Voltage Rise Calculator Australia

Calculate voltage rise for solar PV, generators, and regenerative loads per AS/NZS 3008.1.1:2025

How to use

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Electrical Load

Unit

Load

Amps

Power factor

Cable

Cable core

Conductor type

Insulation type

System Supply

Supply

Length of run

Voltage

Voltage rise threshold

Standard limit

Inverter terminals to the main switchboard, or to the point of supply without high-export-voltage protection. (AS/NZS 4777.1; AS/NZS 3008.1.1:2025 Cl. 4.1.2)

Fault level

Fault time

Installation Method

Derating Factor

Assistant

Overall derating factor

Ambient for operating temperature

Reference ambient per AS/NZS 3008.1.1:2025 (40 °C in air).

Protection

Enabled

Enable to check the fault loop impedance against a protective device.

Cable Size

ActiveManual–Circuits in parallel–

NeutralManual–Circuits in parallel–

EarthManual–Circuits in parallel1

Spare capacity– A

Operating temperature– °C

Voltage rise– V (–%)

Three-phase SCC– A

Live to earth SCC– A

Fault loop impedance– Ω

Cable derated current1 A

Rated current– A

Cable resistance– Ω/km

Cable reactance– Ω/km

Min active conductor– mm²

Min earth conductor– mm²

Internal impedance– Ω

External impedance– Ω

How it's calculated

The AS/NZS 3008.1.1:2025 Method

The calculator above runs the full CableHero engine, the same one behind saved calculations and PDF reports. These are the checks it makes, with the numbers for the example it opens with.

1. Current-carrying capacity

AS/NZS 3008.1.1:2025 Clause 2.3.1, Section 3 tables; correction factors Clause 3.5

is the tabulated current-carrying capacity of the cable for its installation method (for example Table 3.15 for thermoplastic two-core cables), the design current and the product of the correction factors: grouping (Clause 3.5.2, Tables 3.33 to 3.43), air or soil temperature (Clause 3.5.3, Tables 3.44 and 3.45), depth of laying (Clause 3.5.4, Tables 3.46 and 3.47) and soil thermal resistivity (Clause 3.5.5, Table 3.48). The smallest size that passes, and then passes every check below, is selected.

2. Voltage rise

AS/NZS 3008.1.1:2025 Clauses 2.3.2, 4.3, 4.4 and 4.5

is the a.c. resistance at the conductor's operating temperature (Clause 4.4, read from Tables 4.1 to 4.13), the reactance, the load power factor and the route length in metres. is the three-phase value per Clause 4.3; a single-phase circuit has two conductors carrying the current, so its drop is times it (Clause 4.5). d.c. circuits use (Clause 4.7).

Voltage rise is the same calculation with the current flowing the other way, from an inverter, battery or generator back towards the supply. Grid-connected inverters are limited to 2% (AS/NZS 4777.1, as set out in AS/NZS 3008.1.1:2025 Clause 4.1.2), measured from the inverter terminals to the main switchboard, or to the point of supply without high-export-voltage protection.

3. Short circuit and fault loop

AS/NZS 3008.1.1:2025 Clause 5.3; AS/NZS 3000:2018 Clause 5.7.4 and Appendix B5.2.2

The active and earth conductors must withstand the prospective fault current for the clearing time ( from Table 5.1). is the resistance of the active and earth conductors over the route; dividing by 0.8 allows for the 20% of the loop impedance upstream of the circuit. must not exceed , where is the current that trips the device instantly (for example for a Type C circuit breaker), so the device clears an earth fault in time.

Worked example

Export of 21.7 A single phase at 230 V, 20 m of Thermoplastic (75 °C) copper multicore, enclosed wiring enclosure in air. Limit 2% rise.

6 mm²: .
at , , : .
. The 2% limit allows up to 30 m with this cable.
2.5 mm² earth: , ; with a protective device set, the calculator checks it against .

Selected: 6 mm², voltage rise 1.34%.

References

Current-carrying capacity: AS/NZS 3008.1.1:2025 Clause 2.3.1; Table 3.15
Voltage drop: AS/NZS 3008.1.1:2025 Clauses 2.3.2, 4.3, 4.4 and 4.5; Table 4.7(A) (Rc); Table 4.1(B) (Xc)
Short-circuit temperature: AS/NZS 3008.1.1:2025 Clauses 2.3.3 and 5.3; Table 5.1 (K); Table 5.2 (limit)
Earth conductor size: AS/NZS 3000:2018 Table 5.1

Understanding Voltage Rise in Electrical Installations

What is Voltage Rise?

When an installation exports power, current flows from the local source towards the point of supply. The cable impedance then raises the voltage at the source end above the grid voltage. Inverters and generators must stay within their overvoltage limits, so voltage rise is a design constraint in its own right.

