Strange Grelco adaptor... a question for the 'vintage' sparkies

[Lucien Nunes]

I'm not usually stuck for ideas about old plugs but this is a new one on me.

See pics...



It's just like a regular 2-pin 5A Grelco, except for that peg leg in the middle. The middle holes in the sockety ends don't contain any contacts. The L&N pins are normal 5A gauge and centres.

What would it fit and why?

 

[overskilled]

old UK to Italian / Swiss? Other option for the plug end / male end...IEC60906?

 

[Lucien Nunes]

I agree it looks superficially like Italian but it wouldn't fit, the pin centres and diameters match British 5A 2-pin (BS372/1) not the 19mm/4mm that is common to all the European flavours including Italian CEI23/16. Also I don't recall ever seeing a Grelco brand adaptor to fit a non-UK standard.

Oddly, the centre holes in the sockets wouldn't accept a pin the same size as the one fitted. It's not used a contact, so could be for opening shutters, operating a switch or preventing the plug being inserted into an ordinary 5A socket. IIRC Agro sold a plug (maybe for bell systems) with three pins in a line, the middle one being thinner, but from memory the outer pins weren't 5A gauge.

 

[Marvo]

I'm not certain but my first thoughts were stage plugs. Maybe it's a audio/sound plug and the centre pin prevents it being plugged into electrical sockets. Maybe it is electrical and the pin is to make it more stackable for stage lighting. I don't think the centre pin was ever intended as CPC because it's shorter than the L&N pins. I also thought at first it might be to ensure correct polarity but it looks like it's dead central so that wouldn't work.

 

[Rockingit]

I'm not certain but my first thoughts were stage plugs. Maybe it's a audio/sound plug and the centre pin prevents it being plugged into electrical sockets.

It's not one of ours! Although, that being said, there are still a whole heap of non-standard plugs and splits made for hooking up lighting - you'll find them in the RS catalogue - occasionally you'll run into some in the exhibition world. It might just be some fore-runner of something now made in plastic.

 

[Lucien Nunes]

There are some stage connectors with three round pins approximately in a line. The Americans still use a series of sizes generically called 'stage pin'. We used to have two versions in the UK, one with the earth pin at the end based on 15A gauge that we called '3-in-line' and another with the earth in the middle offset to one side like IEC60906, made only by Major. All of these are larger than my mystery adaptor.

We also used 2-pin plugs for audio, especially 100V line speakers, but they had different pin centres and diameter. The only things that usually had the 5A gauge pins were inline flex connectors, in 2 and 3-pin versions, but the 3-pin jobs had a real third earth pin. This adaptor doesn't use the pin as a contact and can't accept a plug with the same kind of pin, so it's unclear what function it would have had on the plug.

Grelco adaptors were popular in the UK. In the theatre a 2-way 5A or 15A 3-pin adaptor is still called a 'Grelco' (or sometimes a 'Snapper' after the SA brand that we import). I have got dozens of Grelcos for 2A, 5A and 15A 2 and 3 pin, with many combination of sockets, but this is the first one I've seen with this extra pin.

 

[peterb]

Hello, I think these were used at lower voltages and the extra pin was to prevent the plug being inserted in a normal 230V socket (or 240V as it was).

I have seen them on old 12/24/36 V electric blankets but not for 40 years !! These used to have a heavy transformer control box and were rated at about 200W. I shudder to think about the consequences of plugging one into a 230V socket.

 

[DPG]

The consequences would be a much warmer bed. Daz

 

[Marvo]

It's not one of ours! ...

Well if it's not a stage plug format I'm stumped. It does look like it's specifically designed to be stacked and I still think the centre pin may have been to add some stability when there's several plugged together. It could even been a proprietary format that was used only by a specific manufacturer on their own equipment in which case good luck in identifying it.

Where did you come across then Lucien?

 

[overskilled]

Haven't located it yet....even foiled google image search...though turned up the following monstrosity....

 

[Marvo]

I'm not even going to ask what on earth that lead is in aid of.

 

[overskilled]

Socapex Breakout Spider - 15Amp Plugtop

Thats a link to the page....if the cores are wholly separated it isn't as bad as first seems...but still an electrocution waiting to happen......

 

[Lucien Nunes]

That's a bog standard bit of UK stage kit, I've probably got a dozen in the shed and a dozen of the opposite gender, must have made hundreds of them over the years. The 19-pin 'Socapex' connector mates to an 18-core YY flex with Socapex both ends, to carry six electrically separate 15A 3-core circuits. So you might have a row of Socapex outlets along the front of your dimmer rack, run the circuits up in sixes to the truss and then break them out with socket spiders or breakout boxes, or you can use that plug spider to collect six circuits from different places and send them all up one Soca cable.

Re the Grelco:

It does look like it's specifically designed to be stacked

But it won't stack, the centre holes are smaller than the centre pin. So if the socket fits the plugs, the adaptor won't fit the socket!

 

[happysteve]

Scarily, you can use soccy for speakers too, and some do. So you get the situation where you're trying to work out which cables are connected to which bars... Plug one into a dimmer. "Dave, I'm gonna flash out channel 1 on this one that's not marked up, can you have a look see where it is?" *bang* "What was that?!"

"Dunno."

...

"Try channel 2..."

 

[snowhead]

Right, got the answer,,, nearly.

The middle pin is to STOP the splitters / adapters being stacked in an endless pile and having 10's of plugs loaded up on 1 circuit.

What I can't explain, having not seen these before, is how the 3rd pin fits into the original fixed socket.

It's mentioned on this group near the end; https://groups.google.com/forum/#!topic/rec.arts.theatre.stagecraft/4PK8bN5F07A

 

[Lucien Nunes]

*bang* "What was that?!"

Not guilty! Well, except maybe once at the CNIT in Paris although strictly speaking I didn't plug them in myself. But we had more to worry about than a couple of smoking cabs. The best bangs I've had out of Soca was on a outdoor show that was packed down in the rain and left shut in the trucks for 2 weeks, then built up and plugged straight in. One day I'll tell some stories about that one, was in Russia, had some interesting 'challenges'.

E2A Snowhead I haven't read all of that thread but it's mostly about the USA stage pins, where the regs are quite different from anything that ever applied to BS372 round-pin UK plugs. The theory of making it non-stackable is interesting, you have a large hole in the socket and a small pin on the plug, so that you can put plugs and adaptors into sockets, and plugs into adaptors, but you can't put adaptors into other adaptors. This is a bit like the Wylex plug where you can stack 5A into 15A but not 15A into 15A. But as you say, what kind of socket?