Hall of shame

I'd love to see/hear this IRL

Avpx

I still don't follow this. Are you saying the supply voltage was 100 Volts (which would surprise me greatly) or that the supply voltage was something like 200 Volts dropped to 100 Volts by the light bulb. What is the relevance of the train being derailed? Surely this would not affect the voltage of the live rail?

In message snipped-for-privacy@4ax.com, Scott snipped-for-privacy@gefion.myzen.co.uk> writes

Not if you put your fingers across live and neutral like what I did recently.

They only trip if you go between live and earth, or short neutral and earth.

Brian

Yes. T shirts are available :-)

Sometimes...

BUT the key is that you are mostly earthed anyway and an RCD should trip even if you are touching neutral as well.

I don't know what the voltages were before and after dropping, but clearly if the train isn't taking any current the voltage will rise to the supply voltage.

Up until the major refurbishment around the Millennium, the stage machinery for the Royal Opera House, Covent Garden, was driven by WW1 submarine motors supplied with DC through mercury arc rectifiers. (Of course the motors would be DC as the submarines were powered by lead acid batteries.)

I went on tours of the ROH before and after the refurbishment. I should have asked to see the rectifiers if possible.

When i used to work at Pye Television transmitters we had a three phase transformer that used to wind up the 415 volt AC mains to around 15 kV for the high voltage Klystron supplies we were supplying these units to Korea IIRC.

Anyway one of the Korean men showed us how to check the 15 kV supply was off, he just banged the earthing stick across the incoming mains on the transformer.

Bloody great bang and flash and the whole factory went out, he was shall we say shaken and stirred!...

Hornby basically copied the method already used by the German toy makers of the early 20th century who were no longer popular in Britain after WW1. Ironically just as the Germans were deciding that it was too dangerous. Have a read of this which may answer your questions

GH

Many years ago, when I was naive and developing CRT-based PC display systems, I was trying to solve a jitter problem. To rule out anything from the supply side I built a huge capacitor bank so I could run the display from DC for a while. I knew the caps should have bleed resistors but I didn't have anything suitable, and time was short, so didn't bother with them. I finished the test and left the kit for a few hours. When I returned to dismantle everything I decided to check it was safe by shorting with a screwdriver. The resulting bang affected my hearing for a looong time (and may still be doing so), people came running down the corridor (I was in a separate office, with the door shut, for safety) because they thought there had been an explosion, and most of the screwdriver had disappeared. I knew about the need for bleeds, and about the dangers of dielectric absorption, from Uni and earlier work but was overconfident. Hubris lead to (near) nemesis. I was shaken, stirred, ... and deaf!

Thanks for the link.

When I worked at a supplier of large, industrial compressors, we had one on the test stand, with a 3.5MW, 11kV, 3-phase motor. The Electrical Engineer in charge of test supplies fired in the local breaker - unfortunately, he'd not told anyone else and people were working on the unit. Luckily no-one was hurt, but as the motor still had a set of earthing bars across its inputs, there was a large bang, a flash, smoke and the local breaker fired straight back out ... as did the one in the distribution room; the one in the electricity board's end of the distribution room; the one in the sub-station; the one feeding that substation; and, IIRC, the one feeding the supplies further up the chain. The factory, offices, dozens of other businesses and the local council estate (around 14,000 homes) were blacked out and it took 3 hours before supplies were restored.