Combined Miniature circuit breaker/Residual Current Circuit Breaker MCB/RCD 1+N, AMPARO 6kA, C 6A, 30mA, Typе A

MCB (Miniature circuit breaker) is a re-settable device designed to protect a circuit from short circuits and overcurrents. Trip curves of MCB’s (B, C, D, K and Z curves) tell us about the trip current rating of Miniature Circuit breakers. Trip current rating is the minimum current at which the MCB will trip instantaneously. It is required that the trip current must persist for 0.1s.

Residual Current Circuit Breakers (RCCB) are designed to disconnect the circuit if there is a leakage current. By detecting small leakage currents (typically 5–30 mA) and disconnecting quickly enough (<30 ms), they may prevent electrocution.They are an essential part of the automatic disconnection of supply (ADS), i.e. to switch off when a fault develops, rather than rely on human intervention, one of the essential tenets of modern electrical practice.

To prevent electrocution, RCDs should operate within 25–40 milliseconds with any leakage currents (through a person) of greater than 30 mA, before electric shock can drive the heart into ventricular fibrillation, the most common cause of death through electric shock. By contrast, conventional circuit breakers or fuses only break the circuit when the total current is excessive (which may be thousands of times the leakage current an RCD responds to). A small leakage current, such as through a person, can be a very serious fault, but would probably not increase the total current enough for a fuse or circuit breaker to break the circuit, and certainly not do so fast enough to save a life.

RCDs operate by measuring the current balance between two conductors using a differential current transformer. This measures the difference between current flowing through the live conductor and that returning through the neutral conductor. If these do not sum to zero, there is a leakage of current to somewhere else (to earth/ground or to another circuit), and the device will open its contacts. Operation does not require a fault current to return through the earth wire in the installation; the trip will operate just as well if the return path is through plumbing, contact with the ground or any other current path. Automatic disconnection and a measure of shock protection is therefore still provided even if the earth wiring of the installation is damaged or incomplete.

For an RCD used with three-phase power, all three live conductors and the neutral (if fitted) must pass through the current transformer.

Technical parameters of Combined Miniature circuit breaker/Residual Current Circuit Breaker MCB/RCD 1+N, AMPARO 6kA, C 6A, 30mA, Typе A: