12V CCTV Power Supply: Sizing & Amps 2026

Getting the amps right on a 12V CCTV power supply

Size a 12V CCTV power supply by adding up each camera's real current draw (not just its "typical" figure), adding roughly 20-25% headroom for inrush and IR-LED load, then matching the total to a PSU or fused distribution box rated above that number. Get the amps wrong and you find out at 2am when the IR LEDs kick in and a camera reboots — not when you tested it in daylight.

This guide gives UK installers a straight method: work out real per-camera draw, add sensible headroom, and choose between a single boxed PSU or a fused distribution box without guesswork. Get this right once and you won't be back on site chasing a "faulty camera" that was actually just underpowered.

Sizing a 12V CCTV Power Supply: Amps per Camera, Fused vs Boxed Distribution

Size a 12V CCTV power supply by adding each camera's IR-on current draw (not idle draw) plus a safety margin, then choosing fused or single-boxed distribution based on how much fault isolation matters. A typical 12V camera idles at 0.3–0.5A but jumps towards 0.7–1A once IR LEDs and any internal heater kick in at night. Size a 4-camera run on idle figures alone and it will brown out after dark.

Working out the amps

Four cameras at a worst-case 0.8A each is 3.2A of real demand. Cable volt-drop erodes usable voltage further down a long run, so that 3.2A figure understates what you actually need at the far end.

Sizing on paper closer to 4–5A total gives headroom rather than running a PSU at its rated ceiling continuously, which shortens its working life. Continuous full-load running is the single biggest cause of early PSU failure we see reported on installer forums.

A single 12V 3A CCTV Power Supply with 4-Way Splitter suits two lighter cameras from one mains outlet. Four IR cameras on full power need more headroom than 3A gives you.

Fused box vs single boxed PSU

A fused distribution box isolates one faulty camera or shorted cable without dropping the whole run. Each channel carries its own PTC fuse, so a fault on channel 3 doesn't take out channels 1, 2 and 4.

The 18 Channel 12V CCTV Power Supply 15A Fused Box (£31.04) gives 15A across 18 fused outputs.

How Many Amps Does a 12V CCTV Camera Actually Draw?

A typical 12V analogue, HD-TVI or AHD camera draws around 0.3–0.5A at idle, rising to 0.5–1A once infrared illuminators and any built-in heater switch on. Always size the power supply for that higher figure, not the "typical" number printed on the datasheet.

Daytime, IR off: most dome and bullet cameras sit at roughly 150–350mA when there's enough ambient light and the IR LEDs stay dark. This is the figure manufacturers usually lead with, which is exactly why it's misleading for sizing purposes.

Night-time, IR on: as soon as the photocell triggers the infrared array — and, in cold outdoor enclosures, a heater kicks in too — draw can roughly double. This jump from idle to IR-on is the single most common reason installers see cameras browning out or rebooting overnight.

That's true even though the same camera worked fine on the bench in daylight.

Inrush at switch-on: capacitive input stages pull a brief surge of current higher than steady-state draw the instant power is applied. A decent 12V power supply shrugs this off. On a shared multi-way box it can occasionally trip an undersized PTC fuse on that channel, especially if several cameras power up simultaneously after a mains cut.

Rule of thumb for sizing: where you don't have a datasheet to hand, budget 0.75–1A per camera rather than the idle figure. On an 18-way box that adds up fast — our own 18 Channel 12V CCTV Power Supply 15A Fused Box gives 15A across 18 fused channels, so at 0.75A a camera you're already close to its limit with a full run of cameras, which is why we'd rather see installers under-fill a box than max it out on paper capacity alone.

What Size 12V Power Supply Do I Need for My Camera Count?

Total the worst-case current per camera with infrared illuminators running, add at least 20% headroom, then round up to the nearest PSU or power box amp rating. A datasheet's "typical" current figure is usually measured with IR off.

Every camera on a run switches to night mode at roughly the same time, which is exactly when a marginal supply sags or trips. That's the calculation most sizing mistakes skip.

Using a common IR-on estimate of 0.75A per camera, four cameras draw 3A raw. Add 20% headroom and that becomes 3.6A, so a 4A supply is the bare minimum and a 5A unit leaves safer margin for cable losses and ageing capacitors.

Eight cameras at 0.75A each draw 6A raw, or 7.2A with headroom. That rules out a single 5A adapter and points to an 8A-plus multi-way box instead.

