day one. Every figure in the power columns is power sourcing equipment output at the switch port, which is the end a switch budget is spent from. The lower figure guaranteed at the device is what a data sheet quotes, and the two must not be mixed in one column.

Device on this switch	Count	Class assumed	PSE port output each, W	PSE port output total, W
Wi-Fi 7 access point	6	Class 6, Type 3	60.0	360.0
Fixed dome camera	14	Class 3, Type 1	15.4	215.6
PTZ camera with heater	2	Class 6, Type 3	60.0	120.0
Desk phone	18	Class 2, Type 1	7.0	126.0
Door controller and reader interface	3	Class 3, Type 1	15.4	46.2
Ceiling speaker amplifier and clock	4	Class 2, Type 1	7.0	28.0
Day one total	47 ports			895.8
Growth margin at 25 percent				224.0
PoE budget to specify				1,119.8

A 48 port switch with a 740 W budget does not carry this floor on day one, let alone after growth, and it is a common switch to find in the rack. The options are a larger internal supply, a second switch splitting the load, or an external power shelf where the platform supports one. All three are cheaper decided now than discovered after turnover.

Notice where the power sits. Six access points and two PTZ cameras are eight ports out of forty seven and 480 W out of 896 W: fifty four percent of the power on seventeen percent of the ports. That is the shape of almost every modern IDF, and it is why estimating access points loosely produces a budget that is wrong in the direction that matters.

A switch sized exactly to 896 W is full the first time someone adds a camera at a new door, an access point in a dead conference room, or an intercom panel at a side entrance, and all of those land in the higher classes. Our network room buildout page and our MDF and IDF buildout guide cover the room that has to hold the second switch.

Heat in bundles, cable loss and TIA TSB-184-A#

Power over Ethernet raises conductor temperature, and a bundle does not shed that heat evenly. Current flows on all four pairs at Type 3 and Type 4, and the cables at the center of a bundle cannot dissipate to open air. Insertion loss rises with temperature. A link that certified with margin on an empty floor in February can drift toward the limit years later, once the access points, cameras and PoE displays all draw at once above a warm ceiling in August. It presents as intermittent errors on specific ports and nobody connects it to the power.

TIA TSB-184-A gives guidance on bundle size, temperature rise and cable selection for power delivery over balanced twisted pair. For a design that means:

• Larger conductors dissipate heat better. 23 AWG Cat6A runs cooler than 24 AWG Cat6 at the same current, a second reason to run Cat6A to high power drops on top of the bandwidth reason in our Cat6 vs Cat6A guide.
• Smaller bundles run cooler. Break a 96 cable J-hook run into several bundles rather than one dense one.
• Do not pack cable tightly into sealed pathways. Conduit and sealed raceway are the worst case; open tray and J-hooks with air around the bundle run cooler.
• Elevated ambient temperature eats the margin first. A plenum above a warehouse roof is not a 20 degree Celsius space.

Code sets a floor under this. The California Electrical Code limits the current a bundle may carry, by conductor size and by the number of cables bundled together, and it recognizes cable listed as LP, limited power, which carries its own current rating printed on the jacket. Confirm the article and section numbers against the edition the project is permitted under, because the power-limited cable articles were reorganized in the 2023 NEC the 2025 CEC is based on. On a floor with PoE lighting, high power access points and PTZ cameras, naming a maximum bundle size in the specification gets the limit priced rather than discovered.

UPS sizing and what should stay up in an outage#

Sizing the UPS starts with the number you just calculated, because the PoE load is most of what the switch draws from the wall. Size for the actual load, meaning the calculated PoE draw plus the switch’s own consumption and conversion losses, not the nameplate. Then choose runtime deliberately. Fifteen minutes covers a utility blip; riding out a real outage or bridging to a generator start is a different specification.

Then decide what has to stay up, a policy question the owner answers and the design implements:

• Phones, where the building relies on them for emergency calling
• Cameras and whatever records them, because powering cameras while the recorder is dark produces nothing
• The access control head end and the door controllers, so credentials keep working and events keep logging
• The switching and wireless that staff need to work the incident

If the building has a generator, the IDF circuits should be on it, and that is an electrical design decision made early rather than a change order later. Batteries are consumables, so the replacement interval belongs in the maintenance plan. The dedicated circuits, the receptacles at the racks and the UPS connection are electrical, C-10 scope. Telelink Business Services is a licensed C-7 Low Voltage Systems Contractor, CSLB License #472017, and we show that handoff on our submittals.

What an undersized PoE budget looks like in the field#

It does not look like a power problem. That is the difficulty.

Access points drop radios or reduce transmit power when they cannot get a full allocation. The 6 GHz radio disables itself, coverage shrinks, and users report that the wireless is slow in the afternoon when the floor fills up. The access point is up, pingable, and green on the dashboard.

Cameras reboot. A PTZ that boots, runs its heater, browns out and boots again produces a loop that looks like a defective camera and gets replaced under warranty with an identical camera that does the same thing. It is worst on cold nights.

Ports get shed by priority, and the lowest priority device goes dark. If nobody set the priorities deliberately, that may be a door controller at a service entrance nobody checks. Phones drop mid call while an unrelated device is being installed on the same switch, because the new request pushed the chassis past its budget.

The diagnostic is straightforward once someone looks. Every managed PoE switch reports allocated and consumed power per port and for the chassis. Pull the peak over a week rather than the instantaneous reading, check the log for ports denied power, and compare against the published budget. If allocated power sits near the budget, the switch is already the constraint. Our wireless networks and Wi-Fi and security camera systems pages cover the two largest loads, and our Wi-Fi 6 versus 6E versus 7 guide covers what newer access points require at the port.

Next step#

Send the device schedule, the floor plans with the IDF locations, and the switch models you have or plan to buy through request a bid. We will return a powered device count per switch, the PoE budget each IDF needs with growth margin, the cabling category for those drops, and the UPS load. Where a general contractor carries Division 27, the electrical handoff for circuits and the UPS is marked on the submittals described on the for general contractors page.