CCTV Cable Voltage Drop: Why Your Camera Works in Day but Fails at Night
The CCTV camera works perfectly during the day. But when it gets dark, the image turns black, the camera restarts, or the IR night vision simply stops working.
This is a very common complaint, and one possible cause is voltage drop in the power wiring. At night, the camera's IR LEDs switch on and the camera draws more current. On a long run, a thin conductor, or a poor connection, that extra current can pull the voltage reaching the camera below what it needs to operate. It is not the only possible cause, though, and we will cover the others too so you can troubleshoot properly instead of guessing.
What Is Voltage Drop in a CCTV Cable?
Every cable has some electrical resistance. When current flows through it, a part of the supply voltage is "used up" along the way. That lost portion is voltage drop.
Simply put: the power supply may output 12V, but the camera at the far end may receive less than 12V. The difference is the voltage drop. It depends on:
- Voltage at the power supply – where you start from
- Cable length – longer cable means more resistance
- Conductor size – thinner conductors have higher resistance
- Conductor material – different materials have different resistance
- Current load – the more current the camera draws, the bigger the drop
Why Does CCTV Voltage Drop Increase With Distance?
Voltage Drop = Current × Resistance
Vdrop = I × R
Resistance (R) is not fixed – it changes with the cable itself:
- Resistance increases as cable length increases. Double the length, and you roughly double the resistance.
- Resistance decreases as the conductor's cross-sectional area increases. A thicker conductor lets current pass more easily.
Since power flows out to the camera and back to the supply, both the positive and negative conductors are in the path. So a 50 m cable run actually means about 100 m of conductor in the circuit. This detail is often missed while calculating.
Why Does the CCTV Camera Fail Only at Night?
During the day, the IR LEDs are off and the camera draws relatively less current. At night, the IR LEDs turn on, and the current demand goes up. Higher current means a bigger voltage drop (remember Vdrop = I × R), so the voltage reaching the camera falls further.
If that voltage falls below the camera's acceptable operating range, you may see:
- Black screen at night
- Camera rebooting again and again
- Flickering image
- IR LEDs not working or turning off
- Intermittent video
- Camera going offline
- Unstable night vision
How Cable Quality Affects CCTV Voltage Drop
Here we are only looking at resistance and voltage drop. For the complete material comparison, see our guide on 3+1 CCTV cable: pure copper vs CCA.
- Pure copper vs CCA: CCA (copper-clad aluminium) has higher resistance than pure copper of the same size. So for the same length and current, CCA will generally show more voltage drop.
- Conductor size: A thin power conductor, whatever the material, has more resistance. Check the actual conductor size, not just how thick the outer cable looks.
- Cable length: Longer run, higher resistance, higher drop.
- Power conductor gauge: In combo cables, the power cores are often much thinner than the video core is, so their gauge deserves specific attention.
Does 3+1 CCTV Cable Have a Voltage Drop Problem?
A 3+1 cable carries video and power in one jacket. The power part is usually a 2-core conductor pair, and its size matters a lot because it carries the full camera current. Any 3+1 cable, like any cable, will have some voltage drop. Whether it becomes a problem depends on the situation:
- Short runs: Voltage drop is usually small and often not an issue with lower-power cameras.
- Medium runs: Drop becomes noticeable, especially with IR cameras at night. Conductor size and material start to matter.
- Long runs: Drop can become significant. A cable that works at short distance may fail here, so power design needs extra care.
There is no single maximum distance that works for every setup. Actual performance depends on supply voltage, camera current draw, conductor size, cable construction, connector quality and the camera's accepted input range. For more on distance planning, see how far you can run a CCTV cable.
How to Calculate CCTV Cable Voltage Drop
The example below is hypothetical and only for understanding the method. Use your own camera's actual specifications for real calculations.
Vcamera = Vsupply − Vdrop
where Vdrop = I × R
| Variable | Hypothetical Value | Meaning |
|---|---|---|
| Vsupply | 12 V | Output of the power supply |
| Cable run (one way) | 50 m | Distance from supply to camera |
| Conductor size | 0.5 mm² copper | Cross-sectional area of each power conductor |
| Resistance (R) | about 3.5 Ω | Approx. for 100 m total conductor length (out and back), using copper resistivity of about 0.0175 Ω·mm²/m |
| Camera current (day) | 0.3 A | IR LEDs off |
| Camera current (night) | 0.5 A | IR LEDs on |
Daytime: Vdrop = 0.3 × 3.5 = 1.05 V, so Vcamera = 12 − 1.05 = about 10.95 V
Night: Vdrop = 0.5 × 3.5 = 1.75 V, so Vcamera = 12 − 1.75 = about 10.25 V
Now suppose this hypothetical camera needs at least 10.8 V to work properly. In the daytime it gets 10.95 V and works. At night it gets 10.25 V, which is below the minimum, and it may restart or lose IR. That is exactly the day-works-night-fails pattern. If the same run used a thinner or higher-resistance conductor, the drop would be even larger.
Please do not treat these numbers as a rule for any real camera. Always take the actual voltage range, current draw and conductor data from the manufacturer's specifications.
How to Check Voltage at the Camera
Safety: Use a suitable multimeter set to DC voltage, take care of correct polarity, and avoid shorting the probes across the connector pins. If you are not comfortable, get a qualified technician to do it.
- Measure voltage at the power supply output, with the camera connected.
- Measure voltage at the camera end during daytime.
- Turn on or wait for IR night mode. You can cover the camera's light sensor to trigger it, if the model allows.
- Measure again under load with IR on. Note the difference from the daytime reading.
