Glossary term
Leakage Current
Unwanted or unintended electric current that flows through insulation, devices, or parasitic paths.
Definition
quantityLeakage current is unintended current that flows through insulating materials, semiconductor junctions, protective paths, or parasitic impedances.
No insulation or semiconductor junction is perfectly nonconductive. Small currents can flow through dielectric materials, across contaminated surfaces, through reverse-biased junctions, through capacitive coupling, or along protective earth paths. Leakage current matters for electrical safety, battery life, standby power, sensor accuracy, insulation health, medical equipment, high-voltage systems, and semiconductor reliability.
Leakage current is current that flows where the ideal model says little or no current should flow. It may pass through insulation, across surfaces, through reverse-biased semiconductor junctions, through capacitive paths, or through protective earth conductors. The magnitude may range from nanoamperes in precision electronics to milliamperes or more in power equipment.
Mechanisms
In insulation systems, leakage can be caused by moisture, contamination, ageing, thermal damage, cracks, surface tracking, high electric field, or insufficient creepage and clearance. In semiconductors, leakage current can arise from reverse-biased junctions, gate oxides, subthreshold conduction, temperature-dependent carrier generation, and device defects. In AC equipment, capacitive coupling between conductors and grounded structures can create normal leakage even when insulation is healthy.
Temperature is often critical. Semiconductor leakage generally increases strongly with junction temperature. Insulation leakage can also increase with temperature and humidity.
Why it matters
Leakage current affects safety and performance. In electrical installations, excessive earth leakage can trip residual-current devices or indicate insulation deterioration. In medical equipment, patient leakage limits are strict because small currents can be hazardous. In battery-powered electronics, leakage reduces standby life. In sensors and high-impedance circuits, leakage can corrupt measurements. In high-voltage systems, leakage can lead to heating, tracking, partial discharge, or ground faults.
Measurement
Leakage current is measured with appropriate meters, insulation testers, electrometers, current probes, or safety analyzers depending on magnitude and context. The measurement must define voltage, polarity, frequency, temperature, humidity, settling time, and path. For very small currents, cable insulation, board contamination, guarding, instrument bias current, and electrostatic charge can dominate the reading.
Common mistakes
A common mistake is treating any leakage as a fault. Some leakage is expected in filters, capacitive coupling, and semiconductor devices. The engineering question is whether the value is within the specified limit for the condition. Another mistake is measuring leakage without reproducing operating voltage, temperature, humidity, or frequency. Good reports state the applied voltage, measurement path, environmental condition, acceptance limit, and whether the current is DC, AC, earth, touch, patient, or device leakage.