Low-voltage DC voltage drop calculator
Powering a camera, an LED strip, a wireless antenna amp or a control panel down a long run? See what voltage actually reaches it.
Voltage drop
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Voltage at the device
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Power lost in the wire
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Longest run at your limit
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How it works
loop resistance = 2 × length × (Ω per 1000 ft ÷ 1000)
voltage drop = current × loop resistance
voltage drop = current × loop resistance
Current flows out on one conductor and back on the other, so the wire's resistance counts twice. 75 ft of 16 AWG is 0.6 Ω out and back. At 1.5 A that loses 0.9 V, which is 7.5% of a 12 V supply.
The calculator uses solid copper resistance at 20 °C, the same table as the 70V line calculator, extended to 24 and 26 AWG for data-style cable.
Field notes
- Higher voltage goes further. The same device at 24 V draws half the current of a 12 V version and loses a quarter of the power in the wire. If the gear accepts it, run the higher voltage.
- Check the device's input range, not just the nominal voltage. Some devices tolerate a wide range on a "12 V" input; others brown out after a small drop. The spec sheet decides your limit.
- Use the peak draw. Motors in PTZ cameras, LED drivers at full white, and devices booting up all pull more than their average current.
- Stranded and warm cable runs higher than this solid-copper figure by a few percent, and cheap copper-clad aluminum cable is far worse. Leave margin.
- Network-powered gear has its own rules. PoE budgets and cable limits are a different calculation.