Mercury contactor

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I spotted one of these out in the wild today. Still in service and working perfectly switching a bank of night storage heaters. Don’t see very many of them these days.

AAC1FA10-27F4-4109-82F2-2F408E98CD35.jpeg
 
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Only ever seen one of those before in the flesh. In my first year of working as an apprentice, 1983!
 
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Weused to have a few mercury relays in the rectifiers at work. the leads had a series of ceramic beads on the bare multistranded leads.
 
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The old GPO used mercury relays to switch mains voltage with the telephone's ringing current, Often used in the old police boxes to switch the lamp on the top of the box when control room wanted to contact the officer on the beat. ( Remember those days ? )
GPO relay box 230 volt mercury.jpg



I got involved with one of these three phase to DC rectifiers at a hospital laundry. ( not this actual beast ) when I learnt the hazard of working with mercury.

ZruM3cuhwHyD1u6F_sFHUZuACh0XnXbFWeL3mg9A1cA.jpg
 
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Ahh those were the da...

Actually thank heavens we've moved on:)
 
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I know a site still using mercury relays.

24v DC fire alarm bells through out a factory. Many of the bells have a mercury relay adjacent, switching a 240v klaxon sounder.

If there’s no 230v power, the factory is silent, so bells only is acceptable.
 

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I got involved with one of these three phase to DC rectifiers at a hospital laundry. ( not this actual beast ) when I learnt the hazard of working with mercury.

ZruM3cuhwHyD1u6F_sFHUZuACh0XnXbFWeL3mg9A1cA.jpg
Would that be a similar thing to a Nevitron mercury arc rectifier?
I once saw one in use at a brewery of all places and, at the time, had no idea what the hell it was - although I was very impressed with all the blue sparks!
I believe they may have been used for X-ray machines in the Stone Age, long before my time as a radiographer, I assume to convert AC or three-phase to DC at high voltage (up to 150kV) at the X-ray tube.
 
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Would that be a similar thing to a Nevitron mercury arc rectifier?

Yes, being pedantic they are mercury vapour rectifiers as there was no arc once they had been started. The arc was created by an springy electrode that was pulled down to dip into the pool of mercury to create a spark to vapourise some of the mercury. A plasma discharge then continued to maintain the vapour.

They were used to provide the 660 volt DC traction supply for London Underground,
 

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Yes, being pedantic they are mercury vapour rectifiers as there was no arc once they had been started. The arc was created by an springy electrode that was pulled down to dip into the pool of mercury to create a spark to vapourise some of the mercury. A plasma discharge then continued to maintain the vapour.

They were used to provide the 660 volt DC traction supply for London Underground,
Thank you.

Yes, I may have been mistaken and, rather than seeing blue sparks (at the brewery), it might have been plasma.

I'm not too sure about providing 150kV DC for X-ray machines, though, as I read elsewhere that they were not used for such high voltages (or perhaps they were).
I wonder whether that might have yet been possible though, as the current across an X-ray tube would be only milliamps and even then only for a fraction of a second.
 
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rather than seeing blue sparks

Very often the "dipper" would continue to dip into the pool for some reason. Maybe in the current was too low to keep the plasma running.

Low time ago and memory has failed on the exact way they worked.
 

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