Curious round 3 pin sockets in modern flat

Me and Mrs Midge were round at a friends flat this evening. Its a modern flat built around 5 years back and I suppose you'd say it was rather posh and well spec'ed.
Lounge/dining area has no less than two types of round 3 pin socket in addition to the normal 13A plugs and our friend was asking if I knew for certain what they were. One type is close to the pin spacing of a 13A, and has the same sort of shutter opener on the earth pin. I see from my Screwfix manual that some manufacturers have 5A round plug/socket listed so I assume its one of those and probably used for lighting - but what is the reasoning for putting them in such a modern property? I thought round pin sockets were old rather than new!
The other type of round pin socket is smaller. There is no shutter opener and my friend was once told it might be for surround sound system. This sorta ties in - there is one adjacent to the TV aerial socket, and sockets dotted around that end of the room where you might put speakers - but not knowing anything about such systems, I'd have assumed they would be individually cabled back to the TV so you'd have a row of them. I'll take a tool kit next time to have a proper look but any ideas on this one?
TIA, Midge
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wrote:

One possible reason for putting 3A (or was it 2A?) round-pin sockets in a room is so that peripheral lighting plugged into them can be controlled by a light-switch at the door. My parent's house was completely rewired with flat-pin 13A ring mains in the early 1960s, but in the main rooms there were also 3A plugs at floor level so that standard lamps and table lamps could be controlled by wall-switches. We hardly ever used the central-ceiling light.

Can't help with that except to suggest that the lack of shuttering suggests that it's not mains, so some sort of data connection such as you suggest is a possibility. Or are they composite video connections - if so they will consist of sets of 3 seperate 3mm sockets, one coloured yellow (video) and the other two red and white (stereo audio)? If they are CV, your friends probably wouldn't want to use them, as CV is an inferior quality video connection commonly associated with high levels of 'dot-crawl'.
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Thanks.
The idea of tying these sockets together to a master light switch does make perfect sense now you mention it. The lounge/dining room is pretty sizeable (over 30ft long) and lit with downlights, so you'd tend to have supplementary lighting (uplighters etc.) dotted around. Use of 3 pin round plugs would stop anyone putting anything heftier in them.
The smaller version is literally just that. At first glance you'd assume it was just a lower rated/smaller version of the same (I'll find out for certain when I'm next over there).
Midge.
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Round 3-pin come in 2A, 5A, 15A (and 30A, but not normally in a home). They are still permitted for use. If used in the home, shuttered versions are required. As stated, the 2A and 5A are commonly used for outlets powered from lighting circuits. The plugs are normally unfused, although fused versions have been produced (and I think still are by MK).
I have two 2A ones in my living room, used for a table lamp and display lighting built into a shelving unit, which run from the lighting circuit. (As with all my lighting, it's controlled by computer. It feels like the door switch controls it, but actually it just signals the computer and can be configured to anything I want.)
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Thanks Andrew - I'd assumed the smaller of the sockets was 2A initially but couldn't work out why you would have a 13A + 5A round + 2A round all in a line as there is on one wall. They are polished chrome finish too so don't exactly blend into the surroundings either!
Anyway, hopefully the mystery will be solved when I'm over that way again on Monday.
Midge.
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Bit of progress. The 5A sockets are all wired back to a wall switch (my friend had always wondered what it did!).
The smaller sockets are 2A. Blue/brown twin core mains cable but no earth (unless its somehow bonded across from the adjacent sockets. I was pretty sure I was going to find them wired up to the downlights, but nothing I switched on in the room got any of these sockets live. Checked the consumer unit and no breakers out. So they remain a mystery and we're putting a call into the management company to see if they know.
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wrote:

Where on the wall is the switch? Is it one of the light switches next to a door, or somewhere else? Are the sockets on their own circuit back at the consumer unit, or are they on one of the lighting circuits, probably the same circuit as the lights in the room?
I ask because IIRC lighting circuits are only rated at 5A, so a single socket rated at and consuming 5A could consume a circuit's entire rating without anything else being switched on. I would definitely have expected the 2A sockets, with or without switches of their own, to be the ones wired to a wall switch, probably next to a door, and the 5A to have their own switches and to be on their own circuit with higher rated cabling.

Are you saying that the sockets have earth sockets which are not connected to earth???????????????????????

I find this rather surprising! And, depending on the unknowns that I've questioned, possibly dangerous? I wonder if some cowboy electrician, young enough not to remember the round-pin 15A, 5A, and 2A circuits of yesteryear, miswired them?
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5A & 2A have earth pins, which must be earthed (it is not optional) which makes me wonder what "2-core cable" has been used? You can use flex, but the ends should be prepared accordingly to terminals not suited to flex (ie, bootlace ferrules).
Could be someone planned on 12V with remote transformer, hence the lack of an earth.
Either a bad requirements spec, or something trying to do "both" mains & 12V and ending up with an abomination :-)
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Had another look at the 2A last week - and its definately 2 core round flex (no earth) that has been used on that. So all I can assume is it was intended for some other (i.e. not mains) service. I've left this with my friend to quiz the management company for the flats.

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The 5A sockets go to a standard light switch. I haven't sorted out what is on what circuit on the consumer unit yet as I only had about 15 minutes to dig about. I agree, this doesn't feel right in any event as there are half a dozen of the 5A sockets around the room so the load could easily exceed the switch - even if they turn out to be on their own cct breaker.
All I can think of on the 2A is whether they were intended for something other than mains.
Hopefully I will get a bit more time to dig around next time I go.

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On 28/10/2010 22:21, Andrew Gabriel wrote:

I'll bite...
How does that lot work, then?
David
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