Plug sockets

[Tractorfan]

Hi,
Hm. Now isn't that odd. The one I have isn't flush as the 'plug' projects quite a bit from the plate which, in itself, is very slightly domed. Plus, there's no provision for hanging anything.
The plot thickens.
Cheers, Pete.

[johnpriceuk]

Absolutely love the massive metal clad cooker switch from the article in post #55!!!!

[Tractorfan]

Hi,
I was helping one of my wife's friends to clear out her late father's garage and there was a vintage cooker switch/socket amongst all the junk. I think it was a blue speckled enamel finish on cast iron and had a 5amp socket. I put it to one side to take home the next day, but in the meantime her sister found it and pitched it in the skip!
Cheers, Pete.

[emeritus]

The article and pictures featuring MK attached to post #55 was interesting, but some of the information may be slightly misleading.

The brown switched 13A socket was evidently an early model as its fixing screw holes are arranged vertically rather than horizontally. However, it must date from the 1950's as the original BS1363 specification did not allow switched sockets. Possibly this was because there were still significant pockets of public DC mains in the 1940's and early 1950's?

As has been mentioned in another thread, plugs with partially insulated pins were certainly available by the 1930's: I have an old 5A 3 pin plug myself (made by "Contact") in which the insulating sleeve has clearly been moulded in place over the reduced diameter portion of each pin (including the earth in my example). The distinctive feature of the MK patent that is mentioned (evidently GB1292991, filed 7th April 1970, but not published until 18 Oct 1972) is a discrete sleeve that is fitted to the plug pin during assembly, and is clearly much easier to manufacture than the pre-war moulded-on designs.

Lundberg had patented a polarised 3 pin plug having a similar configuration to BS 456 plugs as early as 1906 (GB 21390/1906). It was for use with 3-core flex and a special socket having a 2-way switch, and was for use with a portable appliance (such as a table lamp) also having a 2-way switch, so that the appliance could be independently switched on and off either from the wall socket or the appliance itself. Thus all three pins were used for carrying current, although only two would actually be carrying current at any given time that the appliance was switched on. Possibly it was realised that it could be used as an earthed connector when earthed domestic supplies were subsequently introduced. The GEC catalogue of 1910 includes some non-polarised earthed industrial plugs and sockets having three round pins, but the pins were all in line like Italian mains plugs, and the plugs were therefore reversible.

[Socketman]

Originally Posted by emeritus

The article and pictures featuring MK attached to post #55 was interesting, but some of the information may be slightly misleading.

The brown switched 13A socket was evidently an early model as its fixing screw holes are arranged vertically rather than horizontally. However, it must date from the 1950's as the original BS1363 specification did not allow switched sockets. Possibly this was because there were still significant pockets of public DC mains in the 1940's and early 1950's?

The requirements for what became BS 1363 were first published in Post-War Building Studies No. 11. (Incidentally, the PWBS series was initiated by Lord Reith as Minister, but he was not, as stated in the MK article, the chairman! For PWBS 11 the chairman was J R Beard.) As far as switches go, what PWBS 11 said was: "On A.C. circuits, which we have assumed will be universal in new buildings, disconnection can be safely made by withdrawing the plug; the expense and complication of a separate switch is therefore unnecessary in the standard design. It may, however, be desirable to have an alternative standard design incorporating a switch for use where this additional convenience is required." Hence, when BS 1363 was published in 1947, there was no option for a switch. The original title of the standard, "Fused-Plugs and Shuttered Socket-Outlets" was changed in 1950 to "Specification for two-pole and earthing-pin fused-plugs and shuttered socket-outlets for A.C. circuits up to 250 Volts (not intended for use on D.C. circuits)" which makes the no DC usage even clearer. However, the British public had grown used to the convenience of switched sockets (and were probably unaware that the purpose of the switch was to prevent arcing) so there appears to have been a demand for sockets equipped with switches. As this was long before the days of the Plugs and Sockets Regulations there was nothing to prevent the sale of non-standard plugs and sockets, and many, including D&S and Wylex types, were on the market at the same time as BS 1363 and BS 546. In 1957 the "alternative standard design" foreseen by PWBS 11 became standardized as BS 2814:1957 "Two-pole and earthing-pin flush-mounted 13-Amp switch socket-outlets for A.C. circuits up to 250 Volts" and it was not until BS 1363:1967 "Specification for 13A plugs, switched and unswitched socket-outlets and boxes" that switched sockets were incorporated into BS 1363 itself. Early switched 13A sockets were therefore not marked as being to BS 1363, as illustrated by the attached images of a double switched socket, but the BS 1363 marking is clear on the early (vertical fixing holes) MK non-switched socket. The later (horizontal fixing holes) MK switched socket is clearly marked BS 2814.

