Round-pin sockets

pfraser brought next idea :

To switch a portable light, from a normal light switch, it is usual to use an uncommon plug and socket, to avoid someone plugging the likes of a vacuum cleaner into it - a 5amp socket fits the bill.

So does this circumstance qualify as an exemption from the normal rules (building regs?) that only square-pin sockets must be used?

I know that plugs in hard-to-reach places such as theatre lights high above a stage are allowed to use round-pin plugs because these do not have a fuse, so there's no chance of an inaccessible fuse blowing during a performance. I remember when I did the lighting for a school play being told that, and shown where the fuse-wire fuses for each circuit were placed: right above the fader for that light, so easy to reach in the semi-dark to replace if it happens mid-performance. There was a stack of pre-wired fuses available in case it happened. Obviously if the replacement fuse blows too, you give up!

Yes. When I built our conservatory, I fitted conventional 13A sockets for power and 5A, round-pin ones for additional lighting. So the 3-gang light switch switches ceiling lights; wall lights; and 5A sockets. We only normally use the 5A sockets for Christmas lights.

SteveW

I've not seen table lamps switched by a common wall switch in this country, but they were very common in the USA when I visited my sister while she was living there. And in that case they used normal power sockets which presumably were rated at the normal current for a socket in 120V-land.

Thanks Harry. That makes sense. My idle curiosity has been satisfied.

Pete

Parents' house built about 1900 had this.

It's just a convenience thing - no switching off the light from the doorway and then realising that you need to put it back on, go over to the table lamp, Christmas tree, etc. and switch each off and then turn the main light off again. Also means that at Christmas, we can turn the tree lights, fairy lights over the top of the window and lights on the wreath at the door on and later off with a single switch.

SteveW

It's also possible to attach a dimmer to that circuit so that a table lamp can be dimmed from a remote switch. Prevents someone attaching their phone charger to the circuit and it getting all confused by the choppy waveform.

(is there a modern way to do remote LED dimming these days, eg some kind of signal from the remote switch, or do they still do old-fashioned triac waveform chopping? Obviously there's some kind of RF signalling, but wondered if there's a standard protocol for wired lights)

Theo

Various proprietary and open systems, including DALI

Owain

I've got 4 x 5A sockets in the lounge for table lamps; they're on the 2 walls that don't have wall lights.

Owain

There is no such rule. BS546 (round pin plugs and sockets) is still a current standard. If you use them in domestic premises, it is now required that you use versions with shuttered sockets.

But I don't think BS372 are permitted.

NT

Agreed, from my years of living there. Very confusing the first time you try to get the standard lamp working, as there is no suggestion that it is controlled by a wall switch as well as its own switch. Hotels also confused by doing the same thing, and included the TV set in this mass switch-off. It then had to be re-programmed every time the room was entered, but this thankfully got better as the sets began to have memory built in.

It's common for anyone thatwants it. I have them myself for table lamps..

My school science labs were originally wired with them. They'd been repurposed into ELV supply for ripple tank lamps and similar.

BS 4573 plugs are.

See also

Owain

Not sure, but I too have seen some with shrouded pins just like the big ones with rectangular pins and a teeny 5 amp fuse inside. Maybe in reality it does not matter as long as its safe.

After all you seem to find all sorts of strange multi plug devices about nowadays with iec type plugs like thos on the back of computers, and I am not sure those are really supposed to be used in trailing sockets as the plugs have no fuses at all! Brian

You have it in one.

If that circuit had say a dimmer, and had a normal 13 amp outlet, there is the possibility of plugging in say a fan heater and blowing up the dimmer.

I've got several here. But fed from a dimmer on the same panel as other lights.

You need to be a lot more careful of your guests.