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Cable Voltage Drop

Check whether a power run holds up over distance and when to step up the cable size, before you roll it out. Updates live as you type.

6 · Cable Voltage Drop & Gauge

Will your run hold up over distance?

Vdrop = 2 × length × I × ρ ÷ area (ρ copper = 0.0175 Ω·mm²/m). Aim for under 5%. If over, step up a gauge.

About this calculator

Check whether a power run holds up over distance and when to step up the cable size, before you roll it out. Updates live as you type.

Questions

How do I calculate voltage drop in a cable?

Voltage drop equals 2 times the run length times the current times the resistivity of copper (0.0175 ohm-mm2/m), divided by the conductor area in mm2. The factor of 2 accounts for the current flowing out and back. Divide the drop by the supply voltage to get the percentage.

How much voltage drop is acceptable?

A common working target is to keep volt drop under about 5 percent of the supply voltage. Beyond that, sensitive gear can misbehave, motors lose torque and amplifiers lose headroom. If you are over, step up a cable gauge or shorten the run.

Does a bigger cable really help?

Yes. Voltage drop is inversely proportional to conductor area, so going from 2.5 mm2 to 4 mm2 cuts the drop by roughly a third for the same run. Over long distances the right gauge matters far more than the connector.

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