Vintage Electrical Hazards BBC4

[OscarFoxtrot]

I don't think that cross-head screw's authentic.

[Herald1360]

It doesn't need to be. It's a recent installation of an old switch "for appearance". You can't see it with the top on.

[emeritus]

The attached PDfs contain the entire range of GEC's domestic switches from their 1893 and 1911-12 catalogues. While the woodcuts show the mechanism quite clearly, nothing is said about the insulation between toggle and contacts, other than the "Home Office" model that uses a ceramic toggle.

In 1893, rotary swiches predominate, and in their toggle switches, the toggle lever seems to move a sliding bolt having a conductive tip to bridge the contacts.

The switch in the photo of #20 isn't identical with any of GEC's offerings, although the design is similar to their Edwardian range. The ceramic base seems much deeper for one thing. Interestingly enough, it seems that by 1911 the Home Office had had reservations about the use of unearthed metal covers in this type of switch, and their contemporary regulations apparently prohibited them: see page 783, see the last page of the "1 of 2" file. Nonetheless GEC continued to supply such switches, but of course there were still significant mains installations of 110V and private installations of around 50V in the UK, and GEC did export to countries with less stringent regulations.

Even in 1893, test equipment for measuring insulation resistance was readily available, for sale of hire, although only testing at about 100V in line with contemporary practice. By 1911, a range of insulation testers were available that could test at 500V and even 1000V . There's a thread dealing with early Meggers here:

https://www.vintage-radio.net/forum/...d.php?p=597444

[Heatercathodeshort]

Originally Posted by OscarFoxtrot

I don't think that cross-head screw's authentic.

There had to be one.. J.

[Herald1360]

I rather like the idea of "sweating terminals" on the 30A version of the switches in attachment 1

[emeritus]

I forgot to mention that the height of each page is 10 1/2". The drawings are said to be to scale and this might be of interest for determining the dimensons of the illustrated items. I included the top and bottom edges of each page of the scans for that reason.