Fitting a mains plug.

[tomv893]

In my first year at college, we were instructed to train a group of police officer cadets on how to wire a plug.

[Tim]

Talking of shops wiring plugs, my dad bought a new fan heater sometime in the early 90’s and being the most non technical man then alive, asked the shop to fit a plug on it. I checked it later for some reason, and found not only had they used an old second hand plug, they had also wired the blue of the two core flex to the earth pin. Dads house didn’t have an ELCB at that time so the thing worked quite happily, but luckily I found the mistake quite quickly.

I used to be involved with a couple of mobile discos in the late 80’s and I remember having a couple of 3 pin round to BS1363 “Grelco” adaptors, and a 15 amp round to 4 way 13 amp( fused) strip. It was quite common to find round pin sockets still in use in village halls and the like, which of course were common venues.

[TonyDuell]

Rewireable American plugs are not that difficult to find, even the UK. RS sell them, for example. I have 20 or 30 of the Hubbell 234V ones in use on DEC computers in the next room and a box of spares.

Personally I'd like to see moulded plugs banned. They can't be repaired, the wiring can't be inspected and in some cases there's no proper strain relief on the cable. Generally on the rare occasions I buy anything new with a moulded plug, I cut it off, twist the pins so it can't go into a socket, and throw it away. And then wire an MK plug or Duraplug or similar onto the cable.

[stevehertz]

Originally Posted by Tim

I used to be involved with a couple of mobile discos in the late 80’s and I remember having a couple of 3 pin round to BS1363 “Grelco” adaptors, and a 15 amp round to 4 way 13 amp( fused) strip. It was quite common to find round pin sockets still in use in village halls and the like, which of course were common venues.

5A round pin sockets are still current production. Installers and home owners fit them for use with table lamps and so on.

https://www.electrium.co.uk/products...earch=&sortBy=

[TonyDuell]

The MK website indicates they are still making 2A, 5A and 15A round pin UK sockets. Only the 3 pin versions, though. And I think it was a bit of rather bad design that the 2 pin plug will not go into the live/neutral holes of the 3 pin socket (the pin spacing is different).

[Richard_FM]

I've noticed some pubs & restaurants used 5a socket for lighting, often on a dimmable circuit & it stops customers from plugging in phones for a free charge!

I always check the plugs on any second hand items, no horror stories yet but on one TV one of the wires was only staying in the pin by about a single turn of the screw.

[Tim]

The 5 amp and 15 amp round pin plugs might still be used in theatre lighting.

In the mid 80's before you had to sell stuff with a plug on I was in a HiFi shop in Cambridge and a lady came in wanting a lead for her cassette player, the bog standard figure if eight type. The shop assistant fitted an MK plug as a matter of course, free of charge (that must have cost more than the lead) saying "Don't worry madam, we always fit a plug free of charge", service like that? Brilliant!

[G6Tanuki]

The 2A and 5A round-pin sockets [without a switch] were used in hotels etc for powering table-lights/bedside lights etc, controlled by a switch/dimmer by the bed so you could easily turn on/off the room lights while in bed. Some houses also had the same arrangement with 2 or 5A sockets controlled by a switch/dimmer separate from the main room-lights.

[These days hotel room lights often use 'smart' bulbs controlled from your phone using an app]

Regarding 13A plugs and their failures - I've seen several instances where the springy copper fuse-clips are poorly riveted to the brass live-wire screw-terminal or the brass live-pin; on some you can easily rotate the fuse-clip on its rivet. You don't have to be a genius to see what happens when such a plug is used in a high-current application. In the past 'good quality' plugs used solid brass terminals and pins without the troublesome brass-to-copper riveted bit; I guess this fell out of favour because it meant the live lin had to have rather a long slot in it to provide the springiness to grip the fuse, and that would be problematic with the modern requirement for sheathed pins.

[These days hotel room lights often use 'smart' bulbs controlled from your phone using an app]

I assume they will supply a 'phone if you haven't got one?

[broadgage]

Originally Posted by Glowing Bits!

Fuse orientation is critical, the electrons can only flow in one direction but not the other

Only with DC.

[Electronpusher0]

Originally Posted by broadgage

Only with DC.

I always understood that with ac the electrons do not actually flow, they just shuffle back and forth, like ocean waves, the energy wave travels but the water molecules just go round in a circle.

Peter

[emeritus]

The rooms we have had on our stays at Warners have often had the bedside lights connected to unswitched 5A sockets that are not controlled by a wall switch. As these are often the only ones conveniently close to the bed for using phone chargers etc, I used to take with us a short 5A to 13A lead and a WG 1950's 5A "Grelco" double adaptor that was used in the house I grew up in, so we can still use the bedside lamp. I subsequently bought a 3-way 5A adaptor at a pre-covid Harpenden that I now use instead of the two-way one. Using its two side sockets allows the bedside cupboard to be pushed back without fouling the adaptor, which is what happened with the two-way adaptor.

[dglcomp]

Originally Posted by G6Tanuki

Quite a lot of modern stuff takes a significant switch-on surge; it's a characteristic of SMPS design. Using this sort of kit with a low-rated plug-fuse [they're not slow-blow!] can over time cause the fusewire to weaken - its resistance then goes up and it either fails-open or goes into heating-up mode.

