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CCTV basics: IP cameras, NVR, PoE budget and storage
An easy CCTV guide: IP cameras, the NVR, PoE switches and their power budget, bitrate and codecs (H.264, H.265), how to estimate recording days, and cable limits.
The parts of an IP CCTV system
IP cameras send compressed video over Ethernet to a network video recorder (NVR) that stores it on hard disks and shows live views. A PoE switch powers each camera through the same network cable, so no separate power supply is needed at the camera.
PoE and the power budget
Each PoE port can deliver a limited power (802.3af about 15.4 W, 802.3at about 30 W at the switch port), and the whole switch has a total PoE budget. If the cameras need more than the budget, some cameras do not start: video loss. Infrared night vision and heaters increase camera power.
Bitrate, codec and storage
Storage depends on bitrate: storage (GB per day) ≈ bitrate (Mbit/s) × 86 400 / 8 / 1000. Four cameras at 4 Mbit/s need about 173 GB per day, so a 4 TB disk keeps about 23 days. H.265 needs roughly half the bitrate of H.264 for similar quality; motion recording saves more.
Cables and distance
Twisted-pair Ethernet works up to 100 m per channel. Longer runs need a switch in between, a PoE extender, or fibre. Use outdoor-rated cable outside and protect it from lightning surges where needed.
Try it yourself
Open the Security tab and press “Learn step by step”: force a door to record a clip, lower the PoE budget and watch CAM3 lose power.
Open the PlantFlow 3D simulator →Safety: this guide explains principles for learning. Real installations must follow the applicable codes, the equipment manufacturer's instructions and the approval of a competent, qualified person. Isolate, lock off and prove dead before touching any circuit.