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Old 31st May 2018, 4:52 pm   #21
Glowing Bits!
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Default Re: 13A Twin sockets.

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Originally Posted by Station X View Post
I have a 3kW metal cased fan heater, probably of Chinese origin, which came with a moulded on plug.
Would it happen to be an industrial square shaped one by any chance?
I have one which eventually created enough heat to blow the fuse, the plug still works but is heat damaged, it shall be changed later in the year before it starts damaging sockets, if it ain't already done that!
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Old 31st May 2018, 4:54 pm   #22
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Default Re: 13A Twin sockets.

Turning into an interesting thread. I can’t agree with some of the comments above - that are really just playing the old “diversity” card. Nothing wrong with designing diversity into an installation - provided it’s the sort of diversity that just means the possibility of a fuse inconveniently blowing now and then. If it’s the sort of possibility that could result in the occasional fire, then for me that’s not diversity, it’s dangerous system design. If that design is sanctioned by the regulations (which it seems to be), then something is badly and irresponsibly wrong with the basic BS system.

Common sense doesn’t come into this sort of thing - whose common sense? My American friend plugging two 3kW heaters into one twin socket shouldn’t be expected to look up their wattage specs and then do a bit of mental arithmetic to work out how many amps will flow to each in a 240V system - he’s justified (as a non technical person) in assuming that a twin 13A socket can be used to feed any two appliances with matching plugs, and that the system has been designed to cope with that.

For me, however you look at it, there’s no way of defending a system that has designed into it the “legitimate” connection of two 13A appliances to an outlet that’s only officially rated at 13 A (which is what is marked on the sockets - even if MK do design for 20A) and where the whole circuit is only protected with a 30 (32) amp fuse.

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Old 31st May 2018, 5:00 pm   #23
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Default Re: 13A Twin sockets.

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Quote:
Originally Posted by Station X View Post
I have a 3kW metal cased fan heater, probably of Chinese origin, which came with a moulded on plug.
Would it happen to be an industrial square shaped one by any chance?
I have one which eventually created enough heat to blow the fuse, the plug still works but is heat damaged, it shall be changed later in the year before it starts damaging sockets, if it ain't already done that!
That's the boy! Probably rated at more that 13A when you include the fan motor. The fan runs permanently.

As stated using electricity to generate heat is very expensive. My boiler is a moderated type with adequate capacity to heat the workshop. It's a matter of installing underground pipes though, but that's off topic.
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Old 31st May 2018, 7:18 pm   #24
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Default Re: 13A Twin sockets.

Further to my post at 9*, I got to improve the whole ring main [at 14] because I was supported by a friend of my dad who worked on Decca Radar during his National Service. He was a bit of a character and ended up as one of the first Energy Consultants to Industry when it was a very new thing! After further thought, I'm sure he told me that the cable was actually rated at 20amps. Coming from both sides of the ring this gave much more than than 26amps at the socket. Of course that's only one in the system but it's what he appeared to believe He was wiring up several of the few remaining Cotton Mills in Lancashire at the time in a "last ditch" modernisation program! The last time I saw him it was on the front of the Sunday Times Business Section headlined "On the way to his first million".

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Old 31st May 2018, 7:26 pm   #25
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Default Re: 13A Twin sockets.

I recently carried out a handful of un-scientific, poorly controlled tests concerning this subject, including drawing more than 13A per outlet. The biggest problem I had was the heat from the 13A fuses. Replacing them with a 1" length of brass rod removed the main source of heat and allowed everything to stay at a sensible temperature.

The products I was messing about with were all of reasonable quality, except for 2 of the plugs that didn't react well to being heated by the fuse, even at 13A. The plastic softening substantially and the fuse clips becoming loose. The increased contact resistance from the loose fuse clips added to the heat causing further damage. With the same load in a quality plug the fuse became very hot but reached a point where the temperature stopped rising. One of the cheap plugs that melted, the fuse became so hot its link melted.

For the serious overloading tests, MK plugs were used and these dealt with the heat from the fuses with no obvious damage.

One of the sockets was a 1970s MK, the type with 4 plate screws, that handled 28A for 30 minutes with MK plugs fitted with 13A fuses, with no visible damage. The metal parts in contact with the fuse became hot, but there was no signs of discolouration, melting or cracking, and the fuse and plug pin clips still firmly gripped. With the fuses bypassed it had no problems at 32A either. Of course repeated overload is likely to be detrimental, but such an experiment at 240V will soon start to get costly...

This issue is certainly not something I would be too worried about. Overloading extension leads and multigang strips is a far more real problem, something I look out for during appliance testing.

I should carry out the test with modern budget brand sockets, after testing the smoke alarms.
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Old 31st May 2018, 7:57 pm   #26
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Default Re: 13A Twin sockets.

Mike [in post 1*] you didn't say what else happened when you went home and found a 6KW load on the double socket? Was anything glowing that shouldn't be? Was it a one off, any damage? Did you end up with a large bill and if so I wonder who paid it? Not a safety issue of course!

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Old 31st May 2018, 8:00 pm   #27
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Default Re: 13A Twin sockets.

