I expect the answer is somewhere in this forum but if someone can quote me a figure or point me in the right direction, I would be grateful. I am seeking to establish what sort of overcurrent would cause a 45 Amp Type B MCB to trip in approx 10 secs. The device is protecting a shower circuit wired in 10mm2 twin and earth. The circuit is further protected by a two pole RCD rated to trip @ 30mA. Presumably the MCB is tripping thermally rather than magnetically as it buzzes for a few seconds before dropping out. I believe this points to a fault in the shower unit itself (an Aqualisa rated at 10.5KW) rather than the associated circuit. The RCD has not tripped at all and I have already replaced the MCB and the double pole pull switch, to eliminate the possibility that either of those items was the cause of the problem.
Tripping current for Type B MCB
- Thread starter spongsdad
- Start date
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Looking at the graphs in the IEE regs for type B MCBs a 10s disconnection is at 5x its rated current which is doubtful as at 5x it should have already tripped at 0.1s.
You are probably correct in the shower itself causing the problem, one way to tell how much current is being drawin by the shower is by using a clamp on ammeter, do you know any electricians who may have one?
You are probably correct in the shower itself causing the problem, one way to tell how much current is being drawin by the shower is by using a clamp on ammeter, do you know any electricians who may have one?
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The Aqualisa visit referred to above is the second by the engineer. He visited last week and replaced (I believe) the heater unit or heat exchanger. I'm not certain because I was out and he dealt with my wife.
However Aqualisa report that the part replaced was not faulty. The MCB is rated at 45A for a 10.5 KW device. If the shower is rated for 230V would this MCB be too close for comfort for a supply overvoltage of 10%. In other words would I be likely to get random and spurious tripping? I am reluctant to uprate the MCB to 50A but would this be the better option?
However Aqualisa report that the part replaced was not faulty. The MCB is rated at 45A for a 10.5 KW device. If the shower is rated for 230V would this MCB be too close for comfort for a supply overvoltage of 10%. In other words would I be likely to get random and spurious tripping? I am reluctant to uprate the MCB to 50A but would this be the better option?
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