AC and DC Voltage Drop Calculator AS/NZS 3008

Calculate the AC or DC voltage drop with this Free Online Voltage Drop Calculator. Supports AS/NZS 3008. Includes voltage drop Formulas and Examples.

Choose what to calculate

Voltage (V)

Load rating (A, hp, kW or kVA)

Cable size (mm2)

Voltage Drop Calculator Parameters

• Choose what to calculate: Voltage drop, Minimum cable size or Maximum cable distance
• Rated voltage (V): Specify the voltage in volt, and select the phase arrangement: 1 Phase AC, 3 Phase AC or DC.
• Load (kW, kVA, A, hp): Specify the load in A, hp, kW or kVA. Specify the power factor (cosΦ) when the electrical load is specified in kW or hp.
• Cable size (mm2): Select a standard electrical cable size in mm2, as defined in the AS/NZS 3008.
• Distance (m, ft): Specify the estimated cable length in meters or feet.
• Allowable voltage drop (%): Specify the maximum allowable voltage drop in a percentage of the nominal voltage. What is allowed? Click here for more information.

What is Voltage Drop?

Voltage drop is the loss of voltage over a wire due to the wire's electrical resistance and reactance. The problem with voltage drop is:

• It may cause equipment to malfunction.
• It reduces the potential energy.
• It results in an energy loss.

For example, if you supply a 21 Ω heater from a 230 V supply. And the resistance of the wire is 1 Ω. Then the current will be I = 230 V / (21 Ω + 2 × 1 Ω) = 10 A.

The voltage drop will be Vdrop = 10 A × 2 × 1 Ω = 20 V. Therefore, only 210 V will be available for your appliance. And P = 20 V × 10 A = 200 W will be wasted as heat in the wire.

What is the Allowable Voltage Drop?

AS/NZS 3008 in Australia and New Zealand specifies the following values:

 Final sub-circuit only. 3% From the Point of Supply to the final load 5% From the LV terminals of a transformer to the final load 7%

In simple terms, the maximum total allowable voltage drop at a socket outlet is 7%.

For residential applications this means:

• The utility limits the voltage drop at the Point of Supply to 2%.
• You have to limit the voltage drop between the Point of Supply and the Main Switchboard (or any sub-distribution board) to 2%.
• And you have to limit the voltage drop in the final sub-circuit to 3%.

Therefore, 2% + 2% + 3% = 7 %.

Typical voltage drop applications are shown below:

 Residential and light commercial 5% AS/NZS 3000:2007. Between the Point of Supply and load. Industrial and large commercial 7% AS/NZS 3000:2007. Between the Point of Supply and load. Where the Point of Supply is the low voltage terminals of a transformer. Industrial 3% Common practice. Between switchboard and continuous loads, e.g. motors. Where the transformer and switchboard is part of the installation (site). Industrial 5% Common practice. Between switchboard and intermittent loads, e.g. valves. Where the transformer and switchboard is part of the installation (site).

How to Calculate Voltage Drop?

The voltage drop formulas for AC and DC are shown in the table below.

 1-phase AC $$\Delta V_{1\phi-ac}=\dfrac{I L 2 Z_c}{1000}$$ 3-phase AC $$\Delta V_{3\phi-ac}=\dfrac{I L \sqrt{3} Z_c}{1000}$$ DC $$\Delta V_{dc}=\dfrac{I L 2 R_c}{1000}$$

Where,

• I is the load current in ampere (A).
• L is the wire distance on meters (m).
• Zc is the wire impedance in Ω/km.
• Rc is the wire resistance in Ω/km.

The impedance Zc in the voltage drop calculator is calculated as:

$$Z_c = \sqrt{R_c^2 + X_c^2}$$

Where,
• Rc is the wire resistance in Ω/km.
• Xc is the wire reactance in Ω/km.

The formula above for Zc is for the worse case. This is when the cable and load power factor is the same.

The Volt Drop Calculator uses the AC resistance Rc values from Table 35 in AS/NZS 3008. The following column is used: 75°C, AC, multi-core, circular conductors.

Note that the standard does not specify the DC resistance.

The cable rating that is displayed in the results of the calculator is selected from Table 13 in AS/NZS 3008. This is for thermoplastic (PVC), three- and four-core cables, unenclosed and spaced from a surface. For more cable types, use the Cable sizing calculator AS/NZS3008.

Voltage Drop Calculation Examples

Example 1: Voltage drop calculation example for a residential 230 VAC, 15 A, single-phase load.

 Voltage 230 VAC, single-phase Load 15 A Distance 30 m Conductor size 8 mm2

The resistance and reactance values in AS/NZS 3008 for an 8 mm2 two-core cable are:

• Rc = 2.23 Ω/km, from Table 35 -Multi-core, circular at 75°C.
• Xc = 0.0906 Ω/km, from Table 30 -Multi-core, circular, PVC insulated.

The impedance is calculated as:

$$Z_c = \sqrt{R_c^2 + X_c^2}$$

$$Z_c = \sqrt{2.23^2 + 0.0906^2}$$

$$Z_c = 2.232 \,\Omega/km$$

The voltage drop is calculated as:

$$\Delta V_{1\phi-ac}=\dfrac{I L 2 Z_c}{1000}$$

$$\Delta V_{1\phi-ac}=\dfrac{15 \cdot 30 \cdot 2 \cdot 2.232}{1000}$$

$$\Delta V_{1\phi-ac}=2.01 \, V$$

The percentage voltage drop is calculated as:

$$\% V_{1\phi-ac}= \dfrac {2.01} {230} \cdot 100$$

$$\% V_{1\phi-ac}= 0.87 \, \%$$

Example 2: Voltage drop calculation example for a residential 230 VAC, 10A socket outlet.

