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Old 9th Feb 2012, 5:49 pm   #81
hannahs radios
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Default Re: Another unusual plug and some other questions

Hi.

I can remember when I was in Brompton hospital in London in about 1979 the sockets for the portable X-ray machines looked like they were 30 amp round pin jobs. They definitely seemed larger than the 15 amp type we had at home. The hospital seemed to be in the middle of a rewire at that time.
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Old 15th Feb 2012, 12:11 pm   #82
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Default Re: Another unusual plug and some other questions

Interesting to read the price list for lamps in 1893. In 1993 I was selling standard lamps in my shop for around the same price. Must have been the bargain of the 20th century!
The simple lamp, so taken for granted like so many things today. Cheers, John.
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Old 17th Feb 2012, 1:22 am   #83
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Default Re: Another unusual plug and some other questions

In 1893 the lamps were still hand made and used platinum for the lead-in wires, DUMET not having been invented then.

The complexity in manufacture is apparent from the following item from the Model Engineer for 1904.

In the evening of Monday November 7th. a party of twenty-six members paid a visit to Messrs. Robertson’s Incandescent Electric Lamp Works at Hammersmith. The party were met by Mr. Robertson and conducted in two groups over the whole of the very extensive factory, every detail of the production of Robertson electric lamps being shown and explained, the members thus having an opportunity of watching the growth of a complete lamp through the thirty-seven different stages, including the manufacture of the raw filament, drying, carbonising, fitting the platinum entering wires, flashing, sealing in bulbs, exhausting capping, grading the candle-power by photometer, testing and packing, &c. The extreme care taken to ensure efficiency in every stage of manufacture and the multiplicity of tests applied much impressed the party, and at the close of what was considered to be one of the most interesting and instructive visits made during the past year, the hearty thanks of the party, was tendered to Messrs. Robertson and Wilson and their assistants for the way in which they had arranged for the entertainment of the visitors.

[The Model Engineer and Electrician, December 1, 1904 page 506]


In 1904 Henry Loring of the Robertson lamp works wrote a book entitled "From the beginning", profusely illustrated with photos, that explained all of the 37 stages referred to. I had read, and made an indifferent photocopy of, the volume that used to be in the GEC archives, but the IET library has a copy. "Flashing " involved the female operative immersing the filament in liquid benzene and energising it so that it glowed under the liquid, causing disassociation of the Benzene so as to deposit carbon on any hot spots, thereby making the filament more uniform.

Nasty stuff, Benzene. In the 1970's we were testing our PLL receiver boards immersed in Benzine as it has about the same dielectric constant as the Araldite that we were using to encapsulate the finished product [someone had borrowed a gallon of the stuff from the chemistry lab downstairs]. I mentioned this over a game of cards to one of my friends who was an industrial chemist and he nearly fell off his chair. After he sent me the safety sheet [progressive irreversible brain damage from inhaling fumes: known carcenogen; nothing greater than 250ml to be used outside a fume cupboard] the Benzene went back to the chemistry lab forthwith!
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Old 18th Feb 2012, 4:34 pm   #84
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Default Re: Another unusual plug and some other questions

Many years ago I bought a few NOS 13A plugs & matching sockets (from Proops, probably...). Made by MK, with silver-plated blades. I used a couple to add switched mains out to the back of an amplifier. The plug contains a standard BS mains fuse.

John
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Old 18th Feb 2012, 9:05 pm   #85
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Smile Re: Another unusual plug and some other questions

Hi,
I wonder if they were designed for some system of connecting factory lighting to overhead trunking? I'm sure I've seen something vaguely similar. That design no. might lead to some info. The tarnishing on the pins hints at an industrial atmosphere.
Cheers, Pete
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Old 18th Feb 2012, 9:09 pm   #86
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Default Re: Another unusual plug and some other questions

Could well be, as the socket would fit in a simple rectangular cut-out and it was very slim/compact.

John
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Old 18th Feb 2012, 9:22 pm   #87
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Default Re: Another unusual plug and some other questions

I think I vaguely recall some sort of track system which these worked with.
Sockets which could be slid onto the track and locked in any desired position?
Perhaps I'm thinking of something else entirely!
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Old 18th Feb 2012, 10:19 pm   #88
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Smile Re: Another unusual plug and some other questions

Hi,
That sounds reasonable as some trunking systems used solid busbars that the sockets clipped on to after removing a blanking plate every few feet.
Hm, curiouser and curiouser.
Cheers, Pete
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Old 18th Feb 2012, 11:54 pm   #89
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Default Re: Another unusual plug and some other questions

IIRC the opposite side of the plug states 'Non Standard', implying they were variant mains outlets for special application supplies.

Lucien
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Old 19th Feb 2012, 4:26 pm   #90
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Default Re: Another unusual plug and some other questions

Quote:
the opposite side of the plug states 'Non Standard'
Spot-on!