I have used an arc welder that draws well in excess of 26 amps when in use, for years with a brass bolt in the rubber plug, never had a problem or damaged a socket.
I think that would test the state of all the ring connections!
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Old 31st May 2018, 8:17 pm   #28
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Default Re: 13A Twin sockets.

That sounds like it relied on the duty cycle for survival!

How long does it take to burn through a whole rod, then change it and continue?

Does that ever actually happen?

Ever thought of fitting the welder (and the workshop) with 32A BS4343 connectors?
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Old 31st May 2018, 8:30 pm   #29
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Default Re: 13A Twin sockets.

Ok..there's always one. My parents' house, built in around 1954, had 13A sockets from new, a mixture of MK and Bill. The sockets were all flush-mounted with woodscrews straight into the skirting boards where a perfectly routed opening had been made.

Mum had most of them raised to about a foot off the ground and into the plaster, because when they went wall-to-wall carpets, anything with a thick mains flex would mark the carpet where it came out of the plug. (originally the house was all parquet floor).
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Old 31st May 2018, 9:09 pm   #30
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Default Re: 13A Twin sockets.

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Originally Posted by Herald1360 View Post
Ever thought of fitting the welder (and the workshop) with 32A BS4343 connectors?
Its used all over the place, indoors and out on the moorings. So there is no way it can always be on a 32 bluey. Not often used for more than 2 or 3 hours continuously but 8mm rod after rod to complete long welds. Still poses no problems other than the 4mm flex mains cable being a nice hand warmer on a cold day.
Does make an old style electric meter jump though.
340 Amps @50v output.

Last edited by Boater Sam; 31st May 2018 at 9:10 pm. Reason: added
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Old 31st May 2018, 9:12 pm   #31
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Default Re: 13A Twin sockets.

"you didn't say what else happened when you went home and found a 6KW load on the double socket? Was anything glowing that shouldn't be? Was it a one off, any damage? Did you end up with a large bill and if so I wonder who paid it"

It was a one-off event as far as I was concerned - and 40+ years ago, so not fresh in my mind. I think I arrived shortly after switch-on, and pointed out the problem. I think he was warm enough by then, so was happy to turn off one of the heaters. I needed to get back to my philosophy books, so, having removed the risk, didn't get around to checking for damage.

I've also always had issues with unfused spurs feeding twin sockets through 2.5mm cable - again, up to 26A through 20A rated cable (that is, 20A if buried in plaster) and nothing in the way except a 30A final ring fuse. I've often wondered if this all came about when, possibly some time late 1950s or 1960s, the norm switched from single to twin 13A sockets, and a "single" socket changed from meaning 1x13A to 2x13A outlets - and no one thought to update the Regs.. .!
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Old 31st May 2018, 9:37 pm   #32
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Default Re: 13A Twin sockets.

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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.
Let's not forget that in most houses, the kitchen is usually a separate ring main, from other parts of the house. Then it's a ring main, where two 2.5mm T&E leave the fusebox, and go to differing ends of the ring, so the effective current capacity of the ring ( on cable capacity) is 50A, although most of the ring mains have MCB's rated at 32A. I'm in the middle of a kitchen refit by my LA (council) and they've decided that 4 x13A double sockets (plus a fused spur or two for cooker hood & ignition of gas hob) are OK. Seperate 40A supply has been fitted for (in our case) electric oven or for a following tenant with a free standing cooker. But I can see the point, that is being made. We've got kettle + toaster (both circa 2kW), albeit short term draw, then 900W (assuming 100% efficiency) microwave, again short to medium term use and 17OOW Air fryer and all on same ring, and the washer spurred of off same ring. That's about 7000W (31A @ 220V) on two cables where the MCB is 32A, without the load of the washer heating water. And that's just with half of the total socket allocation. Working out the loading on each cable would be like the theorem (I can't remember the name of at moment) on current distribution in parallel resistor networks.

Most ovens are circa 2.5KW , so could conceivably be used on the kitchen ring, as a lot are fitted with a 13A plug. And that was topic of a lot of discussion with electrician doing the rewire and resulted in the "cooker" feed being routed to allow for the oven to run off it and relieve the ring main of some load. But you can imagine the discussion in ye electrical shoppe, with a salesman looking at the oven rating of 2.5K and saying "that will work ok on a 13A socket". They will, but I've had this sort blow 13A plug fuses, and (I am not a sparky) prefer if possible to use the 16A outlet on my board designated Water heater, and redundant as we have a comb.

Someone mentioned 18th edition regs- sparky did mention this as a possible "about to arrive" - any information on date of release ?
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Old 31st May 2018, 9:49 pm   #33
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Default Re: 13A Twin sockets.

What you say about fixed wiring is true, but the question arising in this thread is whether a twin 13A socket can handle 26A. Apparently not!

I don't recollect whether my kitchen has its own ring main, but I suspect not. The original 1930's wiring was replaced with PVC stranded tinned cable at least 50 years ago when standards were different. I did find that the main earth was a piece of thin red wire connected to a hot water pipe! Not any more though.
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Old 31st May 2018, 9:53 pm   #34
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Default Re: 13A Twin sockets.

