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Brymen BM235 10A fuse silently destroyed by a switched off UPS leakage current..

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hgg:
"1kA or so of PSC" and not even the smallest spark on the multimeter leads?

Cnoob:
I look at Bussmann's graph for that particular fuse which is call a clearance graph of time v current.
Assuming I reading the graph right.

I'm reading that graph as the time taken for the fuse to clear a fault condition and as this was a short circuit near instantaneous currents are involved. How high ? it depends on your impedance of your voltage source. I think it's safe to assume it's a high current and on the graph. A near instantaneous current of 150 Amps the fuse will act in 15mS. I suspect the fuse could act quicker but Bussmann are erring on caution.

So it is quite possible for that fuse to blow before the RCD can trip.

dmills:
Yep, RCDs are not (Unless RCBOs) overload sensitive, they will pass a lot of current and merely get hot, overload protection is a different type of breaker.

I would expect a LOT more then 150A in a dead short to 'earth' situation assuming TN-C-S or TN-S supplies are in use (TT, the fuse might not even have blown in a week! This is NOT a good thing!).

Like I say, THIS is why good multimeters have expensive fuses, quite possible a kA or so flowed, but probably the only part that failed was the fuse, and it kept all the damage contained inside the fuse housing, quite impressive actually.

Regards, Dan.

hgg:
Do you think that not seeing any sparks was expected ?

IanB:

--- Quote from: hgg on March 07, 2019, 12:48:21 pm ---"1kA or so of PSC" and not even the smallest spark on the multimeter leads?

--- End quote ---


--- Quote from: hgg on March 07, 2019, 03:39:54 pm ---Do you think that not seeing any sparks was expected ?

--- End quote ---

You tend to get more of a spark when breaking a circuit than when making it. I have shorted 240 V mains a couple of times in the past, and it was not very dramatic. I hardly noticed I'd done it until afterwards, when the fuse had blown or the breaker had tripped. Each time I had just barely touched a live wire against a grounded terminal and that was enough to trip the circuit protection.

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