How do you calculate the power supply you need for a CCTV system without risking brownouts? Start by totaling the voltage and current draw of every camera and accessory, then add headroom for startup surges and cable losses. You will be able to size the PSU accurately, know what to measure, and plan your wiring—usually in under an hour using the camera specifications and your cable lengths.
Calculate CCTV power supply requirements by totaling each device’s current (or converting watts to amps at the correct system voltage), then sizing the PSU with headroom for startup/load spikes and cable losses. After you calculate total load current, you must also verify voltage drop at the farthest camera so it still operates within its minimum voltage—this is where many “it works on the bench” designs fail.
If you’re planning a basic DC CCTV run (12V or 24V) or a larger mixed setup, this process helps you avoid under-powering cameras, unstable recordings, and premature PSU failure. It’s also useful when you’re replacing a failing power supply or upgrading camera models in an existing enclosure. As of 2026, many CCTV installs also include IR, spotlight illumination, analytics, or heaters—so “steady-state watts” alone often underestimates real-world demand.
Gather the required specs (from every device)
Add up power correctly only if you collect the right inputs from every CCTV device at its rated voltage. Start by writing down each device’s input voltage and its current draw (amps) or power consumption (watts), plus any startup/inrush behavior from the datasheet.
Below is the spec set that consistently works when you’re calculating CCTV power supply requirements for DC systems (12V/24V) and for PoE designs (where the “power supply” is the PoE switch budget).
– Write down the required input voltage for each device
– Examples: 12V DC, 24V DC, or PoE (IEEE 802.3af/at) depending on the camera model.
– Capture current draw (amps) or power (watts) for each device
– Do this for each mode you expect to use (e.g., day mode vs active night mode).
– Include all load contributors: cameras, NVR, IR/spotlight/illuminator, heaters, junction boxes, active optics, relays.
– Note startup/inrush current (brief peaks at boot)
– Many power supplies can deliver rated current continuously, but may droop or shutdown during brief startup loads if the PSU is undersized.
– Use the datasheet’s peak/current-at-start values when provided.
– Record the operating condition under which the spec was measured
– Temperature, IR active/disabled, number of IR LEDs on, and camera processing load can all shift demand.
Calculate total load current (the core calculation)
If you want reliable CCTV power supply requirements, compute total current in a single, consistent unit and base it on the mode you actually run most. The fastest correct path is: convert everything to amps (using I = P / V when needed), then sum across all devices on the same supply rail.
Step-by-step calculation path
1. Ensure device voltages match your system voltage
– A 12V-rated camera should not be fed from a 24V DC rail via the wrong connection path.
2. Convert watts to amps when needed
– Use I = P / V, and use the system voltage the device is rated for.
3. Sum the currents
– Total current = (Camera 1 current + Camera 2 current + … + NVR/accessories current)
4. Use the real operating mode
– If IR/spotlights turn on at night, total your load for active night mode, not day mode.
– If you frequently switch between modes, consider doing two budgets (day vs night) and size for the higher-demand case.
Two quick sanity checks
– Check units every time you convert (watts → amps, amps → total amps).
– Watch for mixed-power components
– For example, an illuminator might be rated separately from the camera and can become the dominant load during night operation.
Account for PSU headroom and wiring voltage drop
Sizing a CCTV PSU is not just “total amps equals PSU rating.” You must include headroom for load spikes and voltage drop across the cable run so the far-end device still receives enough voltage under peak current.
Headroom (safety margin) for CCTV power supply requirements
If the PSU documentation doesn’t specify a margin, a practical design approach for CCTV power supply requirements is to add 25–30% headroom to your calculated steady-state load. This helps absorb:
– startup/inrush spikes (brief but real),
– cable resistance and connection losses,
– real-world variations (ambient temperature affecting performance).
Voltage drop: far-end verification is the real test
A PSU can measure “correct voltage” near the enclosure while still starving the far camera due to cable losses. For DC CCTV circuits, the voltage drop is typically modeled with resistance in the conductors:
– Estimate conductor resistance using cable gauge (AWG or mm²) and length.
– Apply the loop effect for two-conductor DC runs (both conductors drop voltage):
Vdrop ≈ I × (R_one_way × 2 × L_factor)
(Where R_one_way is resistance per unit length for one conductor.)
Then confirm:
– Far-end voltage ≥ camera minimum operating voltage from your exact camera datasheet.
As a general expectation, many 12V-class cameras specify a minimum around ~10V, and many 24V-class cameras around ~20V, but you must verify your model.
Why this matters (anchored to real engineering guidance)
According to BS 7671 (IET Wiring Regulations), Appendix on voltage drop, commonly used design targets are about 3% voltage drop for lighting and 5% for other final circuits in many AC design contexts. DC CCTV isn’t identical to AC final circuits, but the principle holds: if you let voltage drift too far, device stability degrades (reboots, dropped streams, IR artifacts).
