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CCTV Voltage Drop Calculator
Check whether a 12V or 24V DC camera run will actually deliver enough voltage at the camera end — or flip it around to find the maximum cable length a given gauge and current can support. Built for direct DC-powered camera runs, not PoE.
Mode
Supply & load
Voltage at camera
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How this calculator works
Enter your supply voltage, the camera's maximum operating current, the one-way cable length, and the wire gauge. The calculator looks up (or uses your custom) single-conductor resistance, doubles it to account for the outgoing and return legs of the circuit, and multiplies by the one-way length to get total loop resistance. Multiplying loop resistance by current gives voltage drop; subtracting that from your supply voltage gives the voltage actually delivered at the camera. Switch to "Maximum Cable Length" mode to run the same model backwards: given a current, gauge, and planning threshold, how far can the run go before dropping too much voltage.
What voltage drop means for CCTV cameras
Every real conductor has resistance, and current flowing through that resistance uses up some of the supply voltage before it reaches the camera — that lost voltage is the "drop." A camera at the end of a long or thin cable run can receive noticeably less voltage than what's coming out of the power supply, even though nothing is actually broken. Whether that matters depends on how much voltage the specific camera actually needs to operate reliably.
Why long cable runs cause problems
Resistance increases in direct proportion to conductor length — a run twice as long has roughly twice the resistance, and therefore roughly twice the voltage drop for the same current and gauge. This is why a camera that works fine at 50 feet from its power supply can struggle or fail at 300 feet on the same wire gauge and current: the loop resistance has grown enough that the delivered voltage falls below what the camera needs.
Why cameras may work during the day but fail or reboot at night
Many cameras draw meaningfully more current at night, when IR illuminators (and sometimes heaters) switch on. If a cable run was only ever checked against the camera's idle daytime current, the added night-time draw increases voltage drop past what was verified — and if that pushes delivered voltage below the camera's real minimum, the camera can reboot, drop offline, or behave erratically specifically after dark. Checking the run against maximum operating current, not idle current, catches this before it becomes a night-only fault that's hard to diagnose after installation.
How wire gauge affects voltage drop
A lower AWG number means a physically thicker conductor, and thicker conductors have lower resistance per foot. Lower resistance means less voltage is lost to the wire itself over the same distance and current, so upsizing the gauge is one of the standard ways to extend a run or reduce drop without changing the supply voltage. There's no single "correct" gauge for every job — it depends on your specific length and current, which is exactly what the calculator above checks.
| AWG | Ω / 1000 ft at 20°C | Approx. Ω / 100 m |
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Values are nominal copper resistance for a single conductor at 20°C (68°F), converted to an approximate per-100m figure for reference. See the temperature note below for why real-world resistance can run somewhat higher.
Why maximum operating current matters
Voltage drop scales directly with current — double the current, double the drop, all else equal. Using a camera's idle or "typical" current instead of its maximum understates the real-world drop, especially for cameras with IR illuminators, heaters, or pan/tilt/zoom motors that draw significantly more at peak than at rest. Always enter the manufacturer's maximum operating current here, not a typical or average figure, so the calculation reflects the worst case the run will actually see.
Why minimum operating voltage is manufacturer-specific
There is no universal minimum voltage that applies to every 12V or 24V camera — the real number comes from the camera's own datasheet and varies by manufacturer and model. This calculator lets you enter that number if you have it, and compares delivered voltage directly against it for the most accurate check. If you don't know it, the calculator falls back to the percentage-based planning threshold, which is a reasonable guideline but not a substitute for the camera's actual specification.
12V vs 24V DC
Both are supported here using the same resistive formula — only the supply voltage and camera's rated range differ. For the same current and cable, a 24V system experiences the same absolute voltage drop as an equivalent 12V system, but that drop is a smaller percentage of the higher supply voltage, so 24V systems generally tolerate longer runs before hitting the same percentage-based threshold. Only use a voltage your specific camera actually supports — this calculator does not model 24V AC, which requires a different impedance-based calculation this tool doesn't perform.
Using Cat5e/Cat6 for camera power
Cat5e and Cat6 cable are commonly built with roughly 24 AWG and 23 AWG conductors respectively, so the 24 AWG option above is a reasonable rough match for a single pair of Cat5e, but exact resistance still varies by cable construction and manufacturer — don't assume every Cat5e/Cat6 cable is identical. Paralleling multiple pairs to lower effective resistance is a common field practice, but it is not modeled in this calculator. If your cable's datasheet lists a known conductor resistance for the configuration you're actually using, enter it in the custom resistance field instead of relying on the default AWG value. Being able to physically run power over a Cat5e/Cat6 cable also doesn't automatically mean it's an appropriate or code-compliant choice for every camera power run — check your camera and cable specifications.
