CCTV Power Supply Sizing Guide: How to Calculate 12V/24V DC Requirements for Security Camera Systems

You're quoting a 24-camera job. The bid sheet has cameras, cable, connectors, NVR — and one line that says "power supply, qty 1." The integrator down the street is pricing a cheaper no-name 12V 20A brick. You're looking at a multi-channel distribution box that costs three times as much. Which one wins the bid, and which one calls you back in six months with dead channels, ghost reboots, and a recall?

CCTV power looks simple until it isn't. A single undersized PSU, a cable run that's 10 feet longer than the spec assumed, or a PTZ camera that spikes on pan — any of these will take down a zone and leave the client questioning the whole install. This guide walks through how to size a CCTV power supply properly: camera load math, voltage-drop reality, centralized vs distributed topology, when to add battery backup, and how to pick the right product the first time.

Why CCTV Power Is Different From Generic 12V DC

A CCTV system isn't a single load. It's 4, 8, 16, or 64 small loads, each at the end of its own cable run, each with its own voltage tolerance, each vulnerable to a neighbor's fault.

Three factors make it different from a generic industrial 12V job:

1. Distributed loads, shared supply. Cameras are spread across a building — a server room on the ground floor, cameras on the roof, a PTZ in the parking lot 80 meters away. One PSU feeds all of them, but they don't sit side by side.
2. Voltage drop matters at the end of the cable. A 12 V camera is usually specced for 10.8–13.2 V input. A long thin cable run can drop a full volt by the time power reaches the camera, and the symptom is a camera that reboots at night when the IR LEDs kick on.
3. PTZ cameras spike. A fixed bullet camera pulls a steady 4–8 W. A PTZ camera can triple that during motor acceleration. Sizing to steady-state only is how dealers end up with jobs that work in the daytime demo and crash the first night.

A correctly sized CCTV power supply accounts for all three — steady load, inrush headroom, and cable drop.

Step 1 — Build the Per-Camera Power Budget

Start with the published current draw on the camera spec sheet, not a guess. Typical ranges you'll encounter:

The worst-case column is the one that matters. Size for the night-time state, not the daytime brochure figure. If the camera has a heater, blower, or defroster, those kick in only below a temperature threshold — but when they kick in, they don't ask permission.

Add the worst-case current of every camera on the zone. That is your aggregate load in amps. Multiply by the nominal DC voltage (12 V or 24 V) to get watts.

Then add 25–30% headroom. This is not optional. It's the buffer for:

• Aging — capacitors lose capacity over 3–5 years
• Future cameras added to unused channels
• Simultaneous PTZ motion across multiple cameras
• Ambient temperature above the rated range

A 16-camera mix of 8 fixed bullets (0.5 A each) and 8 IR domes (0.7 A each) at 12 V:

• Steady: (8 × 0.5) + (8 × 0.7) = 9.6 A → 115 W
• With 30% headroom: 125 W minimum, round up to the next available rating (150 W typical)

For a load profile like this, a 9- or 18-channel centralized box in the 120–200 W class is the right fit. Sanyi's 9-channel centralized power distribution box (48W–120W) covers the smaller zone; the 18-channel 120W–200W box handles the full 16-camera build with spare channels for growth.

Step 2 — Do the Voltage Drop Math on Your Longest Run

This is the single most common field failure on CCTV installs. The PSU is fine. The cameras are fine. The install reboots at 2 a.m. when IR LEDs flip on, and nobody can reproduce it during the day.

Cause: voltage drop over the power cable. Twelve volts at the PSU becomes 10.6 V at the camera, the IR LED bank pushes current up by 250 mA, the voltage sags to 10.2 V, the camera's brownout detector fires, the camera reboots.

The math:

V_drop = I × R × 2 × L

where I is the current (amps), R is the cable resistance per foot (or per meter) in ohms, L is the one-way run length, and the ×2 accounts for the return leg. For a 22 AWG CCTV power lead carrying 500 mA over a 50 m run:

• 22 AWG resistance ≈ 0.053 Ω/m
• V_drop = 0.5 × 0.053 × 2 × 50 = 2.65 V

That's a 12 V rail arriving as 9.35 V. Camera is offline.

