PoE Not Working? A Six-Step Fault-Finding Path for CCTV Switches

"The camera has no power" describes a symptom, not a fault. In practice there are six distinct causes, and they are best eliminated in a fixed order, because each step narrows what the next one can be. Doing it in this order usually takes ten minutes; doing it at random can take a day.

1. Confirm the port is really a PoE port

It sounds trivial and it is the most common mistake on mixed switches. Ports are often grouped — for example 8 PoE ports plus 2 uplinks — and the uplink ports will never supply power. Check the port numbering on the front panel, not the marketing headline ("8-port PoE switch" may mean 4 PoE + 4 uplink).

• Look for a PoE symbol or a coloured group on the panel.
• Check whether the port is in a "PoE enabled" group in the web UI.
• Confirm the port standard (af / at / bt) against the camera class.

2. Watch what the port reports during negotiation

A working PoE port runs a short detection-and-classification sequence before it applies power. Managed switches show this in the port status: detecting, class X, power good, or denied. If the port reports "denied" or "class 0" for a camera that should be class 4, the answer is usually the camera or the cable, not the switch.

3. Check the total budget, not just the port

PoE budget is shared. A 120 W switch with eight 15 W cameras is at its ceiling before any headroom, and the ninth camera gets refused even though its own port has capacity. Add the switch's own consumption, then keep 25–30% headroom for night draw.

• Sum night draw (IR on), not bench draw.
• Compare against usable budget, which is usually lower than the label wattage.
• If the budget is the cause, split the cameras across two switches rather than buying a bigger one you do not need.

4. Test the cable properly

PoE is sensitive to resistance in a way data-only Ethernet is not: the camera may link fine and still brown out under load. Copper-clad aluminium (CCA) cable, long runs, poor crimps and water in a connector all show up as voltage drop rather than as a dead link.

• Measure voltage at the camera end under load, not open-circuit at the switch.
• Check for CCA: cut a strand — aluminium is white and brittle, copper is copper-coloured and ductile.
• Test at 100 m maximum, and remember that a run measured "about 90 m" with a wheel is often 105 m.
• Re-terminate before replacing; a bad crimp looks exactly like a bad camera.

5. Isolate the PD

Put the suspect camera on a known-good port with a short patch lead. If it powers up there, the camera is fine and the fault is in the run, the port or the budget. If it fails on a good port, check whether the camera needs more than the port offers — a heated PTZ on an af port will not run, however good the cable.

6. Then look at configuration

Only after the electrical path is proven should you touch software. The usual culprits: PoE disabled per port, a per-port power limit set too low, a scheduled port shutdown, or a storm of spanning-tree / loop events that bounced the port.

Managed units with per-port class reporting make steps 2 and 3 fast, which is the practical argument for the L2/3 managed PoE range on larger sites. For small cabinets the unmanaged PoE switches are enough — you just diagnose with a meter instead of a UI.

Send the camera model, the run length and the switch model, and we will tell you whether the port can carry it. Ask for a quote.

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