- Compare readings with the camera manufacturer's required input voltage range.
- Inspect connectors and joints for looseness, heat marks, corrosion or poor crimping.
- Check cable length and conductor size against the camera's current requirement.
A big gap between supply voltage and camera voltage under load points to a wiring or connection problem. If voltage at the supply itself sags when the camera turns on IR, the power supply may be weak or overloaded.
How to Fix CCTV Voltage Drop
- Use an appropriate conductor size for the camera current and run length.
- Use genuine copper where required – lower resistance for the same size.
- Shorten the power run where the layout allows.
- Use a suitable power supply with enough capacity for all connected cameras plus margin.
- Improve connectors and terminations – solid crimps, clean contacts, good quality DC connectors.
- Avoid unnecessary joints – each one adds resistance and a possible failure point.
- Use a local power supply near the camera where appropriate, so only the video runs the long distance.
- Redesign long-distance installations instead of stretching a design beyond what it can support. See our long-distance CCTV cable guide for options.
- Use proper voltage distribution solutions where the equipment supports them.
CCTV Voltage Drop vs Signal Loss: What's the Difference?
| Factor | Voltage Drop | Signal Loss (Attenuation) |
|---|---|---|
| What it affects | Power reaching the camera | Video or data transmission quality |
| Typical symptoms | Reboots, black screen, IR failure, camera offline | Noisy, faded, unstable or missing picture |
| Main causes | Long run, thin or high-resistance conductor, high current, poor connections | Long run, cable/shielding quality, connectors, interference |
They are different problems, and both can occur in the same installation. Fixing one does not automatically fix the other.
Common CCTV Power Problems Installers Should Check
- Thin power cable
- Long cable run
- CCA conductor
- Loose DC connector
- Poor crimping
- Overloaded power supply
- Damaged cable
- Water ingress at joints or connectors
- Multiple cameras sharing an undersized power supply
- Incorrect supply voltage
CCTV Voltage Drop Troubleshooting Checklist
| Problem | Possible Cause | What to Check | Possible Solution |
|---|---|---|---|
| Black screen only at night | Voltage falling under IR load | Camera voltage with IR on vs off | Thicker conductor, shorter run, local power supply |
| Camera rebooting at night | Voltage below minimum when IR turns on | Voltage at camera under load; supply capacity | Improve wiring or replace weak power supply |
| IR LEDs not working | Low voltage, or faulty IR LEDs | Voltage at camera; test camera on a short known-good cable | Fix power path, or repair/replace the camera |
| Flickering or intermittent video | Loose connector, poor crimp, damaged cable | Connectors, joints, cable condition | Re-terminate, replace damaged section |
| Multiple cameras fail together | Overloaded or undersized power supply | Total camera current vs supply rating | Higher-capacity supply or split power distribution |
| Problem worsens on longest runs | Cable resistance, thin or CCA conductor | Cable length and actual conductor size/material | Better conductor, shorter power run, local power |
| Problem after rain | Water ingress in connector or joint | Outdoor joints and connector sealing | Dry, re-terminate and properly protect connections |
Frequently Asked Questions
What causes voltage drop in CCTV cable?
Cable resistance combined with current flow. Longer runs, thinner conductors, higher-resistance materials, poor joints and higher camera current all increase the drop.
Why does my CCTV camera work during the day but not at night?
At night the IR LEDs switch on and the camera draws more current. If voltage drop, a weak power supply or a poor connection leaves too little voltage at the camera, it can go black or restart. Other causes like faulty IR LEDs are also possible, so measure before deciding.
How do I check voltage drop on a CCTV camera?
Measure DC voltage at the power supply and at the camera, with IR on, using a multimeter. The difference is the voltage drop. Compare the camera-end reading with the manufacturer's required input range.
Does longer CCTV cable cause voltage drop?
Yes. Resistance increases with length, so for the same current and conductor size, a longer run has a larger voltage drop.
Does pure copper reduce voltage drop?
Pure copper has lower resistance than CCA of the same size, so it generally gives lower voltage drop. Conductor size and cable length still matter just as much.
Can CCA cable cause CCTV camera power problems?
It can contribute, because its higher resistance leads to more voltage drop on longer runs or higher-current cameras. It does not automatically fail in every installation, but it leaves less margin.
What cable size is suitable for long-distance CCTV?
There is no single size for all cases. It depends on cable length, camera current draw, supply voltage, acceptable voltage drop and the manufacturer's specifications. Calculate for your actual camera and run.
Can a 3+1 CCTV cable have voltage drop?
Yes, like any cable. The power cores' size and material, along with run length and camera current, decide how significant it is.
Why does CCTV camera keep restarting at night?
A common reason is voltage falling below the camera's minimum when IR turns on. Weak power supply, loose connectors or a damaged cable can also cause it, so check voltage under load.
Can a weak power supply cause CCTV night vision problems?
Yes. If the supply cannot deliver the extra current when IR LEDs switch on, its output voltage can sag and the camera may restart or lose night vision, even with good cable.
Conclusion
If a CCTV camera works in the day but fails at night, check the voltage at the camera under IR load before replacing anything. Voltage drop from long runs, thin or high-resistance conductors and poor connections is a common cause, but a weak power supply, loose connectors or a faulty camera can look identical.
- Measure supply voltage and camera voltage with IR on
- Calculate with your actual camera current, run length and conductor size
- Fix the power design – conductor, length, supply, connections – rather than guessing
Planning a CCTV installation with longer runs? Explore JUAA's CCTV cable range and choose conductor size and material according to your camera and distance.
Explore JUAA CCTV Cable