Weird wall sockets

[ericmark]

There was normally a 1A fuse fitted in the plug, so replacing with a 5 amp plug you would need to check if it needed fusing down.

 

[333rocky333]

They didn’t fit grommets back then.

Or earth links. Didn’t even have an Earth terminal in them old boxes

For Mk at least the earth lugs were always sold seperate.

Earth links were actually more common then, but likely plain Green.
Most supplies were conduit or pyro therefore the link was necessary to Earth the frontplate, this was in the Regs and still is, now the reverse use is more common, its use now, is mainly to earth the backbox.

 

[AndyPRK]

"For Mk at least the earth lugs were always sold se[perate"

How do they work then?

I've seen a house wired in 1965. It has black metal back boxes and no earth terminals

 

[333rocky333]

Not sure about the black boxes but the early steel boxes similar to the Ops had a hole with a flat side drilled in the back face.

The earth lug pushed in the hole and a brass screw went in from the back to hold it in, the flat edge stopped the lug spinning, once fitted it looks like the terminals fitted nowadays that are pressed in.

I never realised that they actually made a 5 amp and a 15 amp version

https://www.mkelectric.com/en-gb/Products/CM/conduitmini/Accessories/Accessories/Pages/BET1.aspx

https://www.mkelectric.com/en-gb/Products/CM/conduitmini/Accessories/Accessories/Pages/BET2.aspx

 

[JohnD]

There was normally a 1A fuse fitted in the plug, so replacing with a 5 amp plug you would need to check if it needed fusing down.

the clock plug has an unusually small fuse in it.

I think I have a few in a box in the loft, they were never easy to come by so I got a bag of spare fuses with the outlets. I don't know when electric clocks went out of fashion and battery Quartz ones came in, but the little sockets and plugs continued being used for extractor fans in office buildings, which is very neat for maintenance and replacement. A circuit that supplies clocks can't afford to be turned off.

Nothing else fits the socket, and the plug is retained with a thumbscrew.

 

[winston1]

the clock plug has an unusually small fuse in it.

They are also used in 5a and 2a fused plugs from MK. They are basically the same size as 20mm fuses found in electronic goods. 20mm fuses are usually glass, but ceramic ones are available.

 

[plugwash]

The small fuses you see in clock connectors, MK fused round pin plugs and many shaver adapters are BS646 fuses.

As you say they are very similar in size to 20mm fuses. Close enough that they will interchange mechanically. CPC sell them though thye are fairly expensive.

 

[JBR]

I don't know when electric clocks went out of fashion and battery Quartz ones came in

Slightly off-topic, I apologise, but I have been looking for an old electric clock for a long time now and finally, earlier this year, I found one for sale and snapped it up. It was advertised as working, but ought to be checked.

I checked it and ensured that the internal wiring was sound. There is no earth wire. It works perfectly, I'm pleased to say. As expected, it is quite accurate too. Throughout the day, although it may become several seconds fast or slow because the mains frequency is not always exactly at 50 Hz, over a longer time it keeps very accurate time. I assume that is because, whilst the frequency dips below and rises above 50 Hz, it averages out at virtually exactly 50 Hz over a longer term.

 

[ban-all-sheds]

AIUI "long-term" averaging at 50Hz is a requirement of the DNOs specifically because of electric clocks.

 

[JBR]

Yes. Here's a 'live' indication of mains frequency. Requires Flash Player.

http://www.dynamicdemand.co.uk/grid.htm#

 

[EFLImpudence]

https://www.gridwatch.templar.co.uk/

 

[gazzagadget]

In the 70's we used these 'clock points' for supplying mains power to indoor CCTV security cameras. Camera's were almost all mains powered in those days and clock points provided a compact & convenient power connection.

 

[bernardgreen]

AIUI "long-term" averaging at 50Hz is a requirement of the DNOs specifically because of electric clocks.

I do not know about the present "standard" but in the 50's and 60's they counted the number of cycles over the whole day and if it was not 4320000 ( +/- a very small tolerance ) then some one got a bit of a reprimand

( the required number = 50 x 60 x 60 x 24 )

 

[JohnW2]

In the 70's we used these 'clock points' for supplying mains power to indoor CCTV security cameras.

In the same era (and 80s) I used them to supply lights above bookcases etc..

Kind Regards, John

 

[stem]

Some relatives of mine used to own a cabaret / restaurant / banqueting suite. They had table lamps connected to them that were wired to 5A lighting circuits. The advantages were.

1) It allowed the lamps to be remotely controlled from the light switches and even dimmed if required, according to the function in progress.
2) The cleaners couldn't plug vacuum cleaners in to them and overload the circuit
3) As they were hard wired, the proprietor thought it would prevent the clientele stealing the lamps