Calculator
Example Data Table
| Case | Voltage | Length | Capacitance | Insulation | Filter leakage | RCD rating | Typical use |
|---|---|---|---|---|---|---|---|
| Office circuit | 230 V | 80 m | 180 nF/km | 100 MΩ | 0.50 mA × 6 | 30 mA | Computers and monitors |
| Drive feeder | 400 V | 120 m | 250 nF/km | 50 MΩ | 3.50 mA × 1 | 100 mA | Motor drive supply |
| Lighting run | 230 V | 160 m | 150 nF/km | 200 MΩ | 0.25 mA × 12 | 30 mA | LED lighting branch |
Formula Used
Voltage to earth for three phase line voltage:
VPE = VLL / √3
Total cable capacitance:
Ctotal = capacitance per km × cable length km × parallel runs
Capacitive leakage current:
Ic = 2 × π × f × Ctotal × VPE
Insulation leakage current:
Ir = VPE / Rinsulation
Total leakage current:
Itotal = Ic + Ir + filter leakage + extra leakage
Touch voltage estimate:
Vtouch = Itotal × earth path resistance
The calculator uses milliamp values for display. It converts amps to milliamps by multiplying by 1000.
How To Use This Calculator
Choose the supply type first. Enter the voltage and select whether it is line-to-earth or line-to-line. Add frequency, cable length, cable capacitance, and the number of parallel cable runs. Enter insulation resistance from test data when available. Add filter leakage per device and the number of connected devices. Use extra leakage for measured values or known manufacturer data. Enter the protective device rating and preferred working limit. Press calculate. Review total leakage, touch voltage, trip margin, and status.
Understanding Earth Leakage Current
Earth leakage current is the small current that leaves live conductors and returns through earth, protective conductors, cable screens, filters, or insulation paths. A tiny amount is normal in many modern systems. Drives, computers, heaters, long cables, and power supplies often add leakage. The concern begins when the total current approaches the trip level of a protective device.
Why Leakage Matters
Leakage current affects safety and reliability. Too much current may raise touch voltage on bonded metalwork. It may also cause nuisance tripping of residual current devices. A circuit can look healthy during a simple load test, yet still have high leakage because capacitance and filter components are connected to earth. Long cable runs can increase the capacitive part. Poor insulation can add a resistive part.
Key Inputs
This calculator separates leakage into common paths. Cable capacitance is estimated from length, capacitance per kilometer, frequency, and voltage to earth. Insulation leakage is estimated from voltage and insulation resistance. Filter leakage is added from connected equipment. Extra leakage lets you include measured values from meters or manufacturer data. The balance factor helps with three phase estimates where leakage may cancel partly.
Using The Result
The total current is compared with the chosen protective device rating. A working margin is also shown because installations should normally operate well below the trip point. The result is not a replacement for testing. It is a planning and checking aid. Use proper instruments, isolate circuits safely, and follow local electrical rules. For critical systems, ask a qualified electrical professional to review the design.
Practical Tips
Keep cable lengths realistic. Use manufacturer capacitance values when available. Enter insulation resistance measured under suitable test conditions. Add every connected device that includes an earth filter. If the calculator shows a low margin, reduce grouped equipment, split circuits, improve insulation, or select correct protection after a safety review. Document your assumptions. Then compare them with measured leakage during commissioning. Record ambient conditions and supply voltage, because both can change values. Retest after repairs, cleaning, or cable changes. Trend readings over time. A rising trend can reveal moisture, damaged insulation, ageing filters, or contamination before a fault becomes dangerous. It also supports clearer future maintenance decisions.
FAQs
What is earth leakage current?
It is current that flows from live conductors to earth, protective conductors, screens, or exposed metalwork. It may come from insulation resistance, cable capacitance, or filter components.
Is all leakage current dangerous?
No. Small leakage is common in modern equipment. It becomes a concern when it raises touch voltage, causes nuisance tripping, or indicates insulation deterioration.
Why does cable length affect leakage?
Longer cables usually have more capacitance to earth. More capacitance allows more alternating current to flow through that path, especially at higher frequency.
What does the balance factor mean?
It adjusts three phase leakage estimates. Use 100 percent for conservative arithmetic addition. Use a lower value when balanced leakage cancellation is expected and justified.
Can this replace insulation testing?
No. It is an estimate and planning tool. Use suitable test instruments and safe isolation methods before working on electrical circuits.
Why include filter leakage?
Many drives, computers, power supplies, and appliances include filters connected to earth. Their small currents can add together on shared circuits.
What is a good leakage margin?
Many designers aim to stay well below the protective device trip rating. A common planning target is 30 percent or less, but local rules matter.
Why calculate touch voltage?
Touch voltage estimates the voltage that may appear across the earth path resistance. It helps highlight possible shock risk under leakage conditions.