PoE voltage is present. Why does the camera keep rebooting?

Is the camera restarting or only losing video?

Record the device uptime, link state and switch event log if available. A missing picture can be caused by an IP address, VLAN, NVR, stream or wireless problem while the camera remains powered. An uptime reset or a repeated boot sequence is stronger evidence of a restart, but still does not identify its cause.

Write down the time and trigger: nightfall, infrared illumination, PTZ movement, a heater, another camera starting, or an otherwise unexplained interval. Firmware faults and device defects remain possible.

Which three PoE power limits should you check?

Check the camera’s maximum demand, the individual port’s supported power and configured limit, and the switch’s shared PoE budget. A compatible port can still have insufficient available power when other devices are connected. Record the camera’s operating features and distinguish power at the supply from power reaching the device.

PSE means power-sourcing equipment, such as a switch or injector. PD means powered device, such as a camera. Power available at the PD is lower than the PSE output because cabling has losses. Keep these two measurement points separate.

Do not assume all PoE-labelled products are interoperable. Passive PoE can apply power without the standard detection process. Confirm voltage, polarity, pin use and compatibility before connecting equipment.

How do you isolate the camera, supply and cable?

Compare the same camera on a known-good short copper lead with its behaviour on the installed cable, using a compatible power source. Change only one variable at a time. Trigger the feature associated with the restart, such as infrared lighting or PTZ movement, and repeat the comparison after repair.

1. Start at the switch. Use the same camera and an appropriate known-good short copper patch lead. Trigger the failing feature and record whether the restart returns.
2. Test an appropriate alternative port or injector. Confirm its rating and account for the other loads. Change only one part of the setup at a time.
3. Reconnect the installed cable. If the issue now returns, inspect patch leads, couplers, terminations, moisture and physical damage.
4. Measure under load if supported. Record the instrument’s measurement point, class, loaded voltage and power, together with the camera’s operating mode.
5. Repeat after the repair. Use the same night/IR/PTZ conditions and other-port loads. A daytime picture alone does not verify the original problem is fixed.

What does a PoE tester prove?

An identification tester may show which pins supply power, voltage and an indicated PSE type. A load-capable instrument can additionally exercise the supply and measure loaded voltage or power. An inline meter observing a camera measures that camera’s current operating demand; it does not automatically establish the port’s maximum available power.

Fluke’s LinkIQ documentation explicitly distinguishes advertised power information from loaded voltage and power measurements. Use that distinction when comparing tools, without assuming a budget tester has the same functions.

Why can cable length and poor contacts affect PoE?

Resistance in the conductors and connections creates voltage drop under load. Poor contacts may only show their effect when demand increases. Use specified copper cabling and suitable terminations; do not treat copper-clad aluminium as equivalent merely because the packaging names the same category.

Vendor extended-PoE modes may operate beyond conventional Ethernet distances by reducing data rate or requiring compatible equipment. Document that mode rather than applying its result to standard gigabit links.

Download the field-test record to keep the equipment, cable and operating state alongside each observation.

What else should you check before relying on the result?

A test result is useful only within the instrument’s documented capability and the setup used for that measurement. Check the exact model, permitted connection state and acceptance requirement before acting on a PASS. The questions below clarify common assumptions that can otherwise turn a useful observation into an unsupported conclusion.