- Reaction score
- 13,475
Some good points there Alasdair. The likely inaccuracy of measurement of non-sinusoidal voltage should have been raised at the time, but I think we got bogged down trying to work out whether the drop referred to was in the switch or the supply cable. In any case we never even found out what instrument took the measurements. It's still not clear to me how any significant drop could have occurred in the switch as the mean dissipation could not have been more than a few dozen watts without visible signs of overheating. The damage within the case loooked more like the result of brief, intense arcing, such as when closed onto a short.
To put this to bed, I would like to do a practical test of the sensitivity of an MCB to extreme waveforms, e.g. by playing an arbitrary waveform generator through a laboratory amplifier and transforming down to get a test supply of up to say 100A pk. My hunch is that the MCB will stay in spec for thermal tripping accuracy wrt. RMS current, but the magnetic trip could do anything. I might try this if the Christmas celebrations start to drag on too long. However, since there was a resistive load (we think) in series at all times, we were generally in agreement that the magnetic trip was never involved.
The bottom line is that although we know how the fault was cured, we don't truly know the nature of the fault itself.
To put this to bed, I would like to do a practical test of the sensitivity of an MCB to extreme waveforms, e.g. by playing an arbitrary waveform generator through a laboratory amplifier and transforming down to get a test supply of up to say 100A pk. My hunch is that the MCB will stay in spec for thermal tripping accuracy wrt. RMS current, but the magnetic trip could do anything. I might try this if the Christmas celebrations start to drag on too long. However, since there was a resistive load (we think) in series at all times, we were generally in agreement that the magnetic trip was never involved.
The bottom line is that although we know how the fault was cured, we don't truly know the nature of the fault itself.