PoE Switch Budget Calculator

When total connected device power exceeds the switch's PoE budget, the switch will prioritize ports based on its port-priority configuration — typically by port number. Lower-priority ports get shut down or have their power allocation reduced. In practice this means some cameras, APs or phones simply stop receiving power and go offline without warning. Always design with a 20–30% headroom above your calculated load to handle startup surge currents and future device additions.

PoE standards specify the maximum power at the switch port. Cable resistance causes voltage drop and power loss over the cable run — especially at longer distances. The device receives (and can use) slightly less than what the switch delivers. A standard 802.3at port delivers up to 30W, but the device only receives up to 25.5W after cable losses. For accurate planning, always use the device's measured power consumption from its datasheet, not the maximum standard value.

Only if the camera can operate at PoE+ (30W) power levels. IEEE 802.3bt Type 3/4 devices are backward compatible — they negotiate down to the switch's capability. However, if the device needs more than 30W (common for thermal cameras, high-power PTZ, or video conferencing units), it simply won't power on. Always check the minimum power requirement on the device datasheet, not just the maximum.

Cat5e/Cat6 cable has resistance of approximately 9.38Ω per 100m per conductor. At 50m, a PoE device drawing 12W experiences roughly 0.5–1.5W of cable loss. At the maximum 100m cable run, losses can reach 2–6W depending on current draw. For high-power 802.3bt devices drawing 60W, a 100m run can lose 5–8W — potentially causing the device to operate at reduced performance or fail to power up. Use higher-gauge cable (Cat6A) for long runs with high-power devices.

PoE switches are almost always preferable for new installations: they simplify cabling (one cable per camera), allow centralized management, support LLDP/CDP power negotiation for accurate budget allocation, and are typically more cost-effective per port at scale. Midspan injectors (PoE injectors) make sense when: retrofitting existing non-PoE switches, powering a single device in a remote location, or needing a PoE standard the existing switch doesn't support. For NVR/DSS Pro deployments, PoE switches on a dedicated camera VLAN are strongly recommended.

UPS VA rating must cover the total power draw of the switch, which includes the switch's own processing power (typically 15–50W for managed switches) plus the total PoE power delivered to all connected devices. For example, a 370W PoE budget switch with 40W switch overhead draws ~410W total at full load. At 0.8 power factor, that requires a minimum 510VA UPS. Add 25% headroom → 640VA. The UPS Runtime Calculator will give you precise runtime estimates for any load and battery configuration.