Three corrections once you see this on a plan:

1. Use thicker cable. Drop from 22 AWG to 18 AWG and the same run drops 1.05 V instead of 2.65 V.
2. Move to 24 V. The camera's DC-DC converter pulls half the current at double the voltage for the same wattage. A 0.5 A load at 12 V becomes 0.25 A at 24 V — voltage drop falls 4× (half the current, same resistance).
3. Place the PSU closer. Split the system into two zones with two smaller centralized boxes instead of one big one 70 m from the far cameras.

Rule of thumb: keep voltage drop under 5% of nominal (0.6 V on a 12 V rail, 1.2 V on 24 V). Above 10% and you will have nightly problems you cannot reproduce during a service call.

Step 3 — Pick the Topology: Centralized vs Distributed

Centralized power. One PSU (or one multi-channel distribution box) in the equipment room feeds every camera on individual home-runs. This is what 90% of commercial CCTV installs use. Advantages: one place to service, one place to back up with a UPS, one bill of materials, clean documentation. Disadvantage: long cable runs, which is exactly why the voltage-drop math above matters.

Distributed power. A local wall-wart adapter at every camera location. Advantages: short cable runs, no voltage drop, trivially easy to add a camera. Disadvantages: 16 failure points instead of 1, nobody remembers which adapter feeds which camera at 3 a.m., and every outlet you plug into needs a surge-protected circuit.

Hybrid. A centralized box per floor or per building wing, fed from the main panel, with home-runs inside the zone. This is how most medium-and-up integrators build today. A 5-channel box like the SD-CH5 series (36W–72W) handles a small zone or a single building wing; stack several across a multi-floor building and you have clean zone isolation without hand-soldering 64 wall adapters.

If you're bidding single-family residential, distributed can be the right call. If you're bidding commercial, retail, warehouse, or public-sector work, default to centralized.

Step 4 — Decide If You Need Battery Backup

Not every CCTV system needs UPS backup. Cameras on a residential DVR that loses power the same moment the house does are effectively offline either way — the NVR goes dark, the recording stops. Adding a UPS to only the cameras doesn't help.

Battery backup does matter when:

• The NVR is already on UPS and you want cameras to keep recording through outages
• Intrusion detection triggers on camera loss — some monitoring centers treat a camera blackout as a panic event, and you'd rather ride through a 30-second utility blip than dispatch police
• Liability-sensitive installs — banks, cannabis dispensaries, pharmacies, any site where gaps in footage become legal exposure
• Critical infrastructure and access control — access control panels and CCTV on the same circuit need to stay up during outages, not reboot during them

Two architectures cover most cases. First, a battery-integrated power box — a single enclosure with PSU + 12 V 7Ah battery + charge circuit. Sanyi's MJ access-control power supply follows this pattern for mixed access-control-and-camera zones where you want everything on the same battery. Second, a standard UPS upstream of a centralized CCTV box, which is the right call when the camera count is large and you're protecting against outages measured in minutes, not seconds. The standby UPS is the entry-level choice; for rooms that also house an NVR, step to an online UPS.

Step 5 — Certifications, Enclosure, and Field Ruggedness

For CCTV installs sold into commercial, retail, and government projects, the PSU almost always needs to show:

• CE / FCC — baseline for EU and U.S. commercial sale
• 3C (China Compulsory Certification) — required for mainland China installs
• RoHS — environmental compliance, demanded by most procurement teams
• UL — strongly preferred for U.S. commercial and any AHJ-inspected project

For outdoor or semi-outdoor installs (parking lots, building exteriors, loading docks), the distribution box itself should be housed in a weather-rated enclosure — or the PSU should carry its own IP rating. If you're not sure what rating you need, see our IP65 vs IP67 vs IP68 waterproof power supply selection guide.

