Voltage Drop Demo

Try a NEC-informed voltage drop calc for a single feeder run -- no signup required.

Calculation Metadata

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Inputs

Method: simplified resistive voltage drop using NEC Chapter 9, Table 8 DC resistance at 75°C. The full calculator supports multi-segment runs (taps, sub-feeders), AC reactance, and conductor selection recommendations.

System

System voltage (V) System type Load current (A) One-way length (ft)

Conductor

Material Size Ampacity basis

Results

Voltage drop 5.9V

Voltage drop (percent) 2.44%

End-of-run voltage 234.1V

Selected conductor ampacity 230.0A

Status: Selected conductor satisfies ampacity and the voltage-drop threshold.

Math window

Input summary: Vsystem=240.0 V, I=200.0 A, L=240.0 ft
Substitute values: Vdrop = 2 * 200.0 * (0.061 * 240.0/1000)
Voltage drop: Vdrop = 5.9 = 5.9
Percent drop: Vdrop% = (5.9 / 240.0) * 100 = 2.44
End voltage: Vend = 240.0 - 5.9 = 234.1
Ampacity check: Selected conductor ampacity = 230.0 at 75C. = Selected conductor satisfies ampacity and the voltage-drop threshold.
Recommendation: Minimum ampacity conductor = Cu 3/0; recommended conductor = Cu 4/0. = Voltage Drop

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Math Window

Formulas

Governing equation
```
Vdrop = 2 * I * (R_per_kft * L/1000)
```
Units: V
Percent drop
```
Vdrop% = (Vdrop / Vsystem) * 100
```
Units: %

Resistance basis assumption

Copper 4/0 uses resistance_dc_75c table value 0.061 Ohm/kft.

Units: Ohm/kft

Ampacity baseline

Ampacity is checked against NEC / NFPA 70 Table 310.16 (raceway/cable/earth) using the 75C column for the selected material. Voltage drop method: simplified resistive (R only).

Units: A

Ordered Steps

Input summary
```
Vsystem=240.0 V, I=200.0 A, L=240.0 ft
```
Units: V, A, ft

Substitute values

Vdrop = 2 * 200.0 * (0.061 * 240.0/1000)

Units: V

Voltage drop
```
Vdrop = 5.9
```
Result: 5.9

Units: V
Percent drop
```
Vdrop% = (5.9 / 240.0) * 100
```
Result: 2.44

Units: %
End voltage
```
Vend = 240.0 - 5.9
```
Result: 234.1

Units: V
Ampacity check
```
Selected conductor ampacity = 230.0 at 75C.
```
Result: Selected conductor satisfies ampacity and the voltage-drop threshold.

Units: A

Recommendation

Minimum ampacity conductor = Cu 3/0; recommended conductor = Cu 4/0.

Result: Voltage Drop

Engineering Use Notice

Calculator outputs are provided as engineering support and workflow aid. They do not replace licensed professional judgment, project-specific design review, or code-required responsibility.

See full details in the Engineering Disclaimer.