Hi, I'm designing a circuit with 2 MCB's in it, (not 2 circuits in 1 MCB). At my consumer unit I have a 20A C MCB with a Kn 6000. I want to then protect the appliance with a 6A C MCB with a Kn 6000. in the event of a Short circuit (Not an Overload) will the smaller MCB trip before the bigger breaker?
Design circuits with MCB's
- Thread starter Cambello
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Not sure I understand the question. What are you trying to achieve and why do you think you need type C breakers ?
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Type B trip between 3–5 times thermal setting, C 5-10 and D 10–20. We add 5% for safety, but the start point has to be prospective short circuit current or loop impedance before one can start on the design.
But if the short circuit can result in over 200 amp to flow, then both devices should trip in the same time, so there will be no discrimination between them. Either could trip, or both.
Even when there should be discrimination, I know when a worker put a nail in the Portakabin wall to hang his coat, the 30 mA, 100 mA, and 1 amp RCD's all tripped even when the 1 amp one had a one-minute delay set.
To get discrimination, you would need to use a fuse.
But if the short circuit can result in over 200 amp to flow, then both devices should trip in the same time, so there will be no discrimination between them. Either could trip, or both.
Even when there should be discrimination, I know when a worker put a nail in the Portakabin wall to hang his coat, the 30 mA, 100 mA, and 1 amp RCD's all tripped even when the 1 amp one had a one-minute delay set.
To get discrimination, you would need to use a fuse.
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