A domestic MCCB is marked 25A, 6 kA, 230V AC. Which fault current will this MCCB safely interrupt?
Any fault current up to 6,000 A
To solve this question, we need to understand the specifications on the MCCB (Molded Case Circuit Breaker) and what they signify:
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Rated Current (25A): This is the maximum load current the MCCB can carry without tripping. It indicates that the MCCB can handle continuous currents up to 25 amperes without operating (i.e., tripping).
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Breaking Capacity (6 kA): The breaking capacity, or interrupting capacity, defines the maximum fault current that the MCCB can safely interrupt without damage. Therefore, an MCCB marked with 6 kA can interrupt fault currents up to 6,000 amperes safely.
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Nominal Voltage (230V AC): This indicates the standard voltage for which the MCCB is designed to operate. Here, 230 volts is the supply voltage for which the device is suitable.
Now, analyzing the options:
- Option A: "Any current at 230 V AC" - This is incorrect because it does not consider the limits of fault current or overload.
- Option B: "Any fault current up to 6,000 A" - This matches the breaking capacity specification of 6 kA, thus is correct.
- Option C: "Any overload up to 25 A" - Incorrect, as overload relates to operating current, not fault interruption capacity.
- Option D: "Any short-circuit above 25A" - This is incorrect. Fault interruption refers to the ability to interrupt short-circuits up to the breaking capacity, not just above 25A.
Therefore, the MCCB can safely interrupt "Any fault current up to 6,000 A". Thus, the correct answer is:
Any fault current up to 6,000 A
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