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Old 14th Dec 2012, 7:02 pm   #161
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Default Re: Another unusual plug and some other questions

Hi,

I have some old electrical books from the 30s or earlier and they often showed circuits with double pole fusing. I think the idea was that one fuse = good, two fuses = better. Therefore a fault would cause total isolation from the mains. Apparently, no one thought that one fuse might blow before t'other and the 50/50 possibility of the neutral fuse blowing first and thus rendering the faulty equipment still live!

I wonder how many fatalities it took before the penny finally dropped in later years and only the live conductor was then fused?

Cheers,
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Old 14th Dec 2012, 8:03 pm   #162
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Default Re: Another unusual plug and some other questions

Double-pole fusing was quite common - I grew up in a house built in 1959 which had double-pole fuses in the main fusebox. Everything - 5-amp circuits for upstairs/downstairs and outside lights, two 30-amp ring-mains, a 15-amp circuit for the immersion-heater, a 60-amp(!) circuit for the kitchen/scullery and a 30-amp feed to the garage/workshop - all were double-fused.

These were all on GEC porcelain rewireable fuse-carriers in four big metal-clad enclosures. We had a three-phase supply, and it was quite common in winter to lose a phase when a tree took out one or two of the overhead lines.
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Old 4th Jan 2013, 12:02 am   #163
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Default Re: Another unusual plug and some other questions

I'm assuming you all are familiar with the two different styles of Mk Bakelite plugs. I have recently acquired and restored what I assume is the older style (IE narrower than the usual MK ones seen) and slightly longer.

I think its cute with the way it has the red fuse size indicator in the centre screw which can be set to 3, 7 or 13!

At first I thought it was the same as the usual Bakelite MK's but comparing it to the one on my anglepoise it is narrower. Anyone know where it may date from?
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Old 4th Jan 2013, 12:17 am   #164
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Default Re: Another unusual plug and some other questions

Also thought this early attempt at safety sheathing by MK was ingenious (and overly complicated) And possibly extremely rare?
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Old 4th Jan 2013, 6:14 pm   #165
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Default Re: Another unusual plug and some other questions

Hi,

I've got one of those MK plugs with the spring loaded shields, so maybe not that rare, although yours is in better shape than mine!

Our council house was built in 1953 and had the earlier type with a screw for the live terminal (On the left of the photo). So, at least, early fifties. The later plugs had a nut and washer for the live terminal which made them easier to wire, but also made the body a little deeper.

When the red pointer under the cover screw was discontinued, the moulds were machined out which left the later plugs with a "bar" running across the centre as shown on the right of the photo.

The next photo shows a "Clix" stackable 13amp plug, and finally my favourite MK plug/socket combination (In dire need of a good clean and polish)

I really must get out more!
Cheers, Pete
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Old 8th Jan 2013, 4:22 pm   #166
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Default Re: Another unusual plug and some other questions

I love the combination - I need to find myself a double socket with backbox of that flavour to combine with my Anglepoise (which bears the later MK Brown Bakelite plug with wider flanges at the sides), whilst still allowing me to plug a laptop or such in - but its like looking for a needle in a heaystack, only very few seem to have survived and they seemt o be just singles!

Hmm glad to see you have a spring loaded one too. I would still imagine theres less of them kicking around, I dont suppose many of them actually remained working with those moving parts.

wHilst I have your attention, do you have any idea why the rivet for the fuse holder is always naked underneath?

And thanks for explaining about the line underneath - I had seen that before but never worked it out

As much as I love the MK design, I think early 50's would be too far backwards in time for my early 70's LEak Stereo 30 Plus...I think an Ever Ready would be more appropriate


Having said that I found & confiscated (for the obvious safety problem) a modern PVC cabled IEC lead at work today with an MK Ivory plug on it having had its premoulded one removed to get it through a hole in a workbench...its amazing that some every day people must have had these stashed so long in their tool box and still use them in a non-vintage environment as an on hand tool!
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Old 8th Jan 2013, 4:39 pm   #167
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Default Re: Another unusual plug and some other questions

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Originally Posted by unabridged View Post
wHilst I have your attention, do you have any idea why the rivet for the fuse holder is always naked underneath?
I've wondered that too.

