Estimate voltage drop and load voltage for single-phase and three-phase circuits.
⛔ High-Risk Engineering Notice:
This tool estimates values using generalized standards and assumptions. Site conditions, installation methods,
conductor grouping, ambient temperature, tolerances, and code interpretations can materially change the final
result. Treat these outputs as a preliminary engineering aid and perform project-specific verification against the
governing code, manufacturer data, and a qualified engineer before field use or procurement.
A commonly cited NEC-oriented guideline is to keep branch-circuit voltage drop to 3% or less, with total feeder plus branch-circuit voltage drop often kept to 5% or less.
This calculator uses system phase, source voltage, load current, conductor size, conductor material, and one-way distance to estimate voltage drop, percentage drop, and load voltage.
Voltage drop is the reduction in voltage in an electrical circuit between the source and the load. It is caused by the inherent impedance—primarily resistance—of the conductors carrying the current. The National Electrical Code (NEC) Section 210.19(A) Informational Note No. 4 recommends that the total voltage drop for a branch circuit should not exceed 3%, and the combined voltage drop of feeder and branch circuit should not exceed 5%.
For Single Phase (1φ): Vd = (2 × L × I × R) / 1000 — The factor of 2 accounts for the round-trip distance of current flow through both the hot and neutral conductors.
For Three Phase (3φ): Vd = (1.732 × L × I × R) / 1000 — The square root of 3 (≈1.732) factor accounts for the phase angle differences in a three-phase system, where current flows through multiple conductors with 120° phase separation.