PoE budget planning when cameras, access control, and Wi-Fi share one switch — the math that gets skipped.

Power over Ethernet is now the default delivery mechanism for almost every low-voltage device in a commercial building: IP cameras, access control readers, Wi-Fi access points, VoIP phones, and intercom panels. When these systems are co-installed on shared switch infrastructure — as they frequently are in small to mid-size commercial buildings — the PoE budget of the switch becomes a critical engineering parameter that determines whether every device powers up as designed.

PoE under-provisioning is one of the most consistently under-analyzed failure modes in commercial low-voltage installations. The problem is invisible at design, survives rough-in, and announces itself at commissioning when someone tries to power up a switch with 30 devices and discovers that 8 of them aren’t receiving power. The failure mode on shared switches — and the OT/IT architecture issues underneath it — are covered in the shared switch architecture post. This post focuses specifically on the PoE budget math.

PoE standards and what they actually deliver

The IEEE 802.3 PoE standards define maximum per-port power budgets at the power sourcing equipment (PSE — the switch). The actual power delivered to the powered device (PD) is less, due to cable resistance losses. The distinction matters for budgeting:

The switch’s total PoE budget — the aggregate watts available across all ports — is the number that determines whether all devices can be powered simultaneously at maximum draw. A 24-port PoE+ switch with a 370 W total PoE budget can support 24 devices drawing an average of 15.4 W each. It cannot support 24 devices each drawing 30 W (which would require 720 W). Most switch vendors publish both per-port standard and total PoE budget in the datasheet, but the total budget is frequently overlooked in the design phase.

Typical PoE draws by device class

Planning PoE budgets requires actual wattage from the device specifications — not the IEEE standard maximum. A camera rated for 802.3at does not draw 30 W; it draws whatever the manufacturer specifies. Use the manufacturer’s listed maximum power consumption for planning, not the port standard:

• Fixed IP cameras (indoor, non-PTZ): Most current models draw 7–12 W at maximum operating load.
• PTZ cameras: 15–30 W depending on zoom motor and heater configuration. Outdoor PTZ cameras with embedded heaters draw closer to 30 W in cold conditions.
• Access control readers (card-only, no door hardware): 3–8 W for most wall-mount readers.
• Wi-Fi APs (802.11ac Wave 2): 12–17 W. Wi-Fi 6E APs (tri-band): 20–30 W. Wi-Fi 7 APs (multi-link): 30–60 W — many require 802.3bt Type 3 or higher.

Building the PoE budget worksheet

A PoE budget worksheet is the design document that prevents commissioning surprises:

1. List every PoE device on the switch. Pull maximum wattage from the manufacturer spec sheet — not the IEEE standard. Use maximum, not typical, because worst-case power draw (PTZ homing after reset, AP scanning all channels, camera heater active) happens simultaneously during commissioning.
2. Sum the device watts. Add 15% buffer for firmware overhead, unexpected device additions, and future expansion. This is the required switch PoE budget minimum.
3. Check per-port standard against device requirements. If any device requires 802.3bt and the switch only provides 802.3at per-port, the switch is wrong for that device regardless of total budget.
4. Verify the switch’s total PoE budget, not just port count. A 48-port PoE+ switch does not have 48 × 30 W = 1,440 W of PoE budget. Most are 740–900 W. Fully loading all 48 ports with devices drawing 20 W each (960 W) exceeds the budget and causes port throttling.

The most common under-provisioning scenario in commercial IDF closets involves mixed-device installations where cameras, readers, and APs are all landed on the same switch and the designer selected the switch on port count alone. For multi-switch IDF closets where camera and security traffic should be logically isolated from corporate network traffic, the VLAN and switch architecture design managed by our network security services addresses both the segmentation and the PoE budget problem at design time.

Switch selection for multi-system IDF closets

For IDF closets hosting mixed camera, access control, and Wi-Fi loads, select switches against a calculated budget rather than a standard port count. A practical example for a mid-size commercial floor hosting 8 cameras (avg. 10 W), 4 access control readers (avg. 6 W), and 4 Wi-Fi 6E APs (avg. 25 W): total budget = 80 + 24 + 100 = 204 W plus 15% buffer = 235 W minimum. A 24-port switch with a 370 W total PoE budget meets this comfortably; a switch marketed as “24 × PoE+ ports” with a 185 W total PoE budget does not.

Replacing an under-spec switch after commissioning requires re-racking, re-patching on a finished floor, and often re-testing the entire IDF. The cost difference between a correctly specified switch at bid time and a switch replacement at commissioning is typically $500–$1,500 in hardware versus $3,000–$8,000 in labor and remediation. The right time to do the PoE budget math is at design development, before the switch is on the purchase order.