PoE camera not starting? Budget, cable and night-time load
The PoE budget is the power that the recorder or switch can deliver across all its ports together. The number of ports and this budget set the limit together: eight ports will not run eight cameras if their consumption exceeds the total wattage. If one or two cameras drop out of a finished system at night, check this first.
Why the number of ports is not enough
An eight-port PoE recorder does not handle eight cameras, it handles as many watts as the manufacturer states. If, for example, the budget is well below the sum of eight cameras' peak consumption, eight cameras will go up, start and work during the day. The manufacturer publishes both numbers: the budget on the recorder's data sheet, the consumption on the camera's. Designing the system means comparing these two numbers.
Why they drop out at night
During the day a camera draws little. At dusk, however, the infrared or white light switches on and consumption jumps. The budget can run out when the cameras switch to night mode at roughly the same time, because the same sky goes dark in front of all of them.
For night-time drop-outs, check the recorder log for the time of the drop-out, and compare the cameras' consumption, which rises with IR or heating, with the budget. The model's guide also shows how the recorder handles exceeding the budget. A daytime test with night mode off will not reproduce this fault.
How much headroom to leave
Add up the maximum consumption stated on the cameras' data sheets, not the average, and leave headroom above it. Headroom is not overcaution: longer cable runs have losses, in winter camera heating draws too, and in six months the customer will ask for one more camera. The most expensive system is the one that has to be redesigned because of a ninth camera.
If the budget is tight, the answer is a separate PoE switch next to the recorder, not one camera fewer. If the recorder has no PoE ports at all, every camera runs from a switch, and the switch's budget has to be calculated the same way.
100 metres, and what the cable takes out of it
The PoE standard's segment limit is 100 metres. That holds for solid copper cable of full cross-section with good connectors. On copper-clad aluminium (CCA) cable the voltage drop is larger, so the camera further away sometimes starts, sometimes restarts, and the fault is hard to find because it does not always show.
So do not see CCA as a saving, see it as a future return trip to the site. Above 100 metres a switch goes in the middle of the run; experimenting with extenders is not worth it.
What to do on site
If a camera does not start, go through the steps in this order. First measure whether there is power on the port. Then move the camera to another port: if it starts there, the fault may be the first port or the budget. Finally connect it on its own: if it starts alone but not together with the others, add up the consumption stated on the cameras' data sheets and compare it with the budget.
You do not have to wait for dark to test night-time drop-outs: if the model allows it, switch the cameras to night mode manually in their settings and watch whether all of them keep running.
Summary
| What to check | Where to find it |
|---|---|
| The PoE budget of the recorder or switch | on the unit's manufacturer data sheet |
| The camera's peak consumption | on the camera's manufacturer data sheet, for night mode |
| Headroom between the two | for cable losses, heating and the next camera |
| Segment length | up to 100 metres, with solid copper cable, no CCA |
| If the budget is tight | a separate PoE switch, not fewer cameras |
Our PoE calculator compares the same two numbers, if you do not feel like adding them up on site.
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