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

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Lucien Nunes

Lucien Nunes

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

See pics...

[ElectriciansForums.net] Strange Grelco adaptor... a question for the 'vintage' sparkies[ElectriciansForums.net] Strange Grelco adaptor... a question for the 'vintage' sparkies

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?
 
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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.
 
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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.
 
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Marvo said:
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.
Click to expand...

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.
 
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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.
 
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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.
 
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Rockingit said:
It's not one of ours! ...
Click to expand...

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?
 
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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
Click to expand...
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!
 
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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..."
 
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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
 
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