What is ELCB and Why ELCB is needed?

Definition of ELCB

ELCB is a molded case circuit breaker used in a low-voltage AC electrical circuit to provide electric shock protection and prevent fires from current leakages. ELCB is called a “Circuit-breaker incorporating residual current protection” (IEC60947-2) or a “Residual current operated circuit breaker” (IEC61009-1). It is also referred to as a “Ground-fault circuit-interrupter” (UL943). There are two types of ELCB, a current-operated type and a voltageoperated type. In many countries, only the more beneficial current operating-type is manufactured. The Japanese Industrial Standards (JIS) apply only to the current-operated type. In terms of ELCB structure, the product is defined as a “device with integrated ground fault detector, tripping device and swi tch mechanism in an insulated body, and automatically shuts off the electric current in the event of a ground fault.”

History of ELCB

The low-voltage electrical circuit is originally a nongrounding circuit. However, after it became possible to use an alternating current to reduce a high-voltage to a low voltage with a transformer, the risk of contact of high and low voltages and the risk of double ground faults increased. Subsequently, the use of grounded systems became mainstream. Of course, there are still some non-grounding circuits, but most are grounded circuits. In Japan and the United States, priority has been placed on preventing fires from ground faults. Most protective grounding systems reduce the voltage and ground the device frame. Conversely in Europe, 220 V voltage systems are used in homes, so there has been an interest in ELCB from an early stage. The initial ELCB was a voltage-operated type, and the protection range was small . There were many disadvantages in the use.etc. Today, most units adopt the current operating type.

Why ELCB is Needed?

Awareness toward electric shock injuries and short-circuit fires has increased in view of saving human life and assets. In addition, places requiring installation of ELCB has increased for legal reasons. Conventionally, electric shocks were prevented only with protective grounding work. While this was effective, it was found to be insufficient when stricter conditions were considered.

  

In Fig. 6. 1 for example, if the motor M insulation degrades and generates a potential at the motor frame, the voltage to ground Vg is expressed with the following expression.

RL is a low value that can be ignored compared to R2 and R3.

Thus,

With IEC60364-4-41, the contact potential must be 50V or less to protect humans against electric shock. In the 230/400V power distribution system, the maximum voltage to ground of an electric facility that could come in contact with humans is 230V, Thus, if Vg = 50 and E = 230, then expression (3) can be established from expression (2).

If R2 is controlled to approx. 20 ohms, R3 must always be kept to 5.6 ohms or less to enable electric shock protection with only the protective grounding method. This is not a complete electric shock completion method. If a residual current circuit breaker is used, the “power supply breaking” means is added to the “protective grounding”, and more complete electric shock protection measures are established. The size of the ground fault current differs according to the grounding method so it is essential to select the appropriate overcurrent breaker that can detect a relatively large ground fault current (MCCB or fuse) or ELCB that can detect a minute ground fault current.