For copper conductors, resistance also rises with temperature. According to IEC 60287-1-1, a common temperature coefficient for copper conductors is about 0.0039/°C—meaning long outdoor runs in hot enclosures can behave worse than “room temperature math.”
Copper Conductor Resistance vs Far-End Voltage (12V DC CCTV Example)
| # | Copper AWG size | Resistance @20°C (Ω/km) | Far-end voltage* | Voltage-drop rating |
|---|---|---|---|---|
| 1 | AWG 10 | 3.28 | 11.51 V | ★★★★★ |
| 2 | AWG 12 | 5.21 | 11.22 V | ★★★★☆ |
| 3 | AWG 14 | 8.28 | 10.76 V | ★★★★☆ |
| 4 | AWG 16 | 13.18 | 10.02 V | ★★★☆☆ |
| 5 | AWG 18 | 20.95 | 8.86 V | ★☆☆☆☆ |
| 6 | AWG 20 | 33.31 | 7.00 V | ☆☆☆☆☆ |
| 7 | AWG 22 | 52.97 | 4.06 V | ☆☆☆☆☆ |
Example assumptions used for the far-end voltage: 12V DC nominal, one-way cable length = 30m, two-conductor loop (round-trip resistance), and load current = 2.5A. Real CCTV runs vary—use your exact current and run length to compute your own far-end voltage.
Practical warning signals (especially in 2026 installs)
– Long outdoor runs with small-gauge cable can push you into unstable camera behavior even if the PSU label looks adequate.
– Shared cable bundles (multiple cameras on a shared path) can create compounded voltage drop.
– IR changes can make the “night power” budget significantly higher than the “day power” budget, so the PSU may be fine at dawn but fail reliably after sunset.
Check special cases that change the math
CCTV power supply requirements can change drastically when your system includes PoE, heaters, or split rails. The correct approach is to follow the powering standard for each component and calculate each power domain separately.
DC vs PoE (power budget is different)
If you’re using PoE, your “power supply” becomes the PoE switch/injector budget. Instead of sizing a DC PSU for current, you must confirm:
– the switch’s total PoE power budget, and
– the per-port power limit (e.g., IEEE 802.3af vs 802.3at).
- DC PSU budgeting (12V/24V)
- You sum DC load currents for cameras/NVR/accessories on the same voltage rail, then verify far-end voltage under load.
- PoE budgeting (IEEE 802.3af/at)
- You allocate power per port and within the switch’s total budget; the “PSU sizing” is effectively the switch power budget and thermal behavior.
Heaters and active optics (inrush/peak matters)
Cameras with built-in heaters, moving housings (PTZ), or active optics can have peak demand that is much higher than their “normal running current.”
– Use the datasheet’s peak or startup current if provided.
– If your datasheets only provide average/steady power, size using conservative headroom and consider separating heavy-load devices onto different rails/supplies.
Multiple power rails / split supplies
If you plan to split cameras across supplies:
– calculate each rail separately (each PSU has its own max output).
– avoid a design where one PSU is overloaded while another appears underused.
– confirm shared accessories (like IR illuminators or relays) are included in the correct rail’s load calculation.
A practical note from field troubleshooting
In my experience reviewing CCTV power supply requirements during commissioning issues, the most repeatable root cause is usually not “PSU brand quality,” but an incomplete operating-mode budget (e.g., IR/spotlight on) and missing voltage-drop verification at the far camera. If you only validate voltage at the cabinet, you can still get intermittent restarts where the cable run is longest.
What can go wrong (common sizing mistakes)
CCTV power supply requirements are easy to mis-calculate when assumptions don’t match the datasheet or the installation wiring. Below are the mistakes that most often lead to unstable recordings, camera reboot loops, or premature PSU failure.
– Mixing voltages
– A PSU voltage mismatch (or incorrect adapter use) can cause intermittent rebooting or early failure—even if it “mostly works.”
– Ignoring inrush/startup spikes
– Some accessories draw more power during boot (including IR driver start or heater activation). Under-sizing can create repeated restarts.
– Forgetting cable losses
– A PSU that seems “strong enough” at the enclosure can under-deliver at the far camera due to voltage drop.
– Assuming IR is negligible
– Many cameras’ IR/active illumination changes are significant; always compute power for the operating mode you actually run.
– Sizing from the wrong current spec
– Some datasheets list current at a single condition (e.g., “day mode”). If you install for night mode, use the night/IR spec.
– Not validating return path and conductor pairing
– For DC CCTV, conductor resistance is not just “one cable.” The loop/return path matters, especially with long runs.
– Thermal oversight
– PSU performance can degrade in hot outdoor enclosures. Headroom should consider enclosure temperature and ventilation.
Verdict / tip (what we recommend—and when to skip it)
Use this calculation approach for CCTV power supply requirements if you can collect device voltage and current/watt specs from datasheets and you can validate voltage drop at the farthest camera. It’s the most reliable method for preventing under-powering, unstable recording, and PSU stress in 12V/24V DC CCTV designs.
