How much voltage drop is acceptable for security devices?

The common design limit is 10% of supply voltage — 1.2V on a 12VDC circuit, 2.4V on 24V. Many cameras brown out below about 10.8V, and IR night mode is usually what fails first because it doubles the current draw.

Why do 24V devices allow much longer cable runs than 12V?

Twice the voltage means half the current for the same wattage, and twice the allowable drop in volts. Combined, a 24V circuit supports roughly four times the cable distance of a 12V circuit on the same wire gauge.

Why is the cable length doubled in voltage drop calculations?

Current flows out on the positive conductor and back on the negative, so a 50 m cable run has 100 m of copper in the circuit. Voltage drop calculations always use this round-trip length.

Cable Voltage Drop Calculator

Long cable runs quietly starve cameras, maglocks and alarm devices of voltage. Enter the wire gauge, run length and device current to see what actually arrives at the device — and the maximum run for every common gauge.

Circuit details

Supply voltage

Wire gauge

18/2 is the most common security power cable; 22 AWG for data pairs.

Cable run (one-way)

Units

Device current (mA)

Camera w/ IR ≈ 500–1000 mA @12V · maglock ≈ 500 mA · PIR ≈ 20 mA.

Max acceptable drop

Voltage at device

—

arriving at the device → —

Voltage drop—

Drop percentage—

Round-trip copper length—

Max run at this gauge & load—

Smallest gauge that passes—

Calculations use round-trip (2×) cable length and standard copper resistance at 20 °C.

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Max run reference — your load, all gauges

Maximum one-way cable run for the voltage, current and drop limit entered above:

Gauge	Max run

Why IR night mode is where voltage drop bites

A camera that idles at 250 mA can pull 800–1000 mA when its IR array fires at dusk. A run that measured fine with a multimeter at noon drops below brownout threshold the moment every camera on the site switches to night mode at once. Always calculate at the device's maximum current, not its idle draw — and remember maglocks hold continuously, so they see the full drop 24/7.

Frequently asked questions

How much voltage drop is acceptable?

Design to 10% or less of supply voltage. Many 12V cameras brown out below ~10.8V, and IR mode is usually the first thing to fail.

Why do 24V devices run so much farther?

Half the current for the same wattage plus twice the allowable drop in volts — roughly 4× the distance of 12V on the same gauge.

Why double the cable length?

Current flows out and back, so a 50 m run puts 100 m of copper in the circuit. All drop calculations use round-trip length.

Wiring a site in Toronto or the GTA?

AMT SYSTEMS LTD. designs and installs low-voltage cabling for CCTV, access control and alarm systems — engineered so nothing browns out in January.

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