3TM Voltage Drop Calculator
Advanced conductor sizing and voltage drop analysis for DC, single-phase and three-phase circuits.
01. Electrical System
02. Conductor Parameters
03. Engineering Results
| Parameter | Value | Unit / Notes |
|---|
Calculation Method
Single-phase AC and DC: voltage drop accounts for the outgoing and return path.
Three-phase AC: voltage drop uses the three-phase line-to-line relationship.
For AC, the simplified model uses conductor resistance, entered reactance and power factor. This is an engineering estimate, not a complete circuit simulation.
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| Southwire voltage drop calculator |
3TM Voltage Drop Calculator – Advanced Wire Size, Voltage Loss & Circuit Analysis
The 3TM Voltage Drop Calculator helps electricians, contractors, engineers, and DIY users estimate voltage drop in electrical circuits. It supports single-phase AC, three-phase AC, and DC calculations, with options for copper and aluminum conductors, wire sizes from AWG to kcmil, conductor temperature, power factor, and reactance.
Use this calculator to estimate voltage loss, receiving voltage, percentage voltage drop, conductor power loss, and a suitable wire size based on your selected voltage-drop limit.
What Is a Voltage Drop Calculator?
A voltage drop calculator estimates how much electrical voltage is lost as current travels through a conductor. Every wire has resistance, so voltage at the load can be lower than voltage at the power source.
Excessive voltage drop can affect equipment performance, motor starting, lighting, and electrical efficiency. Selecting an appropriate conductor size helps reduce voltage loss and improve circuit performance.
Key Features of the 3TM Voltage Drop Calculator
- Multiple circuit types: Calculate single-phase AC, three-phase AC, and DC voltage drop.
- Copper and aluminum conductors: Choose the conductor material for your calculation.
- AWG and kcmil wire sizes: Compare commonly used conductor sizes.
- Custom conductor resistance: Enter a resistance value when using verified conductor data.
- Conductor temperature adjustment: Estimate how resistance changes with temperature.
- Power factor and reactance: Include these inputs for a more representative AC estimate.
- Voltage drop percentage: See voltage loss in volts and as a percentage of source voltage.
- Receiving voltage: Estimate the voltage available at the load.
- Conductor power loss: View an approximate resistive power-loss estimate.
- Suggested wire size: Find a listed wire size that meets the selected voltage-drop target under the calculator’s assumptions.
- CSV export and printing: Save calculation results or print them for reference.
How to Use the Voltage Drop Calculator
- Select the circuit type: single-phase AC, three-phase AC, or DC.
- Enter the source voltage and circuit current in amperes.
- Enter the one-way conductor length and select feet or meters.
- Choose copper or aluminum and select the conductor size.
- Enter the conductor temperature and, for AC circuits, the power factor and reactance when applicable.
- Set your maximum acceptable voltage-drop percentage.
- Click Calculate Voltage Drop to view the estimated voltage loss, percentage drop, receiving voltage, and conductor power loss.
- Use Find Suggested Wire Size to identify a listed conductor size that meets the selected voltage-drop target.
- Export the results to CSV or use the print option to save a PDF.
Always use the correct one-way distance, conductor data, and circuit configuration. The calculator accounts for the return path in its simplified DC and single-phase calculations.
Voltage Drop Calculation Formula
The calculation method depends on the type of circuit.
DC Circuits
A simplified DC voltage-drop formula is:
Voltage Drop = 2 × Current × One-Way Length × Resistance
When length is in feet and resistance is in ohms per 1,000 feet:
VD = 2 × I × L × R / 1000
Where:
- VD = voltage drop in volts
- I = circuit current in amperes
- L = one-way conductor length in feet
- R = conductor resistance in ohms per 1,000 feet
The factor of 2 accounts for the outgoing and return conductors in a typical two-wire DC circuit.
Single-Phase AC Circuits
A simplified AC calculation can include both conductor resistance and reactance:
VD ≈ 2 × I × L × (R × PF + X × sin θ) / 1000
Here, PF is the power factor, θ is the angle whose cosine equals PF, R is resistance, and X is reactance per 1,000 feet.
Three-Phase AC Circuits
For a balanced three-phase circuit, the calculator uses this approximate relationship:
VD ≈ √3 × I × L × (R × PF + X × sin θ) / 1000
These are simplified engineering estimates. Actual voltage drop can vary with conductor temperature, conductor construction, installation conditions, and the electrical characteristics of the circuit.