John
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Old 4th Mar 2012, 3:44 pm   #91
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Default Re: Another unusual plug and some other questions

Hello, today my grandmother found a load of old plugs, among them were these three odd ones. The first two are Crabtree 5A round pin plugs but with notches on the earth pins. They are basically the same with the same numbers, but one plug has one notch the other two. I assume they are there as part of an interlocking arrangement?

The third item is a round pin to bayonet adaptor, made by GEC. The movable pins allow the adaptor to be plugged into a 2, 5 or 15A socket. The outlet side has a sprung plate which sort of prevents accidental contact with the pins.

There was also a 5A MK plug which is identical to the current production MK plugs (except this one is brown).
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Old 4th Mar 2012, 3:51 pm   #92
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Default Re: Another unusual plug and some other questions

I believe they were designed to go with special switched sockets that only allowed a plug to be inserted or withdrawn with the switch off (perhaps for DC use?) A restrictor plate clamped the earth pin while the switch was on, and also prevented the insertion of a plug in that state (but in case anyone tried, the live pins were partly sleeved so the portion sticking out of the socket would be safe).
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Old 4th Mar 2012, 4:11 pm   #93
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Default Re: Another unusual plug and some other questions

Here is another odd one I came across during a test and inspect. It is a large 30A round pin plug with locking ring. It's difficult to see in the photo due to the years of dirt, but the large plug body and ring are made of brass. I can't remember a brand name. It was certainly industrial and heavy. It certainly looks like a Lewden industrial plug, perhaps an earlier version. The newer ones are made of cast aluminium I think.

Matty
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Old 4th Mar 2012, 8:26 pm   #94
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Default Re: Another unusual plug and some other questions

I had one of the 5 amp 3 pin plugs, and mating socket, of the type shown in Matthewhouse's picture - they used to belong to one of my great Aunt's who owned a business in a small mining village so suspect that these may have been intended to be used on DC supplies at some time.

The Earth pin did indeed operate a latch mechanism in the socket which prevented the socket being switched on with no plug inserted and, conversely prevented the plug being withdrawn from the socket once the switch was in the 'ON' position.

The plug and socket were lost in a house move many years ago but from memory the pins had the same dimensions as a BS546 5 amp plug (although I may be incorrect) which suggests that the socket may not have been designed for DC use, as a standard non - latching plug could have also mated with it; I do seem to think that the switch assembly, in the socket, was of the "blade and fork type" though which was suitable for DC use.

Andrew
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Old 4th Mar 2012, 9:03 pm   #95
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Default Re: Another unusual plug and some other questions

Out of interest the Lewden screw locking industrial plugs are still available, although rarely seen these days, presumably due to the very high price compared with the BS4343/IEC60309 plastic "CEEform" types. http://www.tlc-direct.co.uk/Products...30slash3P.html
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Old 4th Mar 2012, 9:40 pm   #96
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Default Re: Another unusual plug and some other questions

They are very expensive, I fitted a plug recently. The three phase ones have pins that are rather exposed!
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Old 5th Mar 2012, 12:09 pm   #97
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Smile Re: Another unusual plug and some other questions

Hi,
Somewhere here I've got a couple of those 5amp Crabtree plugs with a groove around the earth pin. It is indeed an interlock and works well.
But.
The earth pin, you'll notice, is also hollow because the mating socket has a rod in the earth hole with a sliding spring loaded disc that blocks the latch & the switch from moving when no plug is present. Insert a plug and the disc is pushed down by the pin. The groove then coincides with the latch and the switch can thus be operated and the plug trapped.
There were two snags with this design:
1. Only Crabtree plugs could be used as only they had hollow earth pins.
2. W&G used to make sockets with shutters that twisted sideways when a plug was inserted. OK with ungrooved earth pins, but grooved Crabtree plugs would get stuck and could not be removed. I know, 'cos I've done it!
Cheers, Pete
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Old 5th Mar 2012, 5:13 pm   #98
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Default Re: Another unusual plug and some other questions

Quote:
1. Only Crabtree plugs could be used as only they had hollow earth pins.
Not a snag for Crabtree!
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Old 5th Mar 2012, 7:08 pm   #99
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Default Re: Another unusual plug and some other questions

I did wonder why the earth pin was hollow. I guess it ensures that non interlocked plugs can't be used, a safety feature!
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Old 5th Mar 2012, 7:17 pm   #100
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Smile Re: Another unusual plug and some other questions

Hi,
Possibly, or clever marketing as the householder had to buy Crabtree plugs! I don't think it lasted long as I've got another socket of the same age which does not have the central rod and will accept any make of plug. Either it was a later version, or the interlock feature was a "with or without" option.
Cheers, Pete
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