WireWicket / Field calculation 02
Single- and three-phase voltage drop
Estimate voltage drop from phase, system voltage, load, one-way run length, conductor material, and conductor size. The example values are a starting fixture, not a recommendation.
Calculation inputs
Enter a finite voltage greater than 0 V.
Enter a finite load current greater than 0 A.
Enter a finite one-way run length greater than 0 ft.
Enter a value from 0 to 1. The sine term assumes a lagging load; 0.90 is a provisional default.
Both phase modes use verified AC resistance and reactance rows for supported PVC raceways and covered conductor sizes. The power-factor sine term assumes a lagging load.
Single-phase result
- Voltage drop
- 2.92 V
- Voltage drop percentage
- 2.43%
Voltage drop ÷ system voltage × 100
Reference scope: formula and conductor-impedance sources; this calculation is not based on an edition-specific NEC table.
Project NEC edition: no project context.
Calculation inputs
- Phase
- Single-phase
- System voltage
- 120 V
- Load current
- 20 A
- One-way run length
- 100 ft
- Conductor size
- 8 AWG
- Conductor material
- Copper
- Power factor (lagging)
- 0.9
- Raceway
- PVC Schedule 40
Calculation basis
Vdrop = 2 × I × (L / 1000) × (R × PF + X × √(1 − PF²)). I is amperes, L is one-way feet converted to kft, PF is cos θ, and R/X are in Ω/1000 ft. The PF sine term assumes a lagging load.
R = 0.786 Ω/1000 ft at 75°C; X = 0.052 Ω/1000 ft at 60 Hz. No ambient or temperature correction is applied. The lookup applies to non-ferrous conduit with one conductor diameter center-to-center spacing; raceway trade size is not part of this lookup.
Southwire SIMpull THHN/THWN-2 Copper, SPEC 10000. Raceway: PVC Schedule 40.
Equation source: Southwire Power Cable Installation Guide, AC single-phase two-wire equation 6-26Impedance source: Southwire SIMpull THHN/THWN-2 Copper, SPEC 10000, Table 2 – Electrical and Engineering Data