Cable Voltage Drop Calculator
Accurate voltage drop calculations for DC, Single-phase & Three-phase systems compliant with IEC, IEEE & NEC standards.
Voltage Drop Calculator
Select your standard and system parameters below
Calculation Results:
Voltage Drop (Vd): 0.00 V
Percentage Drop (%Vd): 0.00 %
How to use cable voltage drop calculator
1. Select Standard
Choose your compliance standard: IEC, IEEE, or NEC. This helps in visual compliance checks.
2. Enter System Details
Select your system Type (DC/AC), input the Voltage and Current of your load.
3. Cable Parameters
Input the cable Length and select the Unit (m/ft). Choose the Material (Copper/Aluminum).
4. Check & Calculate
Select a Cable Size and click Calculate. View the results and pass/fail status instantly.
How to Calculate Cable Voltage Drop As Per IEC, IEEE and NEC Standards
IEC & IEEE Standards
According to IEC 60364-5-52 and IEEE standards, the recommended voltage drop limits are crucial for safety and efficiency:
Maximum Voltage Drop = 3% (Branch Circuits)
Maximum Voltage Drop = 5% (Total System)
These limits prevent equipment overheating and ensure proper operation of sensitive electronics.
NEC Recommendation
The National Electrical Code (NEC) provides an Informational Note (not a mandatory rule) suggesting similar efficiency levels:
NEC 210.19(A) Note 4: Max 3% for Branch Circuits
Total Combined Drop: Max 5% (Feeder + Branch)
Adhering to these recommendations ensures your electrical installation meets industry best practices.
Calculation Formula
The universal formula for calculating voltage drop depends on the system type (DC vs AC) and phases:
Vd = (K × I × L × R) ÷ 1000
Where:
I: Load Current (Amps)
L: Length (m)
R: Resistance (Ω/km)
K = 2 (DC/1-Phase), √3 (3-Phase)
Real-Life Industrial Example
1. The Scenario
You need to power a 100A industrial motor using a 35mm² copper cable over a distance of 100 meters.
- Supply: 415V 3-Phase AC
- PF: 0.85
- Length: 100m
2. The Calculation
Identify resistance and apply the standard formula.
Use parameters:
- R ≈ 0.627 Ω/km (35mm² Cu)
- K = 1.732 (√3 for 3-Phase)
Vd = (1.732 × 100 × 100 × 0.627 × 0.85) ÷ 1000
Vd = 9.23 Volts
3. Compliance
Verify if the drop is within the 3% limit.
Cable Voltage Drop Chart
| Cable Size (mm²) | Approx. Voltage Drop (mV/A/m) - 1 Phase | Approx. Voltage Drop (mV/A/m) - 3 Phase |
|---|---|---|
| 1.5 mm² | 29.0 | 25.0 |
| 2.5 mm² | 18.0 | 15.0 |
| 4.0 mm² | 11.0 | 9.5 |
| 6.0 mm² | 7.3 | 6.3 |
| 10.0 mm² | 4.4 | 3.8 |
| 16.0 mm² | 2.8 | 2.4 |
| 25.0 mm² | 1.75 | 1.50 |
| 35.0 mm² | 1.25 | 1.10 |
Cable Voltage Drop FAQs
How do you calculate the voltage drop of a cable?
To calculate voltage drop, multiply current (Amps) by distance (Length) and the cable's resistance per unit length. Then apply the system factor (2 for DC/Single-phase, 1.732 for Three-phase). The formula is Vd = (K × I × L × R) / 1000.
What is the 3% voltage drop rule?
The 3% rule is a widely accepted recommendation (NEC 210.19 Note 4) stating that the maximum voltage drop for branch circuits (from the final distribution board to the device) should not exceed 3% of the supply voltage to ensure efficiency.
What is the voltage drop for 100 feet?
Voltage drop for 100 feet depends entirely on the current (Load) and cable thickness (AWG). For example, 20 Amps flowing through #12 AWG copper wire at 120V over 100 ft will drop approximately 6.6 Volts (5.5%).
What is the voltage drop on a 3 phase cable?
In a 3-phase system, voltage drop is calculated using √3 (1.732) as the multiplier instead of 2. It is generally lower for the same load and distance compared to a single-phase system due to the efficiency of three-phase power transmission.
Is a 5% voltage drop ok?
Yes, a 5% total voltage drop constitutes the maximum recommended limit for the combined feeder and branch circuit lengths. If the drop exceeds 5%, it may cause motors to overheat or lights to dim significantly.
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