A long conductor behaves like a small series resistor
The load current must travel through metal with finite resistance. In this workbench, resistance begins with resistivity ρ, one-way conductor length L, and bare-metal cross-sectional area A. Increasing length raises resistance in direct proportion; increasing metal area lowers it. The selected circuit factor then turns that one-way conductor resistance into an effective path resistance, and Ohm's law converts the result into lost volts. The estimated load voltage is source voltage minus that calculated drop.
Percentage drop adds essential scale: the same 3 V loss is 2.5% of a 120 V source but only 0.625% of a 480 V source. It is therefore more useful to read volts and percent together than to call a raw voltage loss acceptable or unacceptable. The calculator reports arithmetic for a declared scenario; a governing code, equipment instruction, project specification, or qualified designer must supply the actual design criterion.
Audit a result from metal geometry to the receiving terminals
Keep the intermediate quantities visible so a surprising answer can be traced rather than merely recalculated.
- Verify the conductor description
AWG, metal area, and bare diameter describe conducting metal, not insulation or cable-jacket outside diameter. A nominal copper or aluminum preset is a planning value near 20 °C; use custom resistivity only when a reliable source supplies a value for the intended material and conditions.
- Check the electrical path
Enter the physical source-to-load distance once. The model applies two conductors for DC or two-wire single phase, while balanced three-phase uses its own square-root-of-three relationship. Identical parallel conductors per line divide the effective resistance only when current sharing is a valid assumption.
- Read the answer at the load
Compare drop in volts, drop as a percentage of source voltage, and estimated load voltage. If the displayed load voltage is implausible, inspect current units, length units, voltage basis, and the number of parallel paths before changing wire size.
DC, single phase, and balanced three phase are different paths
DC and two-wire single phase
The outgoing and return conductors both contribute resistance, so a one-way distance receives a factor of two. This simplified resistive path does not add AC reactance or waveform effects.
Balanced three-phase line-to-line
The calculation uses line current and the declared line-to-line source voltage with a square-root-of-three factor. It does not infer a neutral current, an unbalanced phase load, or harmonic current.
Parallel conductors
Dividing resistance by the number of identical paths assumes equal material, size, length, termination, and current sharing. The number field is not evidence that a proposed installation is permitted or properly protected.
What a resistive planning result does not certify
Voltage drop is only one design check. Keep these exclusions attached to any copied result.
- No ampacity, insulation-temperature, ambient-temperature, bundling, terminal, or overcurrent-protection decision is made.
- No inductive reactance, power-factor angle, harmonics, motor starting, transient behavior, or fault-current calculation is included.
- Nominal bulk resistivity is not a substitute for the resistance, construction, and temperature data published for the actual cable.
- The AWG geometry table identifies metal dimensions; it does not select a safe conductor or verify a local electrical-code installation.
Continue only with the quantity the next decision needs
If the load is specified in VA, watts, or power factor rather than amperes, establish the intended RMS current with the volt-amps calculator before estimating conductor drop. That handoff separates load arithmetic from conductor arithmetic and prevents apparent power from being treated as real watts.
A raceway question belongs in the conduit fill calculator, which evaluates entered conductor and raceway dimensions rather than voltage loss. For a pure power-scale change—such as reporting a compatible real-power total in millions of watts—use the megawatt calculator. None of those neighboring tools replaces cable data, protection design, or a code review; each answers a narrower quantity question.