Another socket puzzle: Why the extra terminal?

[Lucien Nunes]

Here's an old accessory made to BS1363. You can connect it to a ring and plug 13A plugs into it. What is the fourth terminal for?

I've blanked off some text moulded into the bakelite so as not to give too many hints at first. Nothing else is hidden.

 

[Michael Sands]

You need to stop biting your fingernails

 

[littlespark]

Some form of switch?
The socket is energised only when there’s power to that terminal, lower current than the ring?

Just a guess

 

[Timbo]

Is that a fused output?

 

[Lucien Nunes]

Yes. What for?

 

[Spoon]

lower current than the ring?

You might be onto something there, as the cable hole size is smaller than the others..

 

[SJD]

Fused output for e.g. a round pin lighting socket?

 

[Toneyz]

I was going to go for clean earth?

 

[littlespark]

Ah... 13a socket and a 5 amp on the same plate... for all the old lamps that people had plugged in

 

[Lucien Nunes]

Fused output for e.g. a round pin lighting socket

Surely the point of BS1363 was that all appliances had the same plug, eliminating other kinds of socket? A lighting point controlled by a wall switch, fed by the lighting circuit, might reasonably use a round pin socket to avoid other appliances being connected. But this is off the ring, so why not use more 13A sockets?

 

[Pete999]

I was going to go for clean earth?

What's a a clean earth?

 

[littlespark]

What's a a clean earth?

One with no polluting human beings on it

 

[telectrix]

deleted, need more beer.

 

[Pete999]

Some form of switch?
The socket is energised only when there’s power to that terminal, lower current than the ring?

Just a guess

Show us the front then.

 

[Lucien Nunes]

You need to stop biting your fingernails

I ripped chunks off both thumbnails ages ago using them as emergency screwdrivers, but my hands have taken such a beating with working round the clock for months that all my finger tips are basically worn through the skin and the nails worn and split. I was even contemplating wearing gloves which I hate!

 

[Lucien Nunes]

Front. So what's the terminal for?

 

[SJD]

So maybe a fused output for something you wouldn't need to plug/unplug, but is hard wired in - e.g. a doorbell?

 

[Pete999]

Front. So what's the terminal for?

View attachment 47708

Fused supply for the 5 Amp sockets, get a grip.

 

[SJD]

Aah, I was thinking "fireside" socket but no idea why it would need an extra terminal, unless for something to be hard wired in.

 

[telectrix]

the 4th terminal is a fused L for 5A round pin socket/s.

 

[Lucien Nunes]

Fused supply for the 5 Amp sockets, get a grip

They're 2A, and the fuse is built-in.

 

[Pete999]

the 4th terminal is a fused L for 5A round pin socket/s.

What I said except get a grip. Not you Tel

 

[Lucien Nunes]

Why would you want to cater for 2A sockets when installing a ring?

 

[Pete999]

the 4th terminal is a fused L for 5A round pin socket/s.

Still not many 5 Week wonder DI courses have seen this sort of thing have they?

 

[SJD]

The valve radio, or the table lamp.

 

[Pete999]

The valve radio, or the table lamp.

What is that supposed to signify SJD?

 

[Toneyz]

The terminal is not shrouded like the rest. It appeared to be the size of a single socket in the first picture.

 

[SJD]

My comment was in reply to Lucien's question just above as to what you would use the 2A sockets for!

 

[Pete999]

Table or standard lamps as was the norm in those days, 50s 60s 70s maybe long before people decided to change careers

 

[Lucien Nunes]

The fourth terminal is indeed an output sharing the onboard fuse protecting the 2A sockets. It's intended for the rarely-seen companion unit containing a further four 2A sockets. The combination appears on the ring as one double point (one 13A socket and one unswitched FCU) but gives a total of seven sockets in two accessories. Heater, clock, lamp, TV, radiogram, other lamp, train set, spare, or whatever.

Never caught on, presumably as it defeated the idea of all plugs being identical and hence interchangeable.

 

[The Ghost]

Kept meaning to show you this @Lucien Nunes to see if it is of interest for your museum. Took it out of my house while doing a few changes.

 

[Toneyz]

So it doesn't fit in a standard single k.o. box?

 

[littlespark]

Interesting piece of history there... never seen something like that before.
My gran had an adaptor from 13a plug to 2x15a + 1x 5a, so they could still use their old appliances without changing the plug.

 

[Lucien Nunes]

So it doesn't fit in a standard single k.o. box?

No, it's a custom size.

Kept meaning to show you this

Is that Bath - Off - Sink for a dual element immersion? Yes please, we don't have any of those. Will happily pay postage! Pity the red indicator lens is missing but we can find something suitable.

A side note about the fireside socket fuse. The original design shown here takes a BS646 fuse so the largest you could fit was 5A, which was correct for multiple 2A sockets on one circuit. But the later style in a standard 2G plate took a BS1362 fuse so a 13A fuse could be fitted leaving the sockets poorly protected. But in practice, unless the wrong appliances were connected to 2A plugs, due to a lack of 13A sockets, it was unlikely to cause serious hazard.

 

[freddo]

Pity the red indicator lens is missing but we can find something suitable.

The last one of those I saw (sadly still in use so I couldn't pinch it!) had a neon bulb in it which slightly protruded through the front hole.

 

[The Ghost]

s that Bath - Off - Sink for a dual element immersion?

Yes indeed thought it might have had a red bulb in it. Just tell me where to send it no postage required.

 

[Lucien Nunes]

Ah, maybe that's it. I thought Santon used a domed red lens but perhaps that was someone else. In that case I think we have the correct neon.

 

[KEV 1 N]

Found this the other week in an old boiler house...

 

[Toneyz]

Found this the other week in an old boiler house...
View attachment 47719 View attachment 47720 View attachment 47721

Non of this digital rubbish then!

 

[Lucien Nunes]

Fun! Outdoor compensation thermostat or some such, I'll take a closer look later.