Individual per-channel fuses matter far more than they look on a datasheet. A shorted cable on channel 7 should blow channel 7's fuse, not drop all 9 cameras. Verify per-channel protection on any centralized box you spec.

Common Mistakes We See on Bids

1. Sizing to nameplate, not worst-case. A 12 V 10 A PSU feeding ten cameras at 0.9 A each (nameplate) works on paper and fails the first cold night when IR + heater pushes the real draw to 1.3 A each.
2. Running 24 AWG alarm cable for camera power because it was cheap. Fine for 10 m runs. Catastrophic at 60 m.
3. Mixing 12 V and 24 V cameras on the same distribution box. Most centralized boxes are single-voltage output. Read the datasheet.
4. Relying on the NVR's built-in camera power outputs. NVR PoE ports are fine for small installs. For anything over 8 channels, or anywhere you need external pan/tilt/zoom, use a proper PSU.
5. Forgetting the NVR and monitor in the backup math. A camera UPS is useless if the recorder dies with utility power.

Product Selection Cheat Sheet

FAQ

Q: How many cameras can I run off a single 12V 10A power supply? A: The arithmetic answer is "however many fit in 10 A with headroom." In practice that's 10–12 fixed bullet cameras (0.5–0.7 A each, with 30% margin) or 4–5 PTZ cameras. Don't trust the arithmetic blindly — run the voltage-drop math on the longest cable first. If any run drops more than 0.6 V on a 12 V rail, either move to 24 V, upsize the cable, or split into two smaller power zones.

Q: Should I use 12V DC or 24V AC for CCTV cameras? A: Modern IP cameras almost all accept 12 V DC, and many accept a 12–48 V range (usually over PoE). 24 V AC is a legacy analog-camera standard and is still seen on older installs. The practical advantage of 24 V (AC or DC) is lower voltage drop on long cable runs. If you're designing fresh today, 12 V DC is the mainstream choice, with PoE recommended for IP cameras wherever the switch can support it. See our PoE power budget and switch sizing guide for the PoE side.

Q: Do I need a UPS for CCTV cameras, or is it enough to put the NVR on UPS? A: Depends on what "uptime" means to the customer. For most residential and small-commercial jobs, UPS on the NVR alone is enough — if utility fails, cameras going offline is fine because there's nothing to record to anyway. For installs where outages are frequent, the response is time-critical, or the monitoring center panics on camera dropout, put the cameras on the same UPS or on a battery-integrated power box.

Q: What certifications should a commercial CCTV power supply carry? A: At minimum: CE, FCC, and RoHS for most Western markets. UL 60950 or UL 62368 is strongly preferred for U.S. commercial installs. 3C for mainland China. Individual per-channel fuses are not a certification but should be on the spec sheet. For outdoor installations, verify the enclosure IP rating — indoor-rated centralized boxes installed outdoors without a weatherproof cabinet will corrode within a season.

Q: How far can I run 12V DC power to a security camera? A: It depends entirely on current and cable gauge. A 500 mA camera on 18 AWG wire is good for ~80 m before voltage drop becomes a problem. The same camera on 22 AWG is limited to ~30 m. As a rule: anything past 30 m on thin cable should either move to 24 V, go PoE, or get a local power drop. Don't guess — run V_drop = I × R × 2 × L before committing to a cable plan.

Closing Notes

A CCTV power supply spec isn't a line item. It's the difference between a system that works through its warranty and one that generates after-hours service calls. Size to worst-case current, run the voltage-drop math, pick centralized topology for anything over 4 cameras, and verify per-channel fuses on the box you select. Most field failures we see are one of five mistakes from the list above — all of them preventable at the bid stage, none of them forgivable at the punch list stage.

If you're specifying a power supply for an upcoming install and want a sanity check on your load math or cable plan, contact us with the camera count, voltage, and longest cable run — we'll point you at the right product or tell you your plan needs revision before you buy parts.