Voltage Rise vs Voltage Drop

Voltage Drop: current flows from the supply to a load, lowering the voltage at the load
Voltage Rise: current flows from a source to the supply, raising the voltage at the source
Same Formula: both use the AS/NZS 3008.1.1:2025 mV/A.m method
Different Limits: drop is limited to 5% by AS/NZS 3000:2018; rise from grid-connected inverters to 2% by AS/NZS 4777.1

When Does Voltage Rise Occur?

Solar PV Systems

Large commercial solar installations
Long cable runs from inverter to the main switchboard
Installations at the end of long distribution feeders

Generators

Standby and prime generators exporting into the installation or the grid.

Regenerative Drives

Variable speed drives that return braking energy to the supply.

Battery Storage Systems

Batteries discharging into the installation or exporting to the grid.

The Voltage Rise Formula

Voltage Rise Limits

AS/NZS 3008.1.1:2025 Clause 4.1.2 sets out the AS/NZS 4777.1 limits for grid-connected inverter energy systems:

With protection against high export voltages: at most 2% of the nominal supply voltage from the inverter output terminals to the connection to the installation (typically the voltage-sensing terminals at the main switchboard)
Without that protection: at most 2% in total from the inverter output terminals to the point of supply
Check your distributor's connection requirements for additional limits

AS/NZS 3008.1.1:2025 Voltage Drop Values

Use these values for voltage rise calculations. Three-phase Vc in mV/A.m for thermoplastic (V-75) multicore cables with conductors at 75°C, worst-case power factor (Tables 4.17 and 4.22); single-phase is 1.155 times it (Clause 4.5).

Copper Conductors (mV/A.m)
Size (mm²)	Vc three-phase	Vc single-phase
1.5	28.6	33
2.5	15.6	18
4	9.71	11.2
6	6.49	7.49
10	3.86	4.46
16	2.43	2.81
25	1.54	1.78
35	1.11	1.28
50	0.827	0.955
70	0.581	0.671
95	0.428	0.494
120	0.348	0.402

Aluminium Conductors (mV/A.m)
Size (mm²)	Vc three-phase	Vc single-phase
16	4.04	4.66
25	2.54	2.93
35	1.84	2.12
50	1.36	1.57
70	0.947	1.09
95	0.69	0.797
120	0.551	0.636

Voltage Limits
Case	Limit	Where it comes from
Inverter with high export voltage protection: inverter terminals to the installation connection	2% rise	AS/NZS 4777.1, via AS/NZS 3008.1.1:2025 Clause 4.1.2
Inverter without that protection: inverter terminals to the point of supply	2% rise	AS/NZS 4777.1, via AS/NZS 3008.1.1:2025 Clause 4.1.2
Voltage drop, point of supply to any point	5% drop	AS/NZS 3000:2018 Clause 3.6.2

Important: Voltage rise and voltage drop are checked separately against their own limits. Check with your distributor for any additional connection requirements.

Frequently Asked Questions

Voltage Rise Questions Answered

What is voltage rise?

Voltage rise is the increase in voltage at the point where power is exported into the network, for example at a solar inverter or generator. When current flows from the source towards the grid, the impedance of the cable raises the voltage at the source end above the grid voltage.

How is voltage rise different from voltage drop?

They are the same physical effect in opposite directions. Voltage drop occurs when current flows from the supply to a load; voltage rise occurs when current flows from a local source back towards the supply. The same mV/A.m method applies, but the limits differ: voltage drop is limited by AS/NZS 3000:2018, while voltage rise from grid-connected inverters is limited by AS/NZS 4777.1.

What causes voltage rise in electrical installations?

Solar PV export, generator operation, regenerative drives feeding braking energy back, and battery storage discharging all push current towards the point of supply and cause voltage rise along the cables.

What is the maximum allowable voltage rise?

For grid-connected inverter energy systems such as solar PV and batteries, AS/NZS 4777.1 limits voltage rise to 2% of the nominal supply voltage (as set out in AS/NZS 3008.1.1:2025 Clause 4.1.2). Where the inverter has protection against high export voltages, the 2% is measured from the inverter output terminals to its connection to the installation, typically the voltage-sensing terminals at the main switchboard. Without that protection, it is the total rise from the inverter terminals to the point of supply. Distributors may set further connection requirements.

How do I calculate voltage rise?

Three-phase voltage rise = (Vc × I × L) / 1000, where Vc is the three-phase voltage drop in mV/A.m from AS/NZS 3008.1.1:2025, I is the export current and L is the cable length. For single-phase, multiply by 1.155 (2/√3, Clause 4.5). Divide by system voltage for the percentage.

When should I consider voltage rise in my design?

Any time the installation exports power: large commercial solar installations, long cable runs from the inverter to the main switchboard, installations at the end of long distribution feeders, standby generators and battery storage systems.

Reviewed by Ahmed Tayeh, electrical engineer at CableHero. The calculator is a design aid: the designer remains responsible for checking the installation against the standards.

Guides

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How to use this calculator

Size the AC cable from a solar inverter so the voltage rise stays inside the 2% limit.

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