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Old 31st May 2018, 2:35 am   #1
Boulevardier
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Default 13A Twin sockets.

Split from this thread:-

https://www.vintage-radio.net/forum/...d.php?t=145879


Perhaps a little bit OT, but I think the great electrical scandal of our times is the situation with 13 amp twin sockets. As everyone on this thread presumably knows, they are rated at 13 amps for the whole socket, NOT for each outlet. Thus, it is perfectly possible to draw 26 amps from a 13 amp unit - without any fuse blowing. “Diversity factor” doesn’t save the day - that just says that it’s unlikely to happen...it doesn’t help you if it does happen. When a student, I shared a cold, damp Welsh cottage with an American from Chicago, where they don’t put up with anything lower than shirt-sleeve temperatures indoors during winter. I once came home to find him sitting huddled between two 3kW heaters, both plugged into the same double socket.

MK have tried to calm things down by confirming that ,in fact, all their twin sockets will be safe up to 20 amps. But even then, 20 amps isn’t 26 amps, is it.

This seems to me to be a very basic flaw, and means that the BS wiring system isn’t “consumer safe” or fit-for purpose. I just wonder how it’s been kept so quiet. If my critique is correct, then probably just about every domestic electrical installation in the UK is unsafe, and should be shut down until rewired. How has this been allowed to happen?

But maybe I just don’t know enough, and I’m missing something important?

Mike
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Old 31st May 2018, 3:08 am   #2
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Default Re: 13A Twin sockets.

I agree with Boulevardier. Why on Earth they aren't rated to 26A (with a comfortable leeway, I think they should be able to carry a load of 30A indefinitely personally) boggles the mind. Considering how regulated we are these days, why this hasn't been regulated I cannot fathom.

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Old 31st May 2018, 8:39 am   #3
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Default Re: 13A Twin sockets.

My understanding is that twin 13 amp sockets have be able to carry a total of 20 amps, not 13 amps.
IIRC the test involves 14 amps on one side and 6 amps on the other.

I doubt however that some of the cheap imports actually comply with the relevant standards.
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Old 31st May 2018, 9:43 am   #4
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Default Re: 13A Twin sockets.

Quote:
Originally Posted by Boulevardier View Post
......... When a student, I shared a cold, damp Welsh cottage with an American from Chicago, where they don’t put up with anything lower than shirt-sleeve temperatures indoors during winter. I once came home to find him sitting huddled between two 3kW heaters, both plugged into the same double socket..............
I guess that your American friend might have been comparing the substantial UK 13A plug with thel lightweight US plug and perhaps overestimated its capabilities.

AFAIK diversity on UK 30A ring circuits is largely based on expected heating load and doesn't account for a frozen American student in a cold Welsh cottage .

Martin
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Old 31st May 2018, 9:46 am   #5
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Default Re: 13A Twin sockets.

And everybody refers to them as twin 13 amp sockets!

Alan
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Old 31st May 2018, 10:13 am   #6
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Default Re: 13A Twin sockets.

Since this has always been the case, presumably the number of actual dangerous occurrences arising from overloading a twin socket is well down in the noise compared with other ways to injure oneself using electricity.

For most people, just the cost of running 6kW of anything for any length of time will act as a deterrent!
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Old 31st May 2018, 10:38 am   #7
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Default Re: 13A Twin sockets.

Many imported types won't carry 13 amps for an extended period.
The whole BS1363 system is a compromise between safety and economy; necessary for the post-war era. People expect too much from it; it's mostly safe enough, and more so than many foreign systems still in general use.
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Old 31st May 2018, 10:52 am   #8
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Default Re: 13A Twin sockets.

Quote:
Originally Posted by Herald1360 View Post
Since this has always been the case, presumably the number of actual dangerous occurrences arising from overloading a twin socket is well down in the noise compared with other ways to injure oneself using electricity.

For most people, just the cost of running 6kW of anything for any length of time will act as a deterrent!
Too right! and with the focus on reducing consumption these days is this anything to be bothered about? These sockets have been around 60+ ..years presumably because their safety record is rather good and the consumer unit is there to spread the load to separate circuits.

However the 18th edition wiring regulations have just come out, if this is of concern.
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Old 31st May 2018, 2:26 pm   #9
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Default Re: 13A Twin sockets.

Without central heating in the sixties [even in a modern house] it was common to buy and use stylish 3kw heaters-even all three bars on occasion but not generally. Electricity wasn't particularly cheap then either. Our 1958 semi had a ring main but not many sockets. The front room only had a hard wired wall mounted 3kw heater. No socket at all until I persuaded my parents that I could break into the ring at the fused switch unit for the fire. I keep a grip on my home in the north by severe economies. It's a barn in the winter but I don't run the gas central heating until it's life threatening. Cheapo [warm air] convectors are also cheap to run and I never need to go anywhere near the 2kw setting as they tick over nicely on the thermostat.
On reflection radiated 3kw in the sixties wasn't very efficient. My point is that-

1. It would have been quite hard to overload the ring [then and also now perhaps] for a variety of reasons.

2. Although I knew the rating was 20amps per socket [I'd also assumed 26 at first] overloading seemed very unlikely.

3. As Martin suggested you can't really regulate from exceptions. Plus you can't do it for stupidity. Even in technically dangerous situations a bit of common sense will alleviate things

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Old 31st May 2018, 2:55 pm   #10
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Default Re: 13A Twin sockets.

3 KW fires on a 13 amp plug depended on top quality plug and socket and even then they could get hot. Saw many plugs and sockets with burn marks when fixing TV’s, always advised them to get it fixed before serious problems. Sometimes they got it fixed others just used a different socket. Very often it was the fuse holder that caused the problems, the fork type holders seemed to be the worst type.


