What is Leakage Current? DC Leakage VS AC Leakage

Leakage Current Definition

When any unwanted current flows from any live part of the electrical system to the ground it is called a Leakage Current. Generally, the leakage current flows through the undesirable conductive path. Basically, the leakage current causes different types of faults which are known to us as earth faults, ground faults, residual current faults, etc. Leakage current may be very small in magnitude or very large in magnitude according to its conductive path, system voltage, types of fault, etc. A common example of leakage is human electric shock. Yes, when a person gets an electrical shock the current flow through that person's body can be called a leakage current.

Causes of Leakage Current

There are several causes of leakage current such as,

1. Human Electrical Shock
2. Insulation Failure
3. Virtual Shunt Capacitance in Power Lines
4. Using of Bypass Capacitor, Y Capacitors in EMI Filters, etc.
5. Activation of surge protectors

Types of Leakage Current

There are two main types of leakage currents,

1. AC Leakage Current
2. DC Leakage Current

The other types of leakage currents are high-frequency noise signals, surge currents, etc.

AC leakage you will see in the electrical power transmission and distribution lines whereas DC leakage is mostly seen in end products and devices. The high-frequency noise signal leakage can be seen in filter circuits, etc.

AC Leakage Current

The leakage current alternating in nature is called AC leakage current. As we know that our electrical power distribution and transmission system is based on alternating current. So, you will see most of the leakage current faults that happen in power lines are AC leakage current.

DC Leakage Current

The leakage current is a direct, constant, and steady state in nature and is called a DC Leakage Current. DC leakage means Direct Current Leakage. We know most of the electronic devices are designed to work with a DC power supply so the leakage current that happens in those devices is DC leakage current.

Leakage Current Measurement

There are various types of meters are available in the market to measure the leakage current. Some of them are designed to measure the leakage current by flowing it through them. That means the meter is connected in series with the grounding line so it can measure the current when flowing through it. These devices have limitations because they can measure the leakage current in a particular conductive grounding path. 

Another type of earth leakage current meter is designed to measure the leakage current by the residual current principle. Basically, they continuously monitor the current flow through phase and neutral. Equal current flowing through the phase and neutral indicates there is no leakage current but if unequal current flows through the phase and neutral that means there is leakage current anywhere in the system. Remember that the residual current principle works with alternating current.

You will see for a very low current measurement, generally, the resistor or resistor-capacitor network is connected in series. Then the voltage drop across them is measured by a sensitive voltmeter.

The safe level for Leakage Current

According to IEC 950 safety standards,

• The maximum accepted leakage current is 0.25 mA for double-insulated products or system
• For a grounded system, 0.75 mA for a handheld system, and 3.5 mA for a stationary or permanent system.
• For medical equipment 0.5mA under normal conditions and 1mA for single fault conditions.

Effects of Leakage Current

1. Leakage current causes unwanted electrical power loss.

2. Leakage current makes unstable and unbalanced the system voltage.

3. Leakage current can create unwanted heat in the system.

4. Leakage current creates chances of electrical shock and equipment damage.

Leakage Current Protection

There are various safety and protective devices available in the market for leakage current protection. For example, the ELCB or Earth Leakage Circuit Breaker gives protection using the current sensing or voltage dropping principle. On the other hand, the RCCB or Residual Current Circuit Breaker gives protection using the residual current measurement principle.

Read Also: 

• Examples of Common Electrical Faults
• Transient Voltage Cause, Sources, Effects, Protection
• Difference between Earth Fault Relay and Earth Leakage Relay
• The List of Faults RCCB can Protect and Can't Protect
• List of Electrical Safety/Protective Devices used in Home

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