Cameras (IR-on @ 0.75A each)	Raw total	+20% headroom	Suggested PSU
1	0.75A	0.9A	2A single adapter
4	3A	3.6A	4A–5A
8	6A	7.2A	15A multi-channel box
16–18	12–13.5A	14.4–16.2A	20–30A multi-channel box

Matching the numbers to real kit

For a single camera or a small four-way splitter run, our 12V 3A CCTV Power Supply with 4-Way Splitter covers the 0.9A–3.6A range comfortably from one mains outlet. It's CE and UKCA certified and powers up to four cameras from a single UK plug.

Why Do Cameras Drop Out or IR Wash Out at Night on an Undersized PSU?

Voltage sagging under load is the usual culprit: as IR LEDs and heaters draw more current, resistance in the cable pulls the voltage at the camera below its working minimum, so the image whites out or the unit reboots. This is a volt-drop problem as much as an amp-rating one. A PSU can be rated correctly on paper and still fail once you account for cable losses.

Symptom: IR wash-out or a dim image at night

Bleached or dim footage as soon as IR kicks in usually means the camera is under-volted, not starved of amps. Measure DC voltage at the camera's power terminals after dark, not just at the PSU output. A unit reading a healthy 12V at the box can sag to 10.5V or lower by the time it reaches the camera, and most IP and HD analogue cameras expect somewhere around 11–13V DC to hold a clean image.

Symptom: camera reboots the moment IR triggers

Current draw spikes the instant IR LEDs switch on. A marginal power supply or thin cable can't hold voltage through that transition, so the camera browns out and reboots.

This is common where several cameras share one central PSU box that's sized close to its rated total. An 18 Channel 12V CCTV Power Supply | 15A Fused Box — rated at 15A across 18 fused channels — run near full load with no spare capacity is a typical example.

The cable volt-drop rule

Longer runs on thin two-core cable — typical of budget leads bundled with cheap cameras — lose more volts before reaching the camera. Halving the cable's cross-sectional area roughly doubles the volt-drop for the same run length.

Fused Distribution Box or Single Boxed PSU — Which Suits Your Site?

A fused multi-channel box isolates faults per camera, while a single boxed PSU is simpler and cheaper but lets one fault take down every camera it feeds. The right choice comes down to camera count and how much downtime a single fault can cause on that site.

Single boxed PSU (1–4 cameras)

For a driveway, a shop entrance or a handful of cameras on one wall, a single boxed 12V power supply is the cheapest and easiest option to specify. Fewer parts means fewer things to fail, and a straight swap-out takes minutes if the unit does die.

The trade-off is that a short in one cable run, or water ingress at one camera, can drop the whole supply. That takes every camera on it offline at once — an acceptable risk on a small, low-value site but not on anything larger.

Our 12V 4A CCTV Power Supply with UK Plug, priced at £8.04, and the 12V 3A CCTV Power Supply with 4-Way Splitter, which powers up to four cameras from one mains outlet, both suit this bracket.

Fused multi-channel distribution box (5+ cameras)

Once a site runs five or more cameras, a fused CCTV power supply box earns its keep by containing a single cable fault to one channel instead of the whole run. Each output carries its own PTC fuse, so a shorted cable trips only that channel while every other camera on the board stays live and recording.

That per-channel isolation matters most overnight, when a fault can otherwise sit undetected until someone checks the footage the next morning.

Recommended kit

For the setup above, this is the kit we'd fit from our own range:

• 12V 3A CCTV Power Supply with 4-Way Splitter — 12V regulated power supply for CCTV cameras with built-in 4-way splitter. Powers up to four cameras from one UK mains outlet. CE and UKCA certified.
• 18 Channel 12V CCTV Power Supply 15A Fused Box — 18-channel CCTV power supply box with 15A capacity and PTC fuse protection per channel. Converts 100–240V AC to regulated 12V DC for multi-camera surveillance.
• 18-Channel CCTV Power Supply 12V 30A Box — 18-channel CCTV power supply with 12V DC 30A output, individual PTC fuse protection per channel, and metal lockable enclosure for centralised multi-camera
• BU240 250W Switching Power Supply 12V 20A CCTV — 250W switching power supply for CCTV: 12V 20A, 16 fused channels, battery backup charging, lockable metal case for multi-camera surveillance systems.