I wasn’t trying to sell them the repair, the company I worked for didn’t do wiring.
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Old 31st May 2018, 3:00 pm   #11
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Default Re: 13A Twin sockets.

I found a couple of light switches in our 1960's house that had thin WOODEN back-boxes. This has reminded me that it's high time i checked this has not been done in the 13A sockets- by checking for continuity between the pattress screw-heads.
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Old 31st May 2018, 3:00 pm   #12
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Default Re: 13A Twin sockets.

No full price electricity heating is "cheap to run". Gas is much cheaper, unless you are not comparing like with like (e.g. heating only one room at a time with electric vs. the whole house with gas).

When the 13A+ring main wiring was developed it could be assumed that most people would be fairly sensible, and that not all the load would be in a single place. Fortunately as people have become less sensible in general there has also been a move away from expensive full-price electric heating so these days the kitchen is the most likely place to use a lot of power.
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Old 31st May 2018, 3:17 pm   #13
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Default Re: 13A Twin sockets.

Quote:
Originally Posted by The Philpott View Post
I found a couple of light switches in our 1960's house that had thin WOODEN back-boxes. This has reminded me that it's high time i checked this has not been done in the 13A sockets- by checking for continuity between the pattress screw-heads.
I think you may get continuity anyway through the earth metalwork of the socket, which you may only see if you remove a patress screw.

We have wooden boxes behind the light switches of our thirties house even though the cable and switches have been replaced.

In the sixties MK supplied light switches with alternative 4BA and wood screws to cover both eventualities but I don`t think wooden boxes were ever an option with 13A sockets.
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Old 31st May 2018, 3:21 pm   #14
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Default Re: 13A Twin sockets.

Quote:
Since this has always been the case, presumably the number of actual dangerous occurrences arising from overloading a twin socket is well down in the noise compared with other ways to injure oneself using electricity.
Agreed. I have examined a lot of damaged and overheated electrical fittings and cannot recall seeing a double S/O with evidence of damage by excessive total load. The shared parts carrying the total are after all just two very short pieces of busbar, two rivets / rivetted bosses and two screw terminals. The weakest link here is likely to be the workmanship in terminating the circuit cables, although they are installed by the electrician and left largely undisturbed.

On the other hand, each individual socket outlet with connected plug includes in the current-carrying circuit two each of socket contacts, fuse clips, plug pins, screw terminals, a small heating element (fuse!) and either one or two pairs of switch contacts. Given the likelihood of one or more of these being high resistance or prone to arcing, e.g. a loose fuse clip from clumsy fitting, dirty or misaligned plug pins (which might in turn damage the socket contacts,) a plug terminal screw loose through being knocked around, and any or all of the contacts losing their spring temper through thermal cycling or being of poor quality, there is a relatively high probability of a single outlet dissipating excess heat without exceeding 13A.

By comparison, the likelihood of the circuit connections dissipating excess heat without exceeding 26A is very low, even if their official rating is only 20A. Multiplying this ratio by that of the likelihood of one 3kW appliance being used in a double to that of two, and the risk associated with theoretically limited total rating becomes vanishingly small.
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Old 31st May 2018, 3:45 pm   #15
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Default Re: 13A Twin sockets.

I have a 3kW metal cased fan heater, probably of Chinese origin, which came with a moulded on plug. It was plugged into an MK 13A metal clad twin socket fed from a radial circuit.

The plug melted and one pin, I forget which, welded itself into the socket. I changed the plug for a wired on one taken from my box of plugs and changed the socket for another MK one. All has been OK ever since.
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Old 31st May 2018, 3:53 pm   #16
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Default Re: 13A Twin sockets.

I think there is a great deal of agreement overall on this topic which Mike introduced and it hasn't really had a full "airing" before [unlike a lot of other things]. I'm very happy to take on board your obvious direct experience Frank. There's a lot more to see at both extremes when the job takes you into other peoples homes as I know from [non-electrical] visits. I lived in a small, more frugal and cautious world back then so I suppose that was a safety factor in itself There's nothing completely daft you can think of these days that someone hasn't done and worse!

I think your right about Gasv Leccie overall Dave G8 but I do operate in one room part of the time and the Gas Boiler/radiator run is very inefficient so, in those particular/unusual circumstances, within a big drafty space, it does save me money. I go through a lot of pullovers though!
Dave

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Old 31st May 2018, 3:58 pm   #17
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Default Re: 13A Twin sockets.

In my limited experience the highest likelihood of two high-current appliances sharing a twin 13A outlet could be in the kitchen. Consider a washing machine and a dishwasher plugged in under a worktop. Or a kettle and a multicooker on top. Heating elements tend to draw even more current when cold so the situation might be even worse for a short while after switch-on.

Cheers,

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Old 31st May 2018, 4:12 pm   #18
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Default Re: 13A Twin sockets.

I have exactly that situation. Toaster and kettle plugged into one twin socket along with dishwasher and washing machine plugged into another. Probably fed from the same ring main too.
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Old 31st May 2018, 4:38 pm   #19
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Default Re: 13A Twin sockets.

I agree with Boulevardier, it does not sound at all good!

But, as Herald1360 and Lucian have pointed out, the number of disasters attributable to overloading a twin socket is not high. Luck? Yes partly. But on the basis that consumers' habits are not likely to change, it will continue to be a non-problem into the foreseeable future, while more important things get the attention.
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Old 31st May 2018, 4:40 pm   #20
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Default Re: 13A Twin sockets.

I can't remember the details, but I believe that the regs about ring mains are aware that kitchens are not the same as other rooms.
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