In times-past I had to deal with a site where - during the obligatory PAT - the tester replaced the 13A fuses in the plugs with 3A ones without first seeking approval. These plugs were feeding a few hundred really-rather-large Trinitron CRT monitors on dealer-desks; a couple of weeks after the PAT had been completed we started having monitors fail to power-up in the morning, with blown plug-fuses.

The degauss, which fired every time the monitor was turned-on, drew a few cycles of really-rather-heavy current until its posistor warmed-up; this was enough to fatigue the under-rated fuses to failure in a few weeks.

Once the issue was identified I sent one of the team out to scour the local B&Q/Homebase stores and bring back every 13A fuse he could find, these were promptly fitted to every plug overnight. The techies were happy to be paid triple-time [London rates!] to do the work, the problem went away, the client [whose unit-of-downtime was dollars-per-minute] was happy, and he didn't employ that particular PAT-resting company again!

I did replace the 13A fuses in a load of TV's at work as I deemed a 13A fuse overkill for a 22" LED LCD TV even taking into account inrush current.

As for wiring a plug, where possible I use bootlace ferrules, makes the issue of stray strands dissappear and I think it makes for a neater job.

[Tim]

Re post 109. Indeed, I think the spec for plugs was actually changed to cure this problem. The best type have a one-piece live pin with a split/forked end to accommodate one end of the fuse.
I have a few really old plugs that have the fuse receptacle fixed to the live pin by a screw. The problems with that are also obvious, but I do check them now & again and only use them for low demand appliances.

[Lucien Nunes]

Personally I'd like to see moulded plugs banned. They can't be repaired, the wiring can't be inspected and in some cases there's no proper strain relief on the cable.

Obviously different solutions suit different environments so it's interesting to see how oppositely polarised our outlooks are on the subject. I have more or less done the reverse and banned rewireable plugs from detachable cordsets where moulded ones can be used, e.g. 13A - IEC and 13A - bare ends that can be incorporated into equipment.

I work in an industry that uses thousands of detachable cordsets under arduous conditions. I find without exception that sticking to good quality moulded versions improves reliability, despite much lower inspection and maintenance workload and hence lower lifecycle cost. The only situations in which I permit rewireable plugs are those where a strict specification of length is needed; as replacements on captive leads; where moulded sets cannot be obtained of sufficient length, or where on a custom assembly there is more benefit to be gained from having the other end moulded.

Suppose a cordset touring the world has a life of 2 years and is likely to be inspected every 3 months, that's a minimum of 8 times the plug has to be opened just for checks. If we have to make the cordset from scratch and maintain it, the total cost of ownership is about six times the price of a moulded one despite being a less durable solution, as even the best rewireable connectors are typically less impact-resistant than good moulded ones.

Faults (often end-user-induced) are quite often found in rewireable plugs. Under low current usage, internal faults in moulded plugs are vanishingly rare. I could count on the fingers of one hand all the bona-fide intermittent rivets I've seen with an inventory of thousands of IEC cordsets in circulation, compared to hundreds of loose screws. No maintenance possible but no maintenance needed!

[dglcomp]

A decent Volex cordset is vastly superior to probably 90% of hand wired plugs, plus thst cordset has probably been properly tested before being sold, whereas how many hand wired cords have been tested?

[Kala_12]

Seeing the pictures in post #80 reminded me of eight or nine years ago when I was asked to "be the electrician" and lay power to three marquees for a conference.
This consisted of two armoured cables, one to a chain of extensions feeding a pair of strip lights on each marquee pole, the other to supply power for the public address equipment and a band.
This had been done in previous years by a qualified electrician - and before you ask, I was told by the organizers that this had been Risk assessed and was OK. So, first things first, I thought let's look at the cables. All the outer sheaths seemed OK. Next, take the plugs apart to check the connections. Some were nice and tidy, but there were examples of all three of those pictures referred to above, but even worse, of the fifteen or so extensions, three had the screw from the earth pin not just loose but out and rattling around inside. On checking the 2- and 4- way sockets on the other end, yes you guessed, the same sort of thing. When I was asked to do the same job the following year, I checked the plugs and sockets again - two or three leads looked different - more lose screws and one screw found to be missing.
It pays to be thorough!
When I got home, I checked all my extension leads and they were all OK.

Anyway, a slightly belated Happy New Year to you all.
Stuart.

[Glowing Bits!]

Many years ago, I was working as stage crew, there was a giant strobe unit (possibly 1500w) that needed the plug dealing with, the cable was rubber type and needed replacement, I did the best I could to get it to a safe condition before it went on the gantry, the show must go on.

[Vintage Engr]

Originally Posted by paulsherwin

I think this dates back to early terminology when the 'plug' consisted of the thing with pins on it ('plug top') and the thing with holes in it ('plug base'). Even today you still hear sparkies talking about 'plug tops' and 'plug top fuses'.

Agreed, correct terminology - I've never described them as anything else!
My wife begs to differ & gets very annoyed if I use, the word 'Plug-top'.

But then, she actually boils kettles.... (molten metal all over the worktop?)

David.