How is capacitor bank size calculated for power factor correction?

The required capacitive reactive power is Qc = kW × (tanφ₁ − tanφ₂), where φ₁ is the existing power factor angle and φ₂ is the target. For a 100 kW load improving from 0.75 PF (tanφ = 0.882) to 0.95 PF (tanφ = 0.329), Qc = 100 × (0.882 − 0.329) ≈ 55 kVAR. The ElecAS calculator then rounds this up to the next standard bank size.

What target power factor should I aim for in Australia?

Most Australian distribution network tariffs apply a kVA demand charge or a power factor penalty below 0.90, and some commercial tariffs target 0.95. A practical target is 0.95 lagging — high enough to clear most penalties without over-correcting. Correcting close to unity or into leading power factor at light load can cause overvoltage and resonance, so the calculator caps the target at the existing power factor as a floor.

Where should the capacitor bank be installed?

To reduce network demand charges, install at the main switchboard (global correction) — this is the packaged PFC panel shown in the connection diagram, tapping the MSB busbar through its own CB and CT. To also cut internal cable losses and free up upstream capacity, install close to large inductive loads such as motors and transformers (local correction). Where significant harmonic-generating load exists (VFDs, large rectifiers), use detuned or harmonic-filtered banks to avoid resonance.

Why does the bank cable and breaker use a ×1.5 design current?

A capacitor bank draws more than its nominal current Ic in service: IEC 60831 allows capacitance up to +10% tolerance, sustained overvoltage up to ~10%, and harmonic currents add further loading. Standard practice is to size the bank feeder cable and protective device at about 1.5 × the nominal bank current. ElecAS computes Ic from the installed standard bank size, applies the ×1.5 uplift, and sizes the cable and CB on that design current to AS/NZS 3008.1.1.

How much will power factor correction reduce my demand?

Correcting power factor reduces apparent power (kVA) and line current for the same real power (kW). Moving 100 kW from 0.75 to 0.95 PF drops apparent power from 133.3 kVA to 105.3 kVA — a 21% reduction in kVA demand and line current. The ElecAS calculator shows the initial and target kVA, the kVA reduction and the line-current reduction percentage directly from the power triangle.

How do I calculate the required kVAR for power factor correction?

Qc = P × (tanφ₁ − tanφ₂) where P is the real power in kW, φ₁ is the original power factor angle and φ₂ is the target power factor angle. For a 100 kW load at cosφ = 0.75 corrected to cosφ = 0.95, Qc = 100 × (0.882 − 0.329) = 55.3 kVAR. The ElecAS calculator then rounds this up to the next standard capacitor bank size.

How do I find the capacitance in microfarads for a power factor correction bank?

For a delta-connected bank the per-phase capacitance is C = Qc / (3 × V² × 2πf), where Qc is the correction in VAR, V is the line voltage and f is the frequency. The ElecAS calculator reports this value in microfarads (µF) directly, so you can specify or check the capacitor step against a manufacturer rating.

What size cable and breaker does a capacitor bank need?

Size them on the bank design current, not the nominal current. The nominal bank current is Ic = (kVAR × 1000) / (√3 × V); standard practice uplifts this by about 1.5× to allow for the IEC 60831 capacitance tolerance, sustained overvoltage and harmonic loading. ElecAS applies the ×1.5 uplift and auto-sizes a compliant cable and breaker to AS/NZS 3008.1.1:2025 from that design current.

How much does power factor correction reduce demand and current?

Correcting power factor lowers the apparent power (kVA) and the line current for the same real power (kW). Moving 100 kW from 0.75 to 0.95 PF reduces apparent power from 133.3 kVA to 105.3 kVA — about a 21% reduction in kVA demand and line current. The ElecAS calculator shows the initial and target kVA, the kVA reduction and the line-current reduction percentage.

Can over-correction cause problems?

Yes. Over-correction at light load produces a leading power factor which can cause voltage rise, damage motors and trip generator-set protective relays. Avoid it by sizing the bank to a realistic target (around 0.95) rather than unity, and by using an automatic stepped bank that switches capacitor stages on and off as the load varies.

Where should a power factor correction bank be installed?

To reduce network demand charges, install at the main switchboard (global correction) — the packaged PFC panel shown in the connection diagram, tapping the MSB busbar through its own CB and CT. To also cut internal cable losses and free up upstream capacity, install close to large inductive loads such as motors and transformers (local correction).