Example: Voltage Drop Calculation
Consider a simplified DC circuit with the following values:
| Parameter | Example value |
|---|---|
| Source voltage | 120 V |
| Current | 20 A |
| One-way length | 100 ft |
| Conductor resistance | 1.0 Ω per 1,000 ft |
Using the DC formula:
VD = 2 × 20 × 100 × 1.0 / 1000
Estimated voltage drop: 4 V
Voltage-drop percentage:
(4 / 120) × 100 = 3.33%
Estimated receiving voltage:
120 − 4 = 116 V
This example illustrates the formula only. Use the actual resistance for the selected conductor and operating temperature for a practical calculation.
Why Is Voltage Drop Important?
Voltage drop matters because electrical equipment is designed to operate within a specified voltage range. Excessive loss along a circuit may contribute to dim lighting, reduced equipment performance, motor-starting problems, and wasted electrical energy.
Longer circuits, higher current, and smaller conductors generally increase voltage drop. Larger conductors usually reduce resistance and therefore reduce voltage loss, although the final conductor choice must also meet ampacity and installation requirements.
Voltage Drop vs. Ampacity
Voltage drop and ampacity are different electrical considerations.
| Comparison | Voltage drop | Ampacity |
|---|---|---|
| Meaning | Voltage lost along the conductor | Current a conductor can safely carry under specified conditions |
| Main factors | Length, current, resistance, circuit type, and AC power factor/reactance | Conductor material, insulation rating, installation conditions, ambient temperature, and adjustment factors |
| Main purpose | Evaluate voltage delivered to the load | Protect conductors against excessive heating |
| Can one replace the other? | No | No |
A conductor that meets a voltage-drop target may still be too small for the circuit’s required ampacity. Check both independently.
Common Voltage Drop Questions
1. What is an acceptable voltage drop?
A commonly used design guideline is around 3% for a branch circuit and 5% combined for feeder and branch circuits. These figures are design recommendations in common electrical guidance, not universal limits for every circuit. Check the applicable code, project specifications, and equipment requirements.
2. Does wire length affect voltage drop?
Yes. As conductor length increases, resistance increases, so voltage drop generally increases when other conditions remain the same. For two-wire DC and single-phase circuits, the return path must also be considered.
3. Which conductor has less voltage drop, copper or aluminum?
For comparable conductor sizes and conditions, copper generally has lower resistance than aluminum. Aluminum conductors may require a larger size to achieve a similar voltage-drop result.
4. Can this calculator recommend a wire size?
Yes. The suggested-size feature identifies a listed conductor size that meets the selected voltage-drop target under the calculator’s assumptions. The result is not a complete conductor-sizing decision; ampacity, protection, terminal ratings, and applicable code requirements must also be checked.
5. Does the calculator support three-phase circuits?
Yes. Select three-phase AC and enter the circuit voltage, current, conductor length, power factor, and applicable reactance information.
6. What is the difference between voltage drop in volts and percentage?
Voltage drop in volts shows the estimated numerical loss. Percentage voltage drop expresses that loss relative to the source voltage, making it easier to compare circuits operating at different voltages.
7. Does conductor temperature affect voltage drop?
Yes. Conductor resistance generally increases as temperature rises. The calculator’s temperature adjustment is an estimate, so use verified manufacturer or engineering data where accuracy is important.
8. Is this an official Southwire calculator?
No. The 3TM Voltage Drop Calculator is an independent calculation tool. It is not an official Southwire product and is not affiliated with or endorsed by Southwire.
9. Can I use the results for electrical installations?
Use the results as an estimate for planning and comparison. Before installation, verify conductor ampacity, overcurrent protection, insulation and terminal temperature ratings, applicable electrical codes, and the manufacturer’s conductor data. Consult a qualified electrical professional when required.
10. Can I save or print the results?
Yes. Use the CSV export option to save the calculation data, or use the print option in your browser to print or save the results as a PDF.
Important Electrical Disclaimer
This calculator provides estimates for educational, planning, and preliminary design purposes. Conductor resistance values and temperature adjustments may be approximate, and simplified AC calculations may not represent every installation. The suggested wire size is based on voltage drop only; it does not establish code compliance or replace ampacity calculations, engineering review, or manufacturer specifications.
Southwire Voltage Drop Calculator – Wire Size & Voltage Loss
The 3TM Voltage Drop Calculator provides a practical way to compare conductor sizes and estimate voltage loss across DC, single-phase AC, and three-phase AC circuits. With support for conductor material, temperature, power factor, reactance, and suggested wire sizing, it offers more flexibility than a basic voltage-drop calculator.
Use the results alongside applicable electrical codes and verified conductor specifications to make informed wiring decisions.