Temperature and resistance caveat
The resistance table above uses nominal copper values at 20°C (68°F), a standard reference temperature for copper wire resistance. Real conductor resistance increases as the wire gets hotter, so a run in a hot attic, in direct sun, tightly bundled with other cables, or inside conduit can run somewhat hotter than 20°C and therefore have somewhat higher real-world resistance and voltage drop than this calculator shows. Treat the result as a planning calculation for typical conditions, not a guaranteed field measurement — leave yourself some margin on long or thermally exposed runs.
DC voltage drop vs PoE
This calculator is for direct DC-powered camera runs — a fixed-voltage supply feeding a camera over two conductors. PoE installations use a different power-delivery system entirely, with the switch and camera negotiating power class and the cable carrying both data and power, so this DC loop-resistance model doesn't apply to it. PoE installations should be evaluated with the PoE Budget Calculator instead.
Worked example
Illustrative only — your actual result depends on your own supply voltage, maximum current, cable length, conductor resistance, planning threshold, and camera minimum voltage. This is one example, not a rule of thumb for every job.
12V DC supply, 0.5A maximum current, 150 ft one-way run, 18 AWG (6.385 Ω/1000 ft), 10% planning threshold, no manufacturer minimum voltage entered.
| Step | Result |
|---|---|
| Loop resistance | 6.385 Ω/1000 ft × 2 × 150 ft = 1.9155 Ω |
| Voltage drop | 0.5A × 1.9155 Ω = 0.958 V |
| Voltage at camera | 12V − 0.958V = 11.04 V |
| Drop percentage | 0.958 / 12 × 100 = 7.98% |
| Status | PASS against the 10% planning threshold (manufacturer minimum not provided) |
Common field mistakes
Recurring mistakes worth watching for: checking a run against a camera's idle current instead of its IR/heater/PTZ-inclusive maximum; treating the 10% planning threshold as if it were an electrical code requirement rather than a guideline; assuming a percentage-based PASS means the camera is guaranteed to work when its actual minimum voltage was never checked; mixing up resistance values from different temperature bases; assuming any Cat5e/Cat6 cable will behave like any other without checking its actual conductor resistance; and using a fixed-voltage DC calculation to evaluate a PoE run, which uses a different power-delivery model entirely.
Frequently asked questions
How do I calculate voltage drop for a CCTV camera?
Take the resistance of one conductor at your wire gauge, double it to account for the outgoing and return legs of the run, multiply by the one-way cable length to get total loop resistance, then multiply by the camera's maximum current to get voltage drop. Subtract that from your supply voltage to get delivered voltage at the camera. This calculator runs that exact formula for you — enter your supply voltage, current, length, and gauge above.
What wire gauge should I use for a 12V security camera?
It depends on your cable length and the camera's maximum current draw — there's no single correct gauge for every job. A lower AWG number means a thicker conductor with less resistance, which reduces voltage drop over a given distance. Use the calculator above with your actual run length and current to compare gauges before you buy cable.
How far can I run a 12V CCTV camera?
That depends on the camera's maximum current draw, the wire gauge you use, and how much voltage drop you're willing to accept. Switch to "Maximum Cable Length" mode above, enter your current and gauge, and it will calculate the longest one-way run that stays within your planning threshold (and your camera's minimum voltage, if you know it).
Why does my CCTV camera go offline at night?
Many cameras draw noticeably more current at night when IR illuminators (and sometimes heaters) turn on. If a run was only checked against daytime idle current, the added night-time draw can push voltage drop past what the camera actually needs to stay powered, causing reboots or dropouts specifically after dark. Recalculate using the camera's maximum operating current, not its idle current, to catch this before installation.
Can I use Cat5e or Cat6 for CCTV camera power?
Only with caution. Cat5e and Cat6 are commonly built with roughly 24 AWG and 23 AWG conductors respectively, which this calculator's AWG options cover for a single conductor pair — but exact resistance varies by cable construction, and this calculator does not model paralleling multiple pairs to lower effective resistance. If your cable's datasheet lists a known conductor resistance, use the custom resistance field instead of assuming a default AWG value.
Is 10% voltage drop a requirement?
No. The 10% default here is a planning guideline, not an electrical code requirement or a universal CCTV standard. It's a reasonable starting point for planning a run, but the number that actually matters is your camera's manufacturer-specified minimum operating voltage — enter it above if you have it for a more accurate pass/fail check.
Should I use 12V or 24V DC?
That's determined by what your camera supports, not by this calculator. For the same current and cable, a 24V DC system generally tolerates longer runs than 12V for the same percentage drop, since the same voltage drop is a smaller fraction of a higher supply voltage. Only use a voltage your camera is actually rated for.
Does this calculator work for PoE cameras?
No. PoE uses a different power-delivery and negotiation model between the switch and camera, not a simple fixed-voltage DC supply, so this calculator's formulas don't apply to it. Use the PoE Budget Calculator instead for switch power budget and port planning.
Related CCTV tools
Powering the camera over PoE instead? Check switch headroom with the PoE Budget Calculator. Running the install off battery backup? Size it with the Battery Backup Calculator or the Amp Hour Calculator. Also sizing network bandwidth for the same cameras? Use the IP Camera Bandwidth Calculator.