" the question arising in this thread is whether a twin 13A socket can handle 26A. Apparently not!"

I would say definitely not. Even a quality manufacturer like MK only claims 20A handling.
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Old 31st May 2018, 10:12 pm   #35
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Default Re: 13A Twin sockets.

I think you've certainly made a "Prima Facia" or whatever case Mike. I'd definitely have you round to do a re-wire no question

Thanks for answering my impertinent questions. I thought maybe the social consequences might have been worse than the technical ones I once stayed in a similar Welsh cottage but the way the slot meter was set up meant that the only possible overload would have been on my bank account

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Old 31st May 2018, 11:00 pm   #36
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Default Re: 13A Twin sockets.

Quote:
Originally Posted by Station X View Post
Quote:
Originally Posted by Glowing Bits! View Post
Quote:
Originally Posted by Station X View Post
I have a 3kW metal cased fan heater, probably of Chinese origin, which came with a moulded on plug.
Would it happen to be an industrial square shaped one by any chance?
I have one which eventually created enough heat to blow the fuse, the plug still works but is heat damaged, it shall be changed later in the year before it starts damaging sockets, if it ain't already done that!
That's the boy! Probably rated at more that 13A when you include the fan motor. The fan runs permanently.
It sounds like yours relies on air movement past the stat probe to detect air temp.
The fan itself will consume in the region of 50w.
Regards, Rick.
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Old 1st Jun 2018, 12:23 am   #37
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Default Re: 13A Twin sockets.

Separate ring for the kitchen? Luxury!

My 3 bed house has but four circuits; upstairs lights, downstairs lights, cooker and sockets. The 'sockets' circuit has about twelve double and three single sockets, plus the fire in the lounge and the immersion heater.

The house was built in 2001 so presumably my wiring complies with regulations then in force.
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Old 1st Jun 2018, 12:29 am   #38
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Default Re: 13A Twin sockets.

I must admit, I had always assumed that a 13A double socket faceplate could withstand 13A to each outlet-- not just 13A for the whole faceplate. In practice, the only really heavy loads are going to be in the kitchen, and only used for a short duration. Even a washing machine is not going to be drawing its full rated current continuously; only while the water is heating, and a well-designed timer can even ensure that the heater turns off before the motor comes on, and vice versa, so there is diversity within the appliance.

Fortunately, in my kitchen, all the heaviest loads -- washing machine, kettle and microwave oven; I do not have an electric toaster, as I prefer the taste of gas toast -- are all plugged into separate faceplates. Although the washer and μW are on a double spur, which would not be allowed by modern regulations but was deemed OK when wired. Still, they only consume 2.5 and 1.3kW respectively, so just about within the permitted 20A for one double faceplate, and rarely used together anyway. The other two sockets are only ever used for short durations and with light loads such as a blender or electric carving knife, or an 800W breadmaker when the washing machine is not in use. (The breadmaker's heating element sometimes comes on intermittently to warm the dough ingredients on a cold day, but is only ever energised permanently after the kneading has finished and the dough been given time to rise. Internal diversity again!)

The only other high-current load is a two-burner electric hotplate which I use for cooking on sunny days, when I can generate enough with my solar panels to cover its demand. But then I am making a conscious effort to stay within the limit of my own generating capacity anyway.
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Old 1st Jun 2018, 9:31 am   #39
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Default Re: 13A Twin sockets.

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Separate ring for the kitchen? Luxury!

My 3 bed house has but four circuits; upstairs lights, downstairs lights, cooker and sockets. The 'sockets' circuit has about twelve double and three single sockets, plus the fire in the lounge and the immersion heater.

The house was built in 2001 so presumably my wiring complies with regulations then in force.
My 3 bedroom house was built in 1978 and has 6 circuits:
Upstairs lights, Downstairs lights, Ringmain, Cooker socket, Shower, Airing cupboard.
The Airing cupboard circuit feeds the immersion heater and central heating controls including pump.
The ringmain feeds upstairs and downstairs including the kitchen with a total of 4 double sockets and 13 single sockets.
Not bad for a 1978 build and because we have central heating two major loads are avoided. I do use extension leads off some of the single sockets in the living room but all light duty stuff such as the tv, wifi, laptops and phone chargers.
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Old 1st Jun 2018, 9:36 am   #40
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Default Re: 13A Twin sockets.

As many folk have said, continuous use of one 13A load is unlikely because of cost reasons, let alone two from the same double outlet, what about electric car charging?

A full electric car will need at least a “cooker point” type of connection to get a reasonable charge time, but a plug-in hybrid might recharge overnight on 13A, and an eco minded family might just have two such cars in the same garage....

Just to put some numbers on this, and without wishing to make this a car discussion, I believe the biggest battery in a Tesla is 90kW/H, or 30 hours at 3kW, but an overnight charge could well be enough for the much smaller battery in a hybrid car. Still many hours on that 13A socket, and cost effective against the cast of petrol.

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