Low-Voltage Drop Calculator

Understanding Voltage Drop in AV & Low-Voltage Installations

Voltage drop is the reduction in voltage that occurs as electrical current travels through wire. In low-voltage systems — the 12V, 24V, and 48V circuits common in AV, security, and building automation — even small drops can cause real problems. A security camera rated for 12V may fail to boot if it only receives 10.5V. A powered speaker on a long 24V run may distort or cut out. Door strikes and magnetic locks can fail to engage entirely.

The physics are straightforward: voltage drop equals current multiplied by wire resistance, and wire resistance increases with length and decreases with thickness. This calculator accounts for the round-trip distance (power must travel to the device and return), wire gauge (AWG), and material (copper has roughly 60% the resistance of aluminum). The industry rule of thumb is to keep total drop under 5%, though many professionals target 3% or less for critical systems like access control and IP surveillance.

When planning wire runs, always measure the actual cable path — not the straight-line distance. Cable routed through walls, ceilings, and conduit often adds 20-30% over the direct measurement. For long runs, consider stepping up to a higher source voltage with a local step-down converter near the device. Pair this tool with our Speaker Wire Gauge Calculator for audio-specific wiring and our Conduit Fill Calculator to make sure your chosen wire fits the pathway.