Originally Posted by emeritus

..... As has been mentioned in another thread, plugs with partially insulated pins were certainly available by the 1930's: I have an old 5A 3 pin plug myself (made by "Contact") in which the insulating sleeve has clearly been moulded in place over the reduced diameter portion of each pin (including the earth in my example). The distinctive feature of the MK patent that is mentioned (evidently GB1292991, filed 7th April 1970, but not published until 18 Oct 1972) is a discrete sleeve that is fitted to the plug pin during assembly, and is clearly much easier to manufacture than the pre-war moulded-on designs.

I too have a number of older 5A and 15A plugs with sleeved pins, some where the sleeves appear to be in the same brown material as the plug body, and others where they are coloured red and black. I am unsure about the age of these, and it would be great to see some reference to sleeved plugs in old catalogues or literature. By the way, an earlier method of sleeving flat pins is contained in the MK patent GB1067870 filed in 1963, this uses sprung loaded plastic sleeves which are pressed back into the body of the plug as the pins enter the the socket.

Originally Posted by emeritus

..... Lundberg had patented a polarised 3 pin plug having a similar configuration to BS 456 plugs as early as 1906 (GB 21390/1906). It was for use with 3-core flex and a special socket having a 2-way switch, and was for use with a portable appliance (such as a table lamp) also having a 2-way switch, so that the appliance could be independently switched on and off either from the wall socket or the appliance itself. Thus all three pins were used for carrying current, although only two would actually be carrying current at any given time that the appliance was switched on. Possibly it was realised that it could be used as an earthed connector when earthed domestic supplies were subsequently introduced.

WP Maycock's 1911 book "SMALL SWITCHES, etc., and their CIRCUITS" makes it quite clear that the Tripin was intended for earthing applications as well as the use which Emeritus describes.

David

[Nicklyons2]

The first picture, the twin mirror image MK socket, is just gorgeous - I thought I'd seen most of their wares over the years but that model is a new one on me.

I always found it strange that the flush MK 2,5 & 15 Amp sockets had vertical screw mounts but the 13 Amp had them horizontal. The only vertical screw mount 13 Amp I have is an unswitched GEC

[julie_m]

Originally Posted by Nicklyons2

I always found it strange that the flush MK 2,5 & 15 Amp sockets had vertical screw mounts but the 13 Amp had them horizontal. The only vertical screw mount 13 Amp I have is an unswitched GEC

Could that have been intentional, in order to prevent sockets from being installed on the wrong kind of circuit (radial for unfused plugs, ring for fused plugs) ?

[Nicklyons2]

I must say I'd not thought of that - good idea; although it wouldn't stop idiots from putting 15 A skts on 5Amp wiring which would be an even greater danger.

[julie_m]

As long as the wiring actually went back to a 5 amp fuse, it wouldn't be dangerous -- just annoying, because actually trying to draw 15 amps from it would pop the fuse.

A 5 amp socket wired to a 15 amp fuse would be worse; but there were plenty of unfused adaptors about that let you plug a 5 amp plug into a 15 amp socket. Though I'd bet more on some of the flimsy appliance flexes I've seen against a 15 amp fuse, than a 30 amp ring main one.

[Tractorfan]

Hi,
The council estate I was brought up on was built in 1953 and had brown MK unswitched single sockets with the chamfered edges (just four sockets per house). The council gave each household a few plugs as well.
Visiting neighbour's houses, I was surprised at how many (but by no means all) sockets had been installed sideways! I don't know if the back boxes had four fixing lugs or two.
Here's a pic of an MK plug with spring loaded sleeves, as mentioned a couple of posts back.
Cheers, Pete.

[winston_1]

Originally Posted by Nicklyons2

I always found it strange that the flush MK 2,5 & 15 Amp sockets had vertical screw mounts but the 13 Amp had them horizontal. The only vertical screw mount 13 Amp I have is an unswitched GEC

Unswitched MK 13A sockets of the era had vertical screw mounts as did WG.

