PoE Power Budgets & Cat6 Cable Voltage Drops: The Physics Behind Camera Reboot Loops

PoE power budgeting and Cat6 cable voltage drops are key factors in preventing camera reboot loops during nighttime operations. The physics behind these issues lies in Ohm's Law, which relates the voltage drop across a conductor to the current flowing through it and the resistance of the conductor.

When cameras operate during the day, they consume only 4 to 6 Watts of power, resulting in a minimal voltage drop of just 0.8V over a 60-meter distance. This leaves the camera with a sufficient voltage of approximately 47.2V. However, as darkness falls and high-power EXIR infrared night-vision LEDs are activated, the camera's power demand increases significantly, ranging from 18 to 24 Watts.

On a 60-meter section of CCA (Copper Clad Aluminium) cable, this surge in power demand results in a substantial voltage drop of up to 4.18V.

The voltage drop becomes critical when it causes the terminal voltage to fall below the IEEE 802.3at PD (Powered Device) chips' threshold of 42V. When this occurs, the internal power converter enters an undervoltage lockout state, causing the camera to shut down. The camera's internal components then power back up, triggering the IR LEDs, and resulting in an infinite reboot loop.

To mitigate these issues, it is crucial to use pure solid copper cables, specifically Cat6 benchmarked 23 AWG solid bare copper with CAI-benchmarked specifications. Avoid any cables marked as CCA or Aluminium, as they have nearly double the resistance and significantly higher voltage drops. Employ shielded external Cat6 connectors with solid internal ground wires and form clean drip loops at masonry penetrations to prevent water from entering PoE ports.

By following these guidelines and utilizing the interactive PoE Voltage Drop Calculator available on the ADI PoE Voltage Drop Calculator web app, engineers can ensure reliable camera performance even during nighttime operations.