ElecAS

Power Factor Correction Calculator — kVAR Capacitor Bank Sizing for Australia

Free, browser-based power factor correction (PFC) calculator built for Australian electrical engineers, designers, electricians and estimators. Enter the real power load in kW, the existing power factor and a target power factor, and the calculator returns the required capacitive reactive power Qc = kW × (tanφ₁ − tanφ₂) in kVAR, rounds it up to the next standard capacitor bank size, and works the result through the full power triangle — initial and target apparent power (kVA), reactive power (kVAR) and the kVA demand reduction. It also sizes the delta-connected bank itself: per-phase capacitance in microfarads from C = Qc / (3·V²·ω), the nominal bank current Ic, and the ×1.5 design current that allows for capacitor tolerance, sustained overvoltage and harmonic loading. From that design current it auto-sizes a compliant bank feeder cable and circuit breaker to AS/NZS 3008.1.1:2025 (copper, X-90 XLPE, unenclosed spaced from surface, 20 m run, 2.5% voltage drop) and draws a single-line connection diagram of a packaged PFC panel with an integral regulator tapping the main switchboard busbar through its own CB and CT. Supports single-phase and three-phase systems, any nominal voltage and 50 or 60 Hz, with a branded PDF report including the power triangle and a clause-by-clause calculation breakdown.

Why this page matters

Who this page is for

Electrical engineers, designers, electricians, estimators and facilities managers sizing fixed and automatic capacitor banks to improve power factor, reduce kVA demand charges and free up consumer mains capacity on commercial and industrial installations across Australia and New Zealand.

Relevant standards

AS/NZS 3000:2018 (Wiring Rules — power factor correction equipment and switchboard connection)
AS/NZS 3008.1.1:2025 (Cable Selection — used to size the capacitor bank feeder cable and protective device)
AS 60038 (Standard Voltages — 230 V / 400 V nominal envelope)
IEC 60831 (Shunt power capacitors — tolerance and overvoltage basis for the ×1.5 design current uplift)

What this tool helps with

Calculates the required capacitive reactive power Qc = kW × (tanφ₁ − tanφ₂) in kVAR to move from an existing power factor to a target power factor.
Rounds the required kVAR up to the next standard capacitor bank size from the common 1 – 600 kVAR ladder so the recommendation matches real switchable bank steps.
Sizes the delta-connected bank — per-phase capacitance in microfarads from C = Qc / (3·V²·2πf), the nominal bank current Ic, and the ×1.5 design current that covers capacitor tolerance, overvoltage and harmonic loading.
Auto-sizes a compliant bank feeder cable and circuit breaker on the ×1.5 design current to AS/NZS 3008.1.1:2025 (copper, X-90 XLPE, unenclosed spaced from surface, 20 m, 2.5% voltage drop) — a one-click estimate that hands off to the full Cable Selection tool for fault and earth-loop checks.
Draws a power triangle showing initial apparent power (S1), target apparent power (S2), both reactive components and the correction Qc, plus the kVA demand reduction and the line-current reduction percentage at the same active power.
Generates a single-line connection diagram of a packaged PFC panel with an integral PF controller/regulator, contactor and delta capacitor bank tapping the MSB busbar through its own CB and incomer CT.
Works for single-phase and three-phase systems at any nominal voltage and 50 or 60 Hz, and exports a branded PDF report with the power triangle and a step-by-step calculation breakdown.

How to size a power factor correction capacitor bank

Enter the real power load in kW — Enter the connected real power load in kilowatts. For a mixed load use the operating-time-weighted average real power from a kWh meter or measurement.
Set the current power factor — Drag the Current Power Factor slider to the measured existing power factor (cosφ), typically read from a power-quality meter or the utility bill. The slider covers 0.50 to 0.99.
Set the target power factor — Drag the Target Power Factor slider to the value you want to reach — usually 0.90 or 0.95 to clear a network power factor penalty. The target cannot be set below the current power factor.
Enter the system voltage and frequency — Enter the nominal line voltage (for example 400 V three-phase or 230 V single-phase) and the supply frequency (50 Hz in Australia, 60 Hz elsewhere). These drive the delta capacitance and bank current.
Read the required kVAR and standard bank size — The calculator shows the required correction Qc = kW × (tanφ₁ − tanφ₂) in kVAR and rounds it up to the next standard bank size, alongside the per-phase delta capacitance in µF, the nominal bank current Ic and the ×1.5 design current.
Check the auto-sized bank cable and export the PDF — Review the automatically sized AS/NZS 3008.1.1 bank feeder cable and breaker on the connection diagram, then export the branded PDF report with the power triangle and the full calculation breakdown.