[G8UWM-MildMartin]

Originally Posted by ajs_derby

A 5 amp socket wired to a 15 amp fuse would be worse; but there were plenty of unfused adaptors about that let you plug a 5 amp plug into a 15 amp socket. Though I'd bet more on some of the flimsy appliance flexes I've seen against a 15 amp fuse, than a 30 amp ring main one.

Three 5-A sockets or one 15-A socket on a 15-A fuse or two 15-A sockets on a 25-A fuse were standard approved circuit arrangements. (11th or 12th edition IEE wiring regs.?)
It was not unknown to run 2-kW fires on them. Although outside their ratings, their (L&N) contacts (especially MK ones) were remarkably similar to European ones still rated at 16A.

[emeritus]

MK did produce 2A flush sockets with horizontal screws: I have an example that I removed from my house when I rewired it when we moved here in 1981. The house It still had its original 1938 wiring, with skirting board-mounted surface switched 2A sockets. The more recent MK socket was from the kitchen, which had originally only had a 15A socket.

On a related topic, I wonder if the screw spacing of the current single boxes that are now used for both switches and sockets, was determined by the dimensions of the wooden boxes that were used for flush switches in pre-war installations? All our original light switches were flush, being recessed in wooden boxes, the switches being screwed to the bases of the box (with cardboard shims to bring them flush), the switch cover plates then being screwed on to the switch body. When I rewired, I replaced all the original recessed wooden switch boxes by new ones at a lower height, except in the toilet (where the switch was immediately above the half-height tiling) and the bathroom (where I fitted a ceiling-mounted pull switch, but "temporarily" left the disconnected original switch in place- it's still there!). I found that the hole pitch of modern single flush switches corresponds exactly with the centre lines of the sides of the old recessed wooden boxes, so I could fit a modern replacement switch in the original box using two wood screws. Indeed, I have a NOS MK brown Bakelite switch that I bought as a clearance item years ago that came with both 4BA machine screws and No 6 wood screws. This suggests to me that the hole pitch of the modern single switches was chosen to allow use with either the old wooden or the current types of recessed boxes.

Re sleeved plugs, I recently came across a 5A example in a hotel that not only had brown/blue pin sleeving, but also specified the frequency of use!

[dseymo1]

On a related subect, does anyone know why M3.5 screws were chosen for more recent fitings?
I could understand it if they were interchangeable with the BA ones, but of course they're not.

does anyone know why M3.5 screws were chosen for more recent fitings?

as near to 5BA as possible so they will fit the holes in older stuff. I have found it odd that electrics use odd BA and electronics even ones, it is said it was a misunderstanding at a conference in the 20's.

[Herald1360]

But old sockets etc are 4BA. The principle works for that though.

I thought it was the Post Office that used odd BA sizes.

[mark_in_manc]

Just browsing - with reference to the clock connectors in posts 32, 59,60: these occasionally turn up in 60s and 70s buildings at the university where I sometimes work, and were used for 24v master-slave clock systems with 1-per-minute pulse operation. I have (from the same source) an ITR pendulum master clock and 2 slaves, but only the male 1/2 of a clock connector so far...pulling the female half off the wall where one still sits seems too likely to incur someone's wrath (and leave an odd-coloured circle on the wall!).

I just measured the slave clock coil resistance (lazily enough in situ, while counting under my breath to avoid frying my ohms range, for a frisson of extra excitement). At about 250 ohms, even a 1A fuse was seriously overrated!

[G6Tanuki]

Originally Posted by winston_1

Unswitched MK 13A sockets of the era had vertical screw mounts as did WG.

And the GEC unswitched single 13A outlets fitted in my parents' house when they had it built in 1958.

[johnpriceuk]

Here's one for ya! Spotted this tonight in a local Conservative Club (doing a photobooth event there)

Appears to be a PA speaker getting its supply from a 5 amp MK round pin high up on the wall? Possibly part of an older unused system, but unsure as the DJ was using his own setup.

Anyone ever encountered post-amp sound being transmitted like this before? I'm a bit of an audio engineering geek but I've never seen this. Of course the 5 amp plug may be feeding something else but I couldn't see anything it could be... maybe an outside light, and the feed goes through the wall behind the speaker, but its far too high to be easily turned on and off...

What are your thoughts? As always I love seeing old MK gear like this out and about, still in use

[julie_m]

It looks more like a 2A socket than a 5A to me. Sometimes these were used for 100V speaker lines -- but I can see another cable in the picture, which could be an audio feed. That would make sense if it was an amplified speaker, getting mains from the round-pin socket, on its own circuit with an isolating switch near the desk.