Connectors - and ring mains

[charles]

Yes

[Harry Bloomfield, Esq.]

Yep, I used to have one, wired to a 13amp socket - in the days when you were faced with a variety of plugs.

[Brian Gaff (Sofa]

Well Europe seems to be a mess of different plugs and ad hoc installed extra bits all over the place. I bet there are standards, but whether there is compliance is a whole other thing.

Brian

[Brian Gaff (Sofa]

Might I just say that although this house was built in 1939, it was built using 13 amp sockets on the old rubber and fabric covered wires, including earth. I could not say if it was ring main or not, or much else but I can tell you that the lights did not have unstitched lives in the rose. There were also a smattering of 2 pin 5a sockets as well, apparently wired to the one lighting circuit. All the 13 amp sockets were on one circuit. Of course the old consumer unit used wire fuses, and was made of metal.

We had the place rewired in the 70s and then we had split upstairs and downstairs circuits, all the sockets were raised up above the skirting and all were on ring mains, but oddly, the bar fires in the bedrooms were on the lighting circuit, not the socket one. In one case it was spurred off the ring though as it was basically an afterthought.

Apart from the colours being wrong for today and the old circuit breakers instead of the more sophisticated fault protection of today, its in very good condition still. Brian

[Tricky Dicky]

How about these,

A flat I moved into in the early seventies had sockets for these, the plugs were a bugger to find. I think the landlord used them deliberately and sold spares to tenants to enable them to cob together leads in order to use standard square pin plugs on personal electrical equipment. I think he limited the number issued so the system could not be overloaded.

Richard

[charles]

They look very much like the ones the NSHEB introduced. The D&S mentioned on that page were adopted at TV Centre for 'technical supplies"; stopped the cleaner plugging in a vacuum cleaner. They were probably used in some mansion blocks in central London since Selfridges used to sell the fuses.

[Owain Lastname]

There was also the thread "Unfused 13A plugs on mobile X-ray machines", Mon, Jul 21, 2014 8:58 AM

Owain

[Owain Lastname]

1. Because they didn't have 2A and 5A circuits, their appliances had thicker flexes?
2. Many European countries had bottle fuses which may have provided finer protection than rewireable fuses used in Britain.
3. Their electrical safety standards were/are lower?
4. We designed the fused 13A plug to suit the conditions in the UK at the time and to be the best possible solution overall, albeit a compromise in some ways.

Owain

[Max Demian]

I would have thought it would be better to have fused sockets, then there wouldn't be the chance of overload with multiple appliances plugged into the socket with an unfused adapter.

[Max Demian]

Yes they were yummy.

[Theo]

The circuit breaker (or rewireable fuse) is supposed to protect the house wiring. The plugtop fuse is to protect the appliance wiring. A fused socket can't tell whether you plugged in a 1A appliance or a 13A appliance. If the 1A appliance starts taking 10A its cable may melt, but a 13A fused socket wouldn't notice. By putting a 1A fuse in the plugtop you can protect the appliance's cable.

If you're running a multiway extension then that has a fuse in /its/ plugtop which is matched to the maximum current the extension can handle. If you daisy chain extensions, or plug in three kettles, that fuse should blow before troubling the circuit breaker. There shouldn't be unfused adapters, because then you're only relying on the circuit breaker.

If you have a removable appliance cable, like a C13 'kettle lead', the same holds if the fuse in the plugtop is rated for the size of the cable - it's fine to fit a 10A fuse on a C13 cable capable of carrying 10A - as long as the appliance has its own fuse (typically at the IEC inlet) rated for its own requirements.

Theo

[Dave Plowman (News]

Err, theatre lighting doesn't use a ring main. Most usually a radial with dimmer control. You don't want such circuits confused with a GP mains supply - hence different connectors.

[Dave Plowman (News]

Pretty certain 13 amp was a post war thing, Brian. But it could have taken a long time to build your house. ;-)

[Dave Plowman (News]

How would the socket know which fuse to fit? Never noticed some appliances come with a 5 amp fuse in the plug?

[NY]

Ah, I wasn't sure whether lighting circuits in theatres were spurs (with only one route from the supply to the lamps) or a ring (with two alternative routes from the supply to the lamps). Either way, they are fused at the lighting board rather than the plug, and usually the supply goes via a variable resistor or triac dimmer and switches so several circuits can be switched on/off or dimmed in synchrony.

I remember working as a lighting operator for school plays, perched 10 feet above one side of the stage on a gantry with a row of about 10 vertical wire-wound dimmers which could be switched between lighting circuits - eg we'd put all the lights that we wanted to dim in sync on adjacent dimmers so a 2-, 3- or 4-dimmer length of wood could be used to move all the dimmers in sync. Once that effect was over, we'd switch circuits to other dimmers to put ones for another synchronous effect on adjacent dimmers. The fuses were per dimmer rather than per lighting circuit, so if a fuse blew, you switched the circuit to another dimmer while you rewired the blown fuse. I remember the "blackout" switch that killed all lights everywhere when a total instantaneous blackout was needed: it was a surprisingly small insignificant switch which operated a humungous relay nearby which always made a loud clonk.

The big daddy dimmer was the one for the house lights. That was a flat box about 3 feet square with load of ventilation holes all over it and a big wheel on the front that made a loud screeching noise as the contacts moved over the wire-wound coil. The instruction there was the move it smoothly, quickly and fully from one end to the other, not leaving it half-on or almost-but-not-quite off/on for any longer than necessary because it got very hot. I think there were 24 house lights, each with a 500 W bulb shaped like a very large 60 W bulb, so that was 12 kW that had to be dimmed - hence the need to go from off to on as quickly as possible, because the wire-wound coil didn't like 12 kW passed through it.

The school also had a lecture theatre with a modern triac dimmer system in the projection booth and ceiling-mounted lights. But it had no proscenium arch and no wings, so all the fancy lighting couldn't be used for a stage play where actors had to enter or exit. The only way to do it was to open one of the fire doors either side of the "stage" and have the actors enter from outside in the playground.

What intrigued me about the lecture theatre was that the fluorescent tubes could be dimmed from very dim to fully bright - they couldn't dim right to extinction so there was a sudden switch-off once they got very dim. But I'm not sure how you dim fluorescents while maintaining the striking voltage. Did they feed them with a crude square wave that remained above the striking voltage for an gradually-decreasing portion of each mains cycle, a bit like you'd dim LEDs?

[charles]

yes, but the reason is you don't want a fuse in some remote part of the rig.

[Roger Hayter]

How has it come about that electricity plugs are called "plug tops" and electricity sockets are called "plug sockets"? There seems to be no ambiguity using just "plugs" and "sockets".

[S Viemeister]

I have wondered about that. Makes no sense to me, at all.

[Theo]

Plug top v plug bottom :-)

Theo

[Robin]

the story I recall is that it dates from the early days when electrical connections one could make and break were novel and were sold as plug points, each of which comprised the bit you pushed in (the plug top) and the bit you pushed it into (the plug socket). And I think this was before the days of sockets on domestic walls.