Voltage Drop Calculator
Input Parameters
Calculation Results
Voltage Drop
Percentage Drop
Step-by-Step Calculation
Engineering Analysis
Enter parameters and click Calculate to see results
What is Voltage Drop Calculator?
Voltage drop calculation determines how much voltage is lost along a cable due to conductor resistance, load current, power factor, length, and temperature, ensuring equipment receives sufficient voltage (typically ≤3% for lighting circuits and ≤5% for power circuits per NEC Article 210.19(A) and IEC recommendations). The Voltage Drop Calculator (also known as NEC voltage drop calculator, three phase voltage drop calculator, cable voltage drop calculator online, long run voltage drop calculator, single phase voltage drop calculator) supports Copper and Aluminum conductors, AWG/mm²/kcmil sizes, single-phase and three-phase systems, custom conductor properties, and automatic temperature correction using NEC Chapter 9 Table 8 resistance values.
This calculator provides special features like relevant visualization (live compliance gauge, resistance bar chart, voltage distribution path diagram), has a dedicated section for comments, analysis and recommendations (practical implications, upsizing suggestions, energy loss notes, and installation best practices), provides step-by-step calculation (transparent audit trail of every formula and correction factor), user can download/export results in CSV (complete professional engineering report with inputs, calculations, and compliance status), and has another special feature of Colorblind view for improved accessibility (high-contrast mode with bold outlines and patterns).
Related Calculators
How to use Voltage Drop Calculator
Purpose Quickly verify if a cable run meets code voltage drop limits, calculate actual load voltage, determine required conductor upsizing for long runs, and ensure equipment performance, efficiency, and safety in residential, commercial, industrial, or solar PV installations.
Every input explained
- System Voltage (V) – Nominal AC supply voltage (e.g., 120 V, 240 V, 480 V, 400 V)
- Phase Type – Single Phase or Three Phase
- Load Current (A) – Actual operating current drawn by the load
- Conductor Length – One-way distance from source to load (meters or feet)
- Conductor Material – Copper or Aluminum
- Conductor Size – Standard AWG/mm²/kcmil or Custom Size
- Power Factor (cosφ) – Load power factor (0.01 to 1.0, default 0.85)
- System Standard – NEC (North America) or IEC (International)
- Ambient Temperature (°C) – Installation environment temperature (optional, default 20°C)
Voltage Drop Formula
\(\text{Voltage Drop (1-Phase)} = 2 \times I \times R \times L \times \cos\phi\)
\(\text{Voltage Drop (3-Phase)} = \sqrt{3} \times I \times R \times L \times \cos\phi\)
\(%\text{Voltage Drop} = \frac{\text{Voltage Drop}}{\text{System Voltage}} \times 100\)
\(\text{Load Voltage} = \text{System Voltage} – \text{Voltage Drop}\)
\(\text{Corrected Resistance} = R_{\text{base}} \times k_{\text{temp}}\)
\(k_{\text{temp}} = 1 + \alpha \times (T_{\text{ambient}} – T_{\text{base}})\)
Where:
= load current (A)
= conductor resistance (Ω/km, corrected for temperature)
= one-way conductor length (km)
= power factor
= temperature coefficient (0.00393 for Copper, 0.00403 for Aluminum)
= installation temperature (°C)
= 20°C reference temperature
How to Calculate Voltage Drop (Step-by-Step)
- Enter System Voltage, Phase Type, Load Current, and Conductor Length.
- Select Conductor Material and Size (standard AWG/mm²/kcmil or custom area/resistance).
- Input Power Factor and (optional) Ambient Temperature.
- Choose NEC or IEC standard.
- Click Calculate.
- Instantly see: Voltage drop (volts), percentage drop, load voltage at end of run, corrected resistance, compliance status (lighting ≤3%, power ≤5%), step-by-step audit trail, safety recommendations, and live visualizations.
- Export CSV for your project documentation.
Examples
Example 1 – NEC Single-Phase Lighting Circuit (Long Run) Voltage: 120 V 1-Phase, Load Current: 15 A, Length: 450 ft (137 m), Copper 12 AWG, PF=1.0, Ambient 35°C Results: Voltage Drop = 4.8 V (4.0%), Load Voltage = 115.2 V, Corrected Resistance = 9.12 Ω/km → COMPLIANCE WARNING (exceeds 3% lighting limit). Recommendation: Upsize to 10 AWG.
Example 2 – IEC Three-Phase Motor Feeder Voltage: 400 V 3-Phase, Load Current: 120 A, Length: 800 m, Aluminum 150 mm², PF=0.85, Ambient 45°C Results: Voltage Drop = 18.7 V (4.7%), Load Voltage = 381.3 V, Compliance PASS (within 5% power limit).
Voltage Drop Categories / Normal Range
| Circuit Type | Max Allowed % Drop (NEC/IEC) | Typical Acceptable Range | Common Conductor Sizes (Copper) |
|---|---|---|---|
| Lighting & Sensitive Loads | ≤3% | 1–2.5% | 14–10 AWG |
| General Power Receptacles | ≤5% | 2–4% | 12–6 AWG |
| Motor Feeders | ≤5% (recommended ≤3%) | 2–4.5% | 4/0–500 kcmil |
| Long Industrial Runs | ≤5% | 3–5% | 350–1000 kcmil |
| PV / Solar DC Runs | ≤2–3% (best practice) | 1–2% | 10–4 AWG |
Limitations
- Uses DC resistance values at 20°C (NEC Table 8); does not model AC skin effect or reactance for very large conductors.
- Voltage drop assumes steady-state load and uniform temperature; actual drop may vary with load profile or harmonics.
- Does not calculate short-circuit current, ground-fault protection, or arc-flash energy.
- Aluminum terminations require special lugs and compound not modeled here.
- Results are for preliminary design; final sizing must be verified by a licensed electrical engineer and local AHJ.
Disclaimer
This Voltage Drop Calculator is a decision-support tool based on NEC Chapter 9 Table 8 and IEC standards. It does not replace professional electrical engineering judgment, site-specific calculations, or authority having jurisdiction (AHJ) approval. All installations must comply with the latest edition of the applicable electrical code and be performed by qualified personnel. Incorrect conductor sizing can result in equipment malfunction, overheating, fire, or personal injury. The developers and platform accept no liability for any errors, financial loss, or safety incidents arising from use of this tool.