Circuit Breaker and Residual Current Device: What Is the Difference?

In today’s world, many people think that a circuit breaker and a residual current device are the same device. However, one protects cables and the electrical installation, while the other directly saves your life.

Circuit breakers protect your electrical installation against short circuits and overloads, while residual current devices protect you against electric shock and fires caused by leakage current. The working principles and purposes of these two devices are completely different. Therefore, these two devices are not alternatives to each other; they are indispensable complementary components of a safe electrical system.

What Is a Circuit Breaker?

Circuit breakers are miniature circuit protection devices that protect the electrical installation by using a bimetal structure against overloads (thermal protection) and a magnetic coil structure against short circuits.

Overload protection, also known as thermal protection, is activated when current above the cable’s capacity passes through it. Inside the circuit breaker, there is a bimetallic strip made of two metals with different expansion coefficients. As the current increases, this strip begins to heat up. Since one of the metals expands more than the other, the strip bends. The bent bimetallic strip touches the tripping mechanism of the breaker and opens the circuit, meaning the breaker trips. However, this protection does not happen instantly; it occurs as the cables heat up over time. The higher the current, the faster the bimetal heats up and the faster the circuit is cut off. Its purpose is to prevent the cable insulation from melting and to prevent fire.

What Is a Residual Current Device?

A residual current device is a vital protection component that ensures life and property safety by protecting against electrical leakage currents. Its working principle is based on one of the most fundamental laws of electricity: the first rule of Kirchhoff’s Current Law, namely the principle of conservation of charge in electrical circuits. According to this principle, the current entering a circuit must be equal to the current leaving the circuit. Otherwise, there is a loss in the circuit, meaning a leakage current exists. This leakage has found another path instead of completing the circuit through the normal route, which is the neutral line.

As a result:

Electric Shock: If there is an insulation fault and a person touches this device, the leakage current flows through that person’s body to the ground. In other words, electric shock occurs, which is a major danger to human life.

Arc Formation and Fire: Even small leakage currents can, over time, cause arcs and fires at the point where they flow.

The Critical Difference Between 30 mA and 300 mA

In residual current devices, the 30 mA and 300 mA thresholds determine the sensitivity of the device and what type of protection it provides.

30 mA, known as the “life protection threshold,” is designed to directly protect human life.

According to research, electric current above 30 mA can cause heart rhythm disorders and even death. A 30 mA residual current device cuts off the electricity before the current reaches this fatal threshold, usually within 15–20 ms. This protects people from electric shock. The use of 30 mA residual current devices in homes and offices is a legal requirement.

300 mA, known as the “fire protection threshold,” is designed to prevent fire risks.

A leakage current of around 300 mA in an electrical installation can cause electrical arcs and generate enough heat to ignite surrounding materials. Such leakage can be fatal for a person, but this threshold is considered ideal for protecting a building against electrical fires. A 300 mA residual current device is installed at the main entrance of the building, in the main distribution board next to the meter. If a 30 mA device is installed at the main entrance, even the smallest leakage in the home can cut off the electricity of the entire building. Therefore, 300 mA is used at the main entrance as a selectivity element.

Critical Points That Distinguish a Circuit Breaker from a Residual Current Device

Based on this information, we should understand that having a circuit breaker in your home does not mean you are protected against electric shock and fire. For full protection in an electrical installation, both devices must be present at the same time. The circuit breaker is designed to protect the installation and cables. The true hero that directly saves your life is the residual current device.