Voltage Drop Calculator
Free AS/NZS 3008 compliant voltage drop calculator for Australian electrical installations
Free Voltage Drop Calculator
Enter your circuit parameters below to calculate voltage drop based on AS/NZS 3008.
This is a simplified calculation. For detailed analysis with all derating factors and compliance checking, use our professional calculator.
Get Full Calculation ReportHow to Use This Voltage Drop Calculator
Enter the load current, cable length, system voltage, cable size and conductor material above. The calculator applies the AS/NZS 3008 mV/A/m value for the cable and reports the voltage drop in volts and as a percentage of system voltage, with a compliance status against the AS/NZS 3000 limits.
What is Voltage Drop?
- Equipment malfunction: Motors may not start, or may run hot and inefficiently
- Reduced light output: Lighting may appear dim or flicker
- Increased energy consumption: Equipment draws more current to compensate
- Overheating: Cables may overheat if undersized for the actual current draw
- Non-compliance: Installations may not meet AS/NZS 3000 requirements
Key Point: Voltage drop is calculated using mV/A/m values from AS/NZS 3008 tables. The formula considers current, cable length, phase configuration, and cable characteristics.
The Voltage Drop Formula
Single-phase: VD = (I × L × 2 × mV/A/m) / 1000Three-phase: VD = (I × L × √3 × mV/A/m) / 1000Percentage: VD% = (VD / System Voltage) × 100
Factors Affecting Voltage Drop
Cable Length
Voltage drop is directly proportional to length: doubling the run doubles the drop.
Current Magnitude
Higher currents produce proportionally higher voltage drop through the same cable.
Cable Size
Larger cross-sectional areas have lower impedance and therefore lower mV/A/m values.
Conductor Material
Copper has about 1.6 times the conductivity of aluminium, so aluminium cables of the same size drop more voltage.
Temperature
Conductor resistance rises with temperature, so hot cables drop slightly more voltage than the tabulated values suggest.
AS/NZS 3000 Voltage Drop Requirements
- Consumer mains: Maximum 2% voltage drop from point of supply to the main switchboard
- Submains and final subcircuits: Maximum 5% total from point of supply to any outlet
- Motor circuits: May need additional consideration for starting currents
How to Reduce Voltage Drop
- Increase cable size - the most common fix, lowering the mV/A/m value
- Shorten cable runs - relocate distribution boards closer to loads
- Use copper instead of aluminium - better conductivity for the same size
- Increase system voltage - three-phase supply reduces current for the same power
- Split loads - run separate circuits so each carries less current
- Use parallel cables - halves the effective impedance on large feeders
Cable mV/A/m Values Reference
Use these values for voltage drop calculations. Based on AS/NZS 3008.1.1 for cables enclosed in conduit at 50Hz.
| Size (mm²) | mV/A/m (0.8 PF) |
|---|---|
| 1.5 | 29 |
| 2.5 | 18 |
| 4 | 11 |
| 6 | 7.3 |
| 10 | 4.4 |
| 16 | 2.8 |
| 25 | 1.8 |
| 35 | 1.3 |
| 50 | 0.93 |
| 70 | 0.63 |
| 95 | 0.46 |
| 120 | 0.36 |
| Size (mm²) | mV/A/m (0.8 PF) |
|---|---|
| 16 | 4.6 |
| 25 | 2.9 |
| 35 | 2.1 |
| 50 | 1.55 |
| 70 | 1.1 |
| 95 | 0.78 |
| 120 | 0.61 |
Aluminium conductors are typically only used for sizes 16mm² and above.
| Circuit Type | Maximum Voltage Drop | Notes |
|---|---|---|
| Consumer mains | 2% | From point of supply to main switchboard |
| Submains | 5% total | Combined with consumer mains |
| Final subcircuits | 5% total | From point of supply to any outlet |
| Motor circuits | 5% running / 3% starting | Starting voltage drop may need separate assessment |
Important: These are maximum limits. Best practice is to keep voltage drop below 3% where possible for optimal equipment performance.
Professional Features
Why Use CableHero's Full Calculator?
Our professional cable sizing software provides comprehensive voltage drop analysis with complete AS/NZS 3008 compliance.
Complete Voltage Analysis
- Accurate mV/A/m for every cable
- Single & three-phase
- Power factor considered
- Compliance indicators
All Derating Factors
- Temperature (Table 27)
- Grouping (Table 22)
- Burial depth (Table 28)
- Soil resistivity (Table 29)
Automatic Cable Sizing
- Smallest compliant size
- Current capacity check
- Voltage drop check
- Fault loop impedance
PDF Reports
- Professional format
- Full calculation breakdown
- Certification ready
- Custom branding
Complete Cable Database
- Copper & Aluminium
- PVC, XLPE, EPR
- All installation methods
- Manufacturer data
Project Management
- Save calculations
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Frequently Asked Questions
Voltage Drop Questions Answered
What is voltage drop?⌄
Voltage drop is the reduction in voltage along a cable as current flows through its resistance and reactance. Every conductor has some impedance, so the voltage at the load end is always lower than at the supply end. Excessive voltage drop causes equipment to malfunction, lights to dim and motors to run hot.
What is the maximum allowable voltage drop in Australia?⌄
AS/NZS 3000 limits the total voltage drop from the point of supply to any point in the installation to 5%. Consumer mains are typically limited to 2%, leaving 3% for submains and final subcircuits. Best practice is to keep voltage drop below 3% where possible.
How do I calculate voltage drop?⌄
Voltage drop = (I × L × K × mV/A/m) / 1000, where I is the current in amps, L is the route length in metres, K is 2 for single-phase or √3 for three-phase, and mV/A/m is the cable's voltage drop value from AS/NZS 3008. Divide by the system voltage and multiply by 100 for the percentage.
What factors affect voltage drop?⌄
Cable length, current magnitude, cable size (cross-sectional area), conductor material (copper vs aluminium) and conductor temperature all affect voltage drop. Longer runs, higher currents, smaller cables, aluminium conductors and higher temperatures all increase voltage drop.
How do I reduce voltage drop?⌄
Increase the cable size, shorten the cable run, use copper instead of aluminium, increase the system voltage (e.g. three-phase instead of single-phase), split the load across more circuits, or run cables in parallel.
What is mV/A/m and where do I find the values?⌄
mV/A/m is the millivolts of voltage drop per amp of current per metre of cable, as tabulated in AS/NZS 3008.1.1 for each cable size, conductor material, insulation and installation method. The reference table on this page lists common values for cables in conduit at 50Hz.
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