Power factor correction capacitor bank sizing for Australian installations

Why power factor correction matters

A low power factor (cosφ below 0.90) means the installation draws more apparent power (kVA) than real power (kW), increasing the current in the consumer mains, the I²R losses, the voltage drop and the kVA capacity charged by the network operator. Most Australian distribution network tariffs apply a kVA demand charge or a power factor penalty when the monthly average drops below 0.90; some commercial tariffs require 0.95.

Power factor correction adds capacitive reactive power (kVAR) to offset the inductive kVAR drawn by motors, transformers and other reactive loads, bringing cosφ closer to unity. Correctly sized PFC reduces the kVA demand and the line current for the same real power output, and on most commercial sites pays for itself in 6–24 months.

The PFC sizing formula

The required capacitive reactive power is Qc = P × (tanφ₁ − tanφ₂) where P is the real power in kW, φ₁ is the original power factor angle and φ₂ is the target. For P = 100 kW, original cosφ = 0.75 (tanφ = 0.882), target cosφ = 0.95 (tanφ = 0.329), Qc = 100 × (0.882 − 0.329) = 55.3 kVAR.

The ElecAS calculator works this through the full power triangle. It reports the initial apparent power S1 = kW / cosφ₁ and reactive power Q1 = kW × tanφ₁, the target apparent power S2 = kW / cosφ₂ and reactive power Q2, the correction Qc = Q1 − Q2, and the resulting kVA demand reduction (S1 − S2) and line-current reduction percentage. The required kVAR is then rounded up to the next standard capacitor bank size from the common ladder (1, 2.5, 5, 7.5, 10 … 600 kVAR) so the recommendation matches a real switchable bank.

Delta capacitance, bank current and the design-current uplift

For a delta-connected bank the per-phase capacitance is C = Qc / (3 × V² × ω) where V is the line voltage and ω = 2πf. The calculator reports this in microfarads (µF) so the bank can be specified or checked against a manufacturer step rating. It also computes the nominal bank current Ic = (kVAR × 1000) / (√3 × V) from the installed standard bank size.

A capacitor bank draws more than its nominal current in service: IEC 60831 permits up to +10% capacitance tolerance and sustained overvoltage of about 10%, and harmonic currents add further loading. ElecAS therefore applies a ×1.5 uplift to Ic to give a design current, and sizes the bank feeder cable and circuit breaker on that figure — the standard approach for protecting and connecting a capacitor bank.

Automatic bank cable and breaker sizing to AS/NZS 3008.1.1

From the ×1.5 design current the calculator auto-sizes a compliant bank feeder cable and protective device to AS/NZS 3008.1.1:2025 using a fixed reference install — copper conductor, X-90 XLPE insulation, unenclosed and spaced from the surface, a 20 m run and a 2.5% maximum voltage drop. The result names the cable (for example 4C 16 mm² Cu XLPE (X-90) + earth) and the matching breaker rating.

This inline estimate is intended for early sizing. For a project-specific result that accounts for the real installation method, grouping and ambient derating, the prospective fault level, the adiabatic short-circuit withstand check and the earth-fault loop impedance, hand the design off to the full ElecAS Cable Selection calculator.

Connecting the bank — packaged PFC panel

For network-charge correction the bank is connected at the main switchboard. The single-line diagram on the page shows a packaged PFC panel — supplied complete with an integral PF controller/regulator, contactor and delta-connected capacitor bank — tapping the MSB busbar through its own circuit breaker and feeder cable, with the incomer current transformer (CT) signal feeding the regulator so the bank switches to suit the measured load.

Where the load profile varies (commercial offices, retail, mixed industrial), an automatic stepped bank switches capacitor stages on and off as the load changes to avoid leading power factor at light load. Where significant harmonic-generating load exists (variable-frequency drives, large rectifiers), detuned banks add a series reactor tuned away from the dominant harmonic, and harmonic-filtered banks add tuned filters, to prevent resonance and capacitor failure.

Reviewed by

Wisam Tozah — Associate Electrical Engineer. B.Eng (Electrical), MIEAust, CPEng, NER, NSW DBP, NSW PRE, APEC, IntPE(Aus). LinkedIn.