The GEC 13-amp plugs I grew up with had the rivet to retain the fuse-clip, but the hole was packed with a yellowish semi-soft material which was something like wood-flour mixed with candle-wax.

The GEC plugs also had a little rubber protector fitted in a slot in the cable-exit hole: imagine a rectangle of rubberised canvas with a V-notch to allow the cable to exit. This only worked with thin cables (2-core flat or 'figure-of-8' twisted stuff for lamps etc) - anything thicker, like the cable for an iron or electric heater, led to the rubberised protector being discarded.

I guess GEC were more-than-obsessive about insulating things?

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Old 8th Jan 2013, 5:17 pm   #168
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Default Re: Another unusual plug and some other questions

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Originally Posted by unabridged View Post
Having said that I found & confiscated (for the obvious safety problem)
What safety problem? What they're designed for and as far as I know so long as they wired correctly perfectly safe and above board.

I think a 50's vintage plug on a 70's vintage equipment would not be an anachronism. Plugs were reused indefinitely until the era of the pre-moulded plug. Most replacement equipment would come without a plug and would have the plug off the equipment it replaced transferred to it.

Used to always be my job whenever we got anything new when I was a kid...quite a rare event though!
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Old 8th Jan 2013, 8:12 pm   #169
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Default Re: Another unusual plug and some other questions

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Originally Posted by unabridged View Post
Also thought this early attempt at safety sheathing by MK was ingenious (and overly complicated) And possibly extremely rare?
I'm sure I read somewhere (probably in a release when BS1363 was amended in 1987 to require sleeved L & N pins), that a sleeved pin plug was patented by Crabtree in 1967. Could this MK version with sprung shrouds be an attempt to avoid paying royalties to Crabtree?. In any case, MK introduced their "Safetyplug" with conventional sleeved pins around 1972 (I've got a 1972 MK catalogue and it's in there as the "new" Safetyplug).
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Old 8th Jan 2013, 11:47 pm   #170
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Default Re: Another unusual plug and some other questions

Surely if something becomes compulsory in law then any patent covering it would be annulled? Otherwise, one firm would have an unfair legal advantage, which would be tantamount to privatisation of the law.

Although, a 1967 patent would have run out by 1987 -- so maybe they just waited for it to expire and allow anybody to make sleeved plugs, before changing the regulations.
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Old 9th Jan 2013, 3:09 am   #171
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Default Re: Another unusual plug and some other questions

Plugs with part-insulated pins were available before the war, so the 1967 patent would have been to some particular detail of construction.

As regards standards, the last time I looked, the British Standards Institute stated in their literature that they would only consider incorporating something that is covered by a patent into a British Standard if the patent was irrevocably endorsed "Licence of Right", which means that the patent's owner would be obliged to grant a licence to any one who wants one on reasonable terms.
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Old 9th Jan 2013, 12:07 pm   #172
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Smile Re: Another unusual plug and some other questions

Hi,
Later MK plugs had a black plastic disc that covered the rivet for the fuse holder. This was often lost leaving the rivet exposed. I suppose the main risk was a flashover if the plug was used with a metalclad socket in humid conditions, but I've never heard of that. When the plugs with the larger finger shields were introduced, the disc was made from the same fibre material as the cord grip. Again, these would sometimes fall out.
The other photos show an Ashley plug with a fibre plate to obscure the entry hole when used with thin flex. These are often lost as well, so I suppose this brown example is a bit of a rarity.
I also have an MK leaflet which shows the standard plugs plus the "New SafetyPlug". It is shown with a fibre band & screw type cord grip instead of the later springy plastic "tongues" type of cord grip. I have never seen an early type, so wonder if it was ever sold?
Cheers, Pete
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Old 9th Jan 2013, 2:50 pm   #173
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Default Re: Another unusual plug and some other questions

I have seen a few of the rubberised ones shown in figure 4

But likewise have never seen the new style safety plug with screw terminals - wish they had made them as that would be much better in my opinion!