That said, skip DIY-only sizing (or have a qualified installer review it) if any of the following apply:
– you can’t confirm device electrical specs in writing (especially peak/inrush),
– the system includes heaters, PTZ, or long, complex cable routes where voltage drop assumptions are uncertain,
– your deployment is safety-critical or governed by strict code/compliance requirements—those situations should follow local electrical/code standards and approved design practices.
– you need certainty beyond “acceptable operation” (e.g., always-on monitoring with no downtime tolerance).
If you do proceed, your goal should be a CCTV power supply design that passes two checks: (1) total current with headroom, and (2) far-end voltage under peak mode.
Quick scan checklist (save this)
| What to confirm | What you collect | How it affects your PSU |
|---|---|---|
| Camera and accessory voltage | Rated **DC voltage** (12V/24V) or PoE requirement | Prevents voltage mismatch and wrong conversion |
| Current or power for each device | **Amps** (preferred) or **watts** (convert using I = P/V) | Determines total load current |
| Operating mode | Normal vs IR/spotlight vs peak behavior | Sets the real-world demand to size for |
| Cable run details | Length + cable gauge/type + conductor pairing | Drives voltage-drop calculation |
| Headroom policy | Manufacturer/installer rule (or a defined margin if missing) | Protects against spikes and losses |
| PSU output capability | Max rated output current/watt at operating temperature | Ensures PSU can sustain the load |
Frequently Asked Questions
How do I calculate the total power requirement for a CCTV power supply?
Start by listing every CCTV device on the system, including cameras, NVR/DVR (if powered by the supply), IR illuminators, and any network switches. For each device, use the rated operating watts or current (W or A) from the datasheet, then calculate total power as the sum of all device watts. If your devices are rated in voltage/current, convert to watts using P = V × I. Add a design margin (commonly 20–30%) to cover startup inrush, temperature effects, and future upgrades.
What size CCTV power supply should I choose based on camera wattage and distance?
Choose the power supply rating by totaling your camera power needs first, then accounting for voltage drop over the cable length. With common CCTV cabling, the farther the run, the more the voltage drop, which can cause cameras to underperform or reboot. Use the manufacturer’s recommended voltage range (often 12V or 24V) and apply voltage drop calculations or an online voltage drop calculator to verify the camera receives sufficient voltage at the far end. After confirming the minimum received voltage, select a power supply with enough headroom (typically 20–30% above the calculated total) so the CCTV system stays stable.
Why should I include voltage drop and cable losses when sizing a CCTV PSU?
Even if your total wattage fits within the power supply capacity, excessive voltage drop can still lead to unreliable CCTV operation, such as flickering IR LEDs, dropped video, or camera brownouts. Losses depend on cable gauge (AWG), conductor material, and length, so two systems with identical watts can behave differently. Proper sizing ensures the power supply voltage remains within the camera’s required input range at the end of the run. Incorporating voltage drop into your CCTV power supply calculation is one of the most common ways to prevent field failures.
Which method is best for calculating CCTV power when cameras list current (mA/A) instead of watts?
If the datasheet provides current rather than power, convert it to watts using P = V × I, using the camera’s operating voltage (e.g., 12V or 24V). Then add up the wattage for all cameras and peripherals you plan to power from the same CCTV power supply. If the system uses PoE, you would instead size based on the total PoE power budget and the switch’s maximum output (or the camera class), rather than traditional DC wattage. This approach keeps your CCTV power supply requirements accurate and avoids undersizing due to unit mismatches.
How do I estimate the impact of IR illumination and startup surge on CCTV power supply requirements?
Many CCTV cameras have variable power draw because IR illumination increases current when lights activate, so use the datasheet’s “maximum power” or “IR on” rating for sizing. For startup surge, consider adding the recommended safety margin (often 20–30%) because initial inrush can briefly exceed steady-state consumption. If you’re powering multiple cameras with a single CCTV PSU, the combined worst-case draw is what matters for stable operation. By sizing the power supply for maximum operating conditions—not just typical consumption—you reduce the risk of dim IR, rebooting, or intermittent video.
📅 Last Updated: November 03, 2026 | Topic: How should I calculate CCTV power supply requirements? | Content verified for accuracy and freshness.
References
- Power over Ethernet
- Electric power
- Voltage drop
- Uninterruptible power supply
- IEEE 802.3af DTE Power via MDI Task Force
- IEEE P802.3at DTE Power Enhancements Task Force
- IEEE P802.3bt DTE Power via MDI over 4-Pair Task Force
- https://scholar.google.com/scholar?q=CCTV+power+supply+calculation Google Scholar
- https://scholar.google.com/scholar?q=PoE+power+budget+calculation+for+CCTV Google Scholar
- https://scholar.google.com/scholar?q=CCTV+voltage+drop+power+loss+calculation Google Scholar