Frequently asked questions

How is capacitor bank size calculated for power factor correction?: The required capacitive reactive power is Qc = kW × (tanφ₁ − tanφ₂), where φ₁ is the existing power factor angle and φ₂ is the target. For a 100 kW load improving from 0.75 PF (tanφ = 0.882) to 0.95 PF (tanφ = 0.329), Qc = 100 × (0.882 − 0.329) ≈ 55 kVAR. The ElecAS calculator then rounds this up to the next standard bank size.
What target power factor should I aim for in Australia?: Most Australian distribution network tariffs apply a kVA demand charge or a power factor penalty below 0.90, and some commercial tariffs target 0.95. A practical target is 0.95 lagging — high enough to clear most penalties without over-correcting. Correcting close to unity or into leading power factor at light load can cause overvoltage and resonance, so the calculator caps the target at the existing power factor as a floor.
Where should the capacitor bank be installed?: To reduce network demand charges, install at the main switchboard (global correction) — this is the packaged PFC panel shown in the connection diagram, tapping the MSB busbar through its own CB and CT. To also cut internal cable losses and free up upstream capacity, install close to large inductive loads such as motors and transformers (local correction). Where significant harmonic-generating load exists (VFDs, large rectifiers), use detuned or harmonic-filtered banks to avoid resonance.
Why does the bank cable and breaker use a ×1.5 design current?: A capacitor bank draws more than its nominal current Ic in service: IEC 60831 allows capacitance up to +10% tolerance, sustained overvoltage up to ~10%, and harmonic currents add further loading. Standard practice is to size the bank feeder cable and protective device at about 1.5 × the nominal bank current. ElecAS computes Ic from the installed standard bank size, applies the ×1.5 uplift, and sizes the cable and CB on that design current to AS/NZS 3008.1.1.
How much will power factor correction reduce my demand?: Correcting power factor reduces apparent power (kVA) and line current for the same real power (kW). Moving 100 kW from 0.75 to 0.95 PF drops apparent power from 133.3 kVA to 105.3 kVA — a 21% reduction in kVA demand and line current. The ElecAS calculator shows the initial and target kVA, the kVA reduction and the line-current reduction percentage directly from the power triangle.
How do I calculate the required kVAR for power factor correction?: Qc = P × (tanφ₁ − tanφ₂) where P is the real power in kW, φ₁ is the original power factor angle and φ₂ is the target power factor angle. For a 100 kW load at cosφ = 0.75 corrected to cosφ = 0.95, Qc = 100 × (0.882 − 0.329) = 55.3 kVAR. The ElecAS calculator then rounds this up to the next standard capacitor bank size.
How do I find the capacitance in microfarads for a power factor correction bank?: For a delta-connected bank the per-phase capacitance is C = Qc / (3 × V² × 2πf), where Qc is the correction in VAR, V is the line voltage and f is the frequency. The ElecAS calculator reports this value in microfarads (µF) directly, so you can specify or check the capacitor step against a manufacturer rating.
What size cable and breaker does a capacitor bank need?: Size them on the bank design current, not the nominal current. The nominal bank current is Ic = (kVAR × 1000) / (√3 × V); standard practice uplifts this by about 1.5× to allow for the IEC 60831 capacitance tolerance, sustained overvoltage and harmonic loading. ElecAS applies the ×1.5 uplift and auto-sizes a compliant cable and breaker to AS/NZS 3008.1.1:2025 from that design current.
How much does power factor correction reduce demand and current?: Correcting power factor lowers the apparent power (kVA) and the line current for the same real power (kW). Moving 100 kW from 0.75 to 0.95 PF reduces apparent power from 133.3 kVA to 105.3 kVA — about a 21% reduction in kVA demand and line current. The ElecAS calculator shows the initial and target kVA, the kVA reduction and the line-current reduction percentage.
Can over-correction cause problems?: Yes. Over-correction at light load produces a leading power factor which can cause voltage rise, damage motors and trip generator-set protective relays. Avoid it by sizing the bank to a realistic target (around 0.95) rather than unity, and by using an automatic stepped bank that switches capacitor stages on and off as the load varies.
Where should a power factor correction bank be installed?: To reduce network demand charges, install at the main switchboard (global correction) — the packaged PFC panel shown in the connection diagram, tapping the MSB busbar through its own CB and CT. To also cut internal cable losses and free up upstream capacity, install close to large inductive loads such as motors and transformers (local correction).