Arcing contact problems and voltage measurements - some thoughts

[Lucien Nunes]

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.

 

[Bul]

I think that this has been the most interesting post of the year !

 

[ipf]

The bottom line is that although we know how the fault was cured, we don't truly know the nature of the fault itself.

I think that sums things up pretty well, Lucien.

 

[static zap]

TESTS.... 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. ...The magnetic trip could do anything. I might try this if the Christmas celebrations start to drag on too long..

Have wondered if arc may have fluctuating DC componenets that may be occasianally reversing . If the intermitency - hits natural resonance
with occasional impulses .(Sods law and when you want random symetry ... a DC componenet may desensitize ... magnetize ..then reverse (expecting resonances to change with manufacturer geometry)
-- Keep up the up the LAB work Lucien --

....... in extreme cases heating of the skin.

We were warned eye corneas have little blood flow to remove heat ..
(remembered watching my dinner in the microwave -- cyclic pattern)

 

[Midwest]

I think that this has been the most interesting post of the year !

It would be, if I knew what the hell they are banging on about. I reckon they are just taking the ----, and saying anything that comes into their heads.