What is Surge Current Capacity in RCCB or RCD?

If you are going to purchase an RCCB or RCD, that time you will notice the term 'Surge Current Capacity' in its specification details. Sometimes we need to select an RCCB for purchase according to surge current capacity requirements. So, in this article, we are going to know what is Surge Current Capacity in an RCCB or RCD. RCCB stands for Residual Current Circuit Breaker and RCD stands for Residual Current Device. Both are almost the same devices.

What is Surge Current?

The high amount of excess current flowing in a circuit due to a sudden increase in voltage or voltage imbalance is called Surge Current.

In the below diagram, you can see the sudden increase in voltage which causes the flow of surge current in an electrical circuit.

Surge current generally flows in a circuit for a very short time duration, it may be a few seconds or milliseconds. The amplitude of a surge current flowing in a circuit may be 10 to 15 times more than the amplitude of the normal current. Surge current occurs in a circuit, due to instant switching, voltage imbalance, equipment faults, sudden increase in load, lightning, etc.

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Surge Current Capacity in RCCB or RCD

According to the IEC 61008 and IEC 61009 standards, RCDs should be able to withstand 200A ring wave impulse or surge current, and RCDs classified as 'Selective' should be able to withstand 3000A surge current of the specified waveform.

Suppose an RCCB has a surge current capacity of 250A. That means that RCCB can withstand up to 250A surge current when any fault or voltage imbalance occurs.

It is a must need to check the surge current capacity of an RCCB during the purchase which is to be used with induction motors, transformer circuits, capacitive loads, etc. Because during the starting of the induction motor surge current occurs. If you use a surge protector or suppressor, that will not be able to prevent the surge current because the surge protector is designed to suppress voltage not surge current.

So surge current capacity of an RCCB is very important because if the amplitude of the surge current or impulse current is below the surge current capacity of the RCCB, it cannot cause any harm. Suppose in a circuit, a maximum 200A surge current flow is possible. For that circuit, that RCCB is suitable which has a surge current capacity of 250A.

Why Surge Current Capacity of an RCCB or RCD is Important?

The surge current capacity of an RCCB or RCD is important because it helps them handle sudden high surges of electric current without turning off. Because if our RCCB frequently turns off due to a normal surge current then it can affect our work as well as system performance. When you connect electrical equipment to a power source, there can be a temporary increase in the amount of electric current flowing through the wires and it is acceptable also.

This surge of current is normal but can be much higher than the regular flow of electricity. If the RCCB or RCD is not able to handle these surges, it may mistakenly turn off the power supply, even though there is no real problem. By having a higher surge current capacity, the RCCB or RCD can tolerate these surges without shutting off the power unnecessarily, ensuring that your electrical devices can start up smoothly and work properly.

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