⚡ NEC 2023 · Art. 210.19

Voltage Drop Calculator — NEC 2023

Calculate voltage drop for single-phase and three-phase circuits. Verify NEC 210.19(A)(1) 3% and 5% limits instantly.

✓ Single & three-phase✓ NEC 3% / 5% compliance check✓ Wire size recommendation

Voltage Drop Inputs

NEC 2023 Art. 210.19(A)(1) — 3% branch / 5% feeder+branch

Circuit Type

System Voltage (V)

Load Current (A)

One-Way Circuit Length (ft)

Conductor Size

Conductor Material

Circuit Use

Voltage drop formula (NEC method)

Single-phase formula

VD = (2 × K × I × L) / CM
Where K = resistivity (12.9 Cu, 21.2 Al), I = current in amps, L = one-way length in feet, CM = circular mils of conductor.

Three-phase formula

VD = (1.732 × K × I × L) / CM
The √3 factor (1.732) accounts for the phase relationship in three-phase systems.

NEC voltage drop limits

NEC 210.19(A)(1) recommends (not mandates) a maximum of 3% voltage drop on branch circuits, and 5% total for the combined feeder and branch circuit. Many utilities and AHJs treat these as requirements.

Circular mils reference

14 AWG = 4,110 CM · 12 AWG = 6,530 CM · 10 AWG = 10,380 CM · 8 AWG = 16,510 CM · 6 AWG = 26,240 CM

Frequently asked questions

Is the NEC 3% voltage drop limit a code requirement or a recommendation? ▾

NEC 210.19(A)(1) states the 3% limit as a Fine Print Note (FPN), which is informational — not a mandatory code requirement. However, many utilities, AHJs, and project specifications treat it as a hard requirement. For commercial and industrial projects, always verify with the local AHJ and project specifications.

What wire size should I use to limit voltage drop to 3%? ▾

The required circular mils can be calculated as: CM = (2 × K × I × L) / (V × 0.03). For example, a 20A load at 120V running 75 feet needs approximately 6,450 CM — which is 12 AWG copper (6,530 CM). Use the Pro optimizer above to get the exact minimum wire size for any circuit.

Does voltage drop affect conductor ampacity sizing? ▾

No — ampacity (NEC Table 310.16) and voltage drop are independent calculations. Ampacity limits the maximum current a conductor can carry safely based on heat dissipation. Voltage drop may require a larger conductor than ampacity alone dictates, especially for long runs. Always check both.

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