Check voltage drop on a cable run
Long 12 V runs lose volts to wire resistance — size the cable before the load browns out.
Tools used in this guide
The job
Wire has resistance; current through it burns voltage. A 12 V LED strip at the end of a long thin cable can see 10 V and dim or flicker. The 3 % rule of thumb says keep drop under ~3 % for branch circuits.
Conductor, size, length, current
Pick copper or aluminum, the conductor area in mm², the one-way run length, the current, and the system voltage. DC and single-phase count the round trip; three-phase uses the √3 factor.
Worked example
12 V, 10 A, 5 m one-way on 2.5 mm² copper: loop resistance ≈ 0.069 Ω, drop ≈ 0.69 V ≈ 5.7 % — over the 3 % line. Going to 6 mm² cuts the drop to ~0.29 V ≈ 2.4 %, inside the limit.
Where it stops
Resistivity at 20 °C is assumed — hot conductors have more resistance, so leave margin on long runs at high current. Ampacity (whether the wire overheats) is a separate check that this tool doesn't make.