An unusual electrical fault to find.

Belfastman1958 · Aug 3, 2019

I work in a large public services building near my home town and it consists of wiring that was done back in the 1950's (perhaps 12/13th Edition?) when the first buildings were erected using V.I.R. cables right up to the latest 18th Edition wiring that includes "phase matched UPS/IPS" systems and "quinetic" lighting control systems.

Here are some photos of a fault that I was working on this week where there was no supply getting to a light fitting. The switches are very old mercury tilt light switches and one of the vials had fractured causing the mercury to leak out. The mercury was held at a live potential and shorted to earth. Took me ages to find the problem.

I just thought some of you would be interested to see some photos.

[ElectriciansForums.net] An unusual electrical fault to find.

westward10 · Aug 3, 2019

I have a socket somewhere with a mercury switch. So what happens now with the mercury on the loose issue.

Belfastman1958 · Aug 3, 2019

westward10 said:
I have a socket somewhere with a mercury switch. So what happens now with the mercury on the loose issue.

I was instructed to close the switchplate up and my team leader has sent for the "decontamination team" to clean out the switchbox. No doubt I'll be back to revisit it and isolate the switches from the supply for the team to work at them.

Lucien Nunes · Aug 3, 2019

Those switches are rare and interesting, thank you for posting. If there is any chance of saving any intact ones, I would be very keen to discuss. They were commonly used where explosive atmosphere might be present such as in operating theatres, but rare in general wiring work.

I once found an odd effect in an auxiliary house-lighting circuit in a theatre, where there seemed to be a short delay between operating a switch and the lights responding. This was due to a mercury relay hidden in a CI box in the wall, long since plastered over and forgotten, still controlling the circuit.

snowhead · Aug 3, 2019

I remember Mercury.
That was that interesting stuff we used to roll around the Chemistry lab desks in the 60's.

Oh, and the same stuff they mixed with glue and pushed into holes in my teeth.
Just checked , it's still in use today the NHS Amalgam fillings.

An unusual electrical fault to find.

Belfastman1958

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westward10

Belfastman1958

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Lucien Nunes

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snowhead

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