CCTV 8 September 2026 · 7 min read
How to size a PoE switch for a CCTV system
Port count is the easy part. The number that decides whether your cameras stay up is the total PoE budget, and it is usually printed in small type.
The most common CCTV order we correct is this one: sixteen cameras, so a sixteen-port PoE switch. The port count matches, the order looks finished, and then a few cameras drop off every evening once the infrared kicks in.
Ports are not the constraint. The total PoE budget of the switch is, and it is almost always the smaller number.
af, at and bt, in plain terms
Three standards matter. Each one sets a maximum per port, and the figure at the camera is lower than the figure at the switch because the cable loses some of it on the way.
| Standard | Common name | Max at the port | Realistically at the camera |
|---|---|---|---|
| 802.3af | PoE | 15.4 W | ~12.95 W |
| 802.3at | PoE+ | 30 W | ~25.5 W |
| 802.3bt Type 3 | PoE++ | 60 W | ~51 W |
| 802.3bt Type 4 | PoE++ | 90 W | ~71 W |
Alongside those per-port limits sits a separate figure: the switch’s total PoE budget, in watts, shared across every port. A sixteen-port PoE+ switch does not give you sixteen times 30 W. It commonly gives you somewhere between 120 W and 250 W in total, and the cheaper units sit at the bottom of that range. Some budget switches also do PoE on only the first eight ports. Read the datasheet, not the box.
When the budget runs out, the switch does not warn you politely. Depending on the model it either refuses power to the last camera that asked, or it drops ports by priority. Either way you find out at night.
What cameras actually draw
Honest ranges, because datasheets vary a lot between makes and even between firmware versions of the same model:
- Basic fixed bullet or dome, modest IR: 4 to 6 W.
- Higher resolution dome with stronger IR, or a varifocal bullet: 7 to 12 W.
- Small PTZ, or a camera with heavy IR arrays: 10 to 15 W.
- Large outdoor PTZ with a long-range illuminator: 25 to 30 W, sometimes more, and these are the ones that need PoE+ or PoE++ rather than plain PoE.
The number to plan against is peak draw, not idle draw. A camera sitting in daylight at 4 W is a different load at 2 a.m. with the IR array at full output and the motor moving. Datasheets often quote both. If yours quotes one number, assume it is the optimistic one.
Heat is not the problem here, night is
In a European guide you will read about camera heaters pushing the power budget up. In Faisalabad that is not your issue. Nothing in Punjab needs a heater.
What does load your budget is infrared at night, and it loads every outdoor camera at the same time. Your CCTV system’s real peak is not a busy afternoon, it is the quiet part of the night when every IR array on the site is on together. Size for that moment. A budget that works at noon and fails at midnight is a budget that has not been sized.
Heat does still matter for the switch itself. A PoE switch delivering near its full budget in an unventilated cabinet in June runs hot and throttles or trips. Give it air, or put it somewhere with air.
Why total budget beats port count
Take twelve mixed cameras averaging 9 W. That is around 108 W at the cameras, call it 125 W at the switch once you allow for cable loss.
A cheap sixteen-port switch with a 120 W budget looks like it has four ports spare, and it has none. It is already at its ceiling and has nothing left for the two cameras you will add next year, nor for the evening when several cameras pull more than their average.
The rule we use: total up peak draw, add roughly 20% for cable loss and variation, then buy a switch whose budget is at least 1.3 times that. Spare watts are cheaper bought now than bought again later as a second switch.
The 100 metre limit is real
Ethernet, and therefore PoE, stops at 100 metres of cable. That is the whole run, including patch leads at both ends, not 100 metres of straight line on a site plan. Cable that goes up a wall, along a truss and back down eats distance quickly, and a camera on the far corner of a factory yard is usually further than it looks.
Past 100 metres you have three honest options:
- A PoE extender mid-run. Cheap and it works, but it is another box needing power and another thing to fail, and you can only chain so many.
- A second switch nearer the cameras, fed by fibre back to the rack. This is what we recommend for anything beyond a single stretched run. Media converter or SFP at each end, and the distance problem disappears.
- Move the switch. Often the neatest fix is a small PoE switch in a cabinet halfway across the site rather than everything homing to one rack.
What does not work is buying “high power” or “250 metre” cable and hoping. Some switches do offer an extended reach mode at reduced speed, which is fine for a camera, but check the switch supports it before you plan around it.
Where the NVR sits
Put the NVR where the cameras aggregate, not where the office is. Camera streams are the heavy traffic; the viewing client is light. If your uplink from a remote building is a single fibre pair, you want one NVR-bound stream crossing it, not sixteen camera streams.
Many NVRs have built-in PoE ports. They are convenient for eight cameras in a shop and limiting past that, because the NVR’s own PoE budget is usually small and its ports sit on an isolated subnet that can complicate remote access. For anything beyond a small system we would rather sell you a proper PoE switch and an NVR with a single network port.
And put the NVR and switch on a UPS. A camera system that stops recording during a load-shed is not a camera system.
Worked example: 16 cameras in a factory
Say eight fixed bullets at 6 W, six domes at 9 W, and two PTZ at 25 W.
That is 48 + 54 + 50, so 152 W at the cameras. Add 20% for cable loss and peaks: about 182 W. Multiply by 1.3 for headroom: about 237 W.
So the order is a 24-port PoE+ switch with a budget around 250 W or more, not a 16-port with 120 W. The two PTZ need ports capable of 30 W each, which PoE+ covers; if either PTZ is a large one with a long-range illuminator, check whether it wants 802.3bt and specify a switch with a few bt ports.
The 24 ports also give you the eight spare you will want within two years, plus uplinks. If any camera run crosses 100 metres, a second small PoE switch out there on fibre is cleaner than extenders.
If you send us the camera models and a rough idea of the run lengths on WhatsApp, we will work out the budget and tell you which switch to order.