Free tool · UK
PoE & voltage drop calculator
Two checks for one camera run, made before the cable is installed. PoE: the 100m cable limit and the device power budget. 12V DC: the voltage lost in the copper. Where a run fails, the result states the remedy.
Pass
- Length: 30m. Within the 100m Ethernet limit.
- Power: 6W required; 802.3af (PoE) allows 12.95W per device. Headroom: 6.9W.
- Switch total: eight cameras at full draw exceed the combined PoE output of many 8-port switches. Check that figure separately.
PoE switches stocked
All networking products- 4 port4 Port Gigabit POE Extender 1000M Network Switch Repeater IEEE802.3af/at Plug&Play for PoE Switch NVR IP Camera AP£14.20
- 8 portHikvision DS-3E0510P-E 8-Port Gigabit PoE Unmanaged Network Switch£76.57
- 9 portHikvision DS-3E0109P-E/M 9-Port PoE Switch 8×PoE 100Mbps Long Range 300m£54.94
- 16 portHikvision DS-3E0318P-E/M(B) 16-Port PoE Unmanaged Network Switch£194.70
- 24 portHikvision DS-3E0326P-E/M(B) 24-Port PoE Unmanaged Network Switch£196.90
The constraint is the total PoE budget, not the port count. Compare the sum of your camera draws with the switch total; the per-port rating does not show it.
Method and limits
PoE limit: 100m over Cat5e/Cat6. Device budget, set by the standard and measured at the camera: 802.3af gives 12.95W, 802.3at 25.5W and 802.3bt 51W. The limit most often exceeded is the switch total, not a single camera. Sum the draw of every camera and compare it with the whole-unit PoE budget of the switch; the per-port rating alone does not answer the question.
At 12V DC, copper resistance sets the limit. Voltage drop is proportional to the loop length, which is twice the run length (out and back). One step up in conductor size halves the drop. Typical camera tolerance: about −10% (10.8V). Night-time draw: up to double the daytime figure once the infrared switches on, so a run that passes at 3pm may brown out at midnight. Remedies for a failed run: PoE, 24V equipment, a PSU closer to the camera, or thicker cable.