 Voltage 230 VAC, 1-phase Load One 10 A socket Distance 20 m Conductor size 2.5 mm2

The maximum demand current according to AS 3000: 2007 Table C 1 for one 10 A socket in a room is 10 A.

You can also calculate this with the Maximum Demand Calculator with Examples AS/NZS 3000

The resistance and reactance values in AS/NZS 3008 for a 2.5 mm2 two-core cable are:

• Rc = 9.01 Ω/km, from Table 35 -Multi-core, circular at 75°C.
• Xc = 0.102 Ω/km, from Table 30 -Multi-core, circular, PVC insulated.

The impedance is calculated as:

$$Z_c = \sqrt{R_c^2 + X_c^2}$$

$$Z_c = \sqrt{9.01^2 + 0.102^2}$$

$$Z_c = 9.01 \,\Omega/km$$

The voltage drop is calculated as:

$$\Delta V_{1\phi-ac}=\dfrac{I L 2 Z_c}{1000}$$

$$\Delta V_{1\phi-ac}=\dfrac{10 \cdot 20 \cdot 2 \cdot 9.01}{1000}$$

$$\Delta V_{1\phi-ac}=3.61 \, V$$

The percentage voltage drop is calculated as:

$$\% V_{1\phi-ac}= \dfrac {3.61} {230} \cdot 100$$

$$\% V_{1\phi-ac}= 1.57 \, \%$$

Example 3: Voltage drop calculation example for a residential 230 VAC, swimming pool pump.

 Voltage 230 VAC, 1-phase Load 0.75 kW, 0.85 power factor Distance 40 m Conductor size 4 mm2

The resistance and reactance values in AS/NZS 3008 for a 4 mm2 two-core cable are:

• Rc = 5.61 Ω/km, from Table 35 -Multi-core, circular at 75°C.
• Xc = 0.102 Ω/km, from Table 30 -Multi-core, circular, PVC insulated.

The impedance is calculated as:

$$Z_c = \sqrt{R_c^2 + X_c^2}$$

$$Z_c = \sqrt{5.61^2 + 0.102^2}$$

$$Z_c = 5.61 \,\Omega/km$$

The current is calculated as:

$$I = \dfrac{750}{230 \times 0.85} = \text{3.84 A}$$

The voltage drop is calculated as:

$$\Delta V_{1\phi-ac}=\dfrac{I L 2 Z_c}{1000}$$

$$\Delta V_{1\phi-ac}=\dfrac{3.84 \cdot 40 \cdot 2 \cdot 5.61}{1000}$$

$$\Delta V_{1\phi-ac}=1.72 \, V$$

The percentage voltage drop is calculated as:

$$\% V_{1\phi-ac}= \dfrac {1.72} {230} \cdot 100$$

$$\% V_{1\phi-ac}= 0.75 \, \%$$

Example 4: Voltage drop calculation example for an industrial 400 VAC, 3-phase motor.

 Voltage 400 VAC, 3-phase Load 22 kW motor, pf 0.86. Efficiency ignored.Full load current: 36.92 A Distance 100 m Conductor size 16 mm2

The resistance and reactance values in AS/NZS 3008 for a 16 mm2 two-core cable are:

• Rc = 1.4 Ω/km, from Table 35 -Multi-core, circular at 75°C.
• Xc = 0.0861 Ω/km, from Table 30 -Multi-core, circular, PVC insulated.

The impedance is calculated as:

$$Z_c = \sqrt{R_c^2 + X_c^2}$$

$$Z_c = \sqrt{1.4^2 + 0.0861^2}$$

$$Z_c = 1.403 \,\Omega/km$$

The voltage drop is calculated as:

$$\Delta V_{3\phi-ac}=\dfrac{I L \sqrt{3} Z_c}{1000}$$

$$\Delta V_{3\phi-ac}=\dfrac{36.92 \cdot 100 \cdot \sqrt{3} \cdot 1.403}{1000}$$

$$\Delta V_{3\phi-ac}=8.97 V \, V$$

The percentage voltage drop is calculated as:

$$\% V_{3\phi-ac}= \dfrac {10.2} {400} \cdot 100$$

$$\% V_{3\phi-ac}= 2.24 \, \%$$

Example 5: Voltage drop calculation example for a 12 VDC, 1 A load.

 Voltage 12 VDC Load 1 A Distance 30 m Conductor size 4 mm2

The resistance AS/NZS 3008 for a 4 mm2 two-core cable is:

• Rc = 5.61 Ω/km, from Table 35 -Multi-core, circular at 75°C.

Note that Reactance is not applicable in DC circuits.

Also note that there is no specific table in AS/NZS 3008 for DC resistance.

The voltage drop is calculated as:

$$\Delta V_{dc}=\dfrac{I L 2 R_c}{1000}$$

$$\Delta V_{dc}=\dfrac{1 \cdot 30 \cdot 2 \cdot 5.61}{1000}$$

$$\Delta V_{dc}=0.34 \, V$$

The percentage voltage drop is calculated as:

$$\% V_{dc}= \dfrac {0.34} {12} \cdot 100$$

$$\% V_{dc}= 2.83 \, \%$$