Calculate voltage rise for solar PV, generators, and regenerative loads per AS/NZS 3008
Enter your export parameters below to calculate voltage rise for generators, solar PV, or other power-exporting equipment based on AS/NZS 3008.
Voltage rise is a phenomenon that occurs when electrical current flows in the opposite direction to normal power flow. While most electricians are familiar with voltage drop (where voltage decreases from supply to load), voltage rise is equally important to understand, especially with the increasing prevalence of solar PV systems, generators, and regenerative equipment.
In a typical electrical installation, power flows from the supply (grid) to the loads (equipment). This causes a voltage drop along the cable due to the cable's resistance and reactance. However, when power flows in the opposite direction - from a local source back towards the grid - the voltage actually increases along the cable.
This increase in voltage is called voltage rise, and it occurs at the point where the power is being generated or exported. The voltage at the generator, solar inverter, or other export point will be higher than the voltage at the grid connection point.
Key Point: Voltage rise uses the same calculation formula as voltage drop, but the effect is reversed. Instead of voltage decreasing from supply to load, it increases from the export source toward the grid connection.
Understanding the relationship between voltage rise and drop is essential for proper system design:
Voltage rise is a consideration in several common scenarios:
The most common cause of voltage rise in modern installations. During peak generation (typically midday), solar PV systems export power to the grid, causing voltage rise along the connection cable. This is particularly significant for:
Backup generators and grid-connected generating sets export power during operation, causing voltage rise between the generator and the point of common coupling (PCC).
Variable speed drives used on lifts, cranes, hoists, and conveyors can return energy to the supply during braking or lowering operations. This regenerated energy causes voltage rise in the supply cables.
When batteries discharge and export power to the grid or to local loads, voltage rise occurs along the connection cables.
Voltage rise is calculated using the same approach as voltage drop, using the mV/A/m (millivolts per amp per meter) values from AS/NZS 3008:
Single-phase: VR = (I × L × 2 × mV/A/m) / 1000
Three-phase: VR = (I × L × √3 × mV/A/m) / 1000
Percentage: VR% = (VR / System Voltage) × 100
Where: I = export current (A), L = cable length (m), mV/A/m = cable impedance from AS/NZS 3008
The Australian/New Zealand wiring rules (AS/NZS 3000) specify that the combined voltage drop and voltage rise from the point of supply to any point in the installation should not exceed 5% under normal service conditions.
Important considerations:
Voltage Limits (AS/NZS 3000)
Combined rise + drop: 5%
Consumer mains: 2%
Common Voltage Rise Causes
Solar PV export
Generator operation
Regenerative drives
Battery discharge
Solutions for High Voltage Rise
Increase cable size
Shorten cable runs
Use copper instead of aluminium
Limit export current
Use these values for voltage rise (and 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 |
| Circuit Type | Maximum Voltage Variation | 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 |
| Solar PV installations | 5% combined | Rise during export + drop during import |
Professional Features
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Frequently Asked Questions
Voltage rise occurs when current flows in the opposite direction to normal power flow, causing the voltage at the source end to be higher than at the supply point. This commonly happens with generators feeding into the grid, solar PV systems during peak generation, regenerative drives returning energy, and battery systems during discharge. Unlike voltage drop where voltage decreases along the cable, voltage rise increases voltage along the cable in the direction of power flow.
Voltage drop occurs when power flows from the supply to the load, causing voltage to decrease along the cable. Voltage rise is the opposite - when power flows from a local source (like solar PV or a generator) back towards the supply, voltage increases along the cable. Both use the same calculation formula and mV/A/m values from AS/NZS 3008, but the direction of the voltage change is reversed. In practice, you need to consider both: voltage drop during import and voltage rise during export.
Common causes include: Solar PV systems exporting power during peak generation periods, Generators feeding power into the grid or local network, Regenerative drives on lifts, cranes, or conveyors returning energy during braking, Battery storage systems during discharge mode, and Capacitor banks creating leading power factor. In all cases, current flowing towards the supply creates a voltage rise proportional to the cable impedance.
According to AS/NZS 3000, the combined voltage rise and voltage drop from the point of supply to any point in the installation should not exceed 5% under normal conditions. This means if your installation has 2% voltage drop during normal loads, only 3% remains available for voltage rise during export. Network operators (DNSPs) may impose additional limits at the point of connection, typically around 2% voltage rise.
Voltage rise uses the same formula as voltage drop. For single-phase: VR = (I × L × 2 × mV/A/m) / 1000. For three-phase: VR = (I × L × √3 × mV/A/m) / 1000. Where I is the export current in amps, L is the cable length in meters, and mV/A/m is the cable impedance value from AS/NZS 3008 tables. The percentage voltage rise is: VR% = (VR / System Voltage) × 100. Use our calculator above for quick calculations.
You should consider voltage rise when designing: Solar PV systems - especially larger commercial installations, Generator connections that will export to the grid, Regenerative drives for lifts, hoists, or conveyors, Battery storage systems with grid export capability, and any installation where power will flow back towards the supply. Voltage rise becomes more critical with longer cable runs, higher export currents, and installations at the end of distribution feeders.
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