I wasn't aware MK made both the modern shethed style and the older shape at the same time.

I wonder when they stopped making the traditional shape then as shown in figure 1?

The only indication I ever got was that some of the Ivory/Bakelite ones had "Red,Black & Green" embossed inside by the relevant pins so presumably pre 1969, but some examples of the same shape and style did not have these colours embossed. Wonder how long that shape carried on.

I don't suppose I could get a high res scan of that MK catalogue perchance?
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Old 11th Jan 2013, 8:36 pm   #174
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Default Re: Another unusual plug and some other questions

Quote:
Originally Posted by unabridged View Post
Also thought this early attempt at safety sheathing by MK was ingenious (and overly complicated) And possibly extremely rare?
There's a few patents for MK plugs on Espacenet, as follows;

GB1067870 - This is the MK plug with the sprung pin shields in your photographs

GB1292991 - The standard sleeved pin plug

GB1269421 - A version of the Safetyplug cord grip, not quite the same as the ones we commonly see

I can't fing a Crabtree patent for a sleeved pin plug, so I'm wondering now whether I was right before regarding a 1967 Crabtree patent.
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Old 12th Jan 2013, 12:49 am   #175
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Default Re: Another unusual plug and some other questions

I couldn't find a Crabtree patent either. Perhaps they had a licence under someone else's patent. On the other hand, if the marking said "patent pending" or the like, then at that date, patents that were not granted were not published. It would be possible to find out if Crabtree had applied for any patents at that time, but this would involve personal inspection of the weekly Patent Office Journal at the SRIS in St Pancras, London, and the only details would be the title and the applicant's name.
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Old 26th Feb 2013, 1:15 pm   #176
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Default Re: Another unusual plug and some other questions

In my post of 7th Feb 2012 to this thread, I mentioned the use of 2A sockets wired to lighting circuits to give 'group switched' illumination of individual seating locations.

A recent visit to Chatsworth House revealed that a large number of their portraits are illuminated by individual fittings plugged into 2A sockets at high level, controlled in groups from 'normal' wall switch positions.

The sockets appear to be of 1950's / 60's vintage - some metal 'antique bronze' finish & some plastic and a number had 'multi adaptors' plugged in to feed more than 1 light fitting from each socket.
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Old 26th Feb 2013, 5:41 pm   #177
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Default Re: Another unusual plug and some other questions

Hi all although double pole fusing was abandoned here in the 1930s it is still commmon practice in Austria but only on single phase instalations 3 phase ones have a solid neutral link. although Austria now has the standard 220/380 volt supply system they have also had DC at various voltages and also 127/220 as described earlier in another post and even 150 volt supplies in rural areas.
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Old 14th Apr 2013, 10:33 am   #178
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Default Re: Another unusual plug and some other questions

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A recent visit to Chatsworth House revealed that a large number of their portraits are illuminated by individual fittings plugged into 2A sockets at high level, controlled in groups from 'normal' wall switch positions.
I work in a lot of old properties like that and it is very common to find lighting circuits with 2 amp sockets for ornamental or spot fittings. I believe it is also becoming more common in modern installations so as table lamps in living rooms can all be switched off at night by a second switch on the wall, according to my electrician friend.

A great idea in my books, but of course, what with you needing a degree and a written warning to the council to change a mains plug nowadays, I don't suppose it will catch on!
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Old 15th Apr 2013, 2:40 pm   #179
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Default Re: Another unusual plug and some other questions

I have a couple of those MK plugs on the left in post #168.
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Old 15th Apr 2013, 2:51 pm   #180
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Quote:
So if you ask a theatre electrician for a 15A grelco, he will probably hand you a 16A Snapper
I still call adapters "Grelcos", by way of a hangover from a mis-spent youth dabbling as a semi-pro theatre technician.
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