You forget temporal diversity. Moreover, a modern house (which was what was specifically being referred to) would have a separate ring for kitchen and downstairs.
Why has it proven to be so much safer than continental practice then?
How will this improve safety?
In the same way they explained Part P so well that IEE members are no longer considered competent to wire their own homes?
Why not? (Apart from it not being acceptable to the French).
Their evidence being?
Standards have nothing to do with quality.
|Never heard that one.
Available in red as well if you prefer :-)
Eh? I have 24 sockets in the kitchen - you suggest they should all be on one radial and this will be "safer"?
So why don't they? Where are all the fires they cause?
Foot - aim - fire.
And you want to propose ideas from this lot of clowns to the rest of Europe ?
Because all the current systems have problems and to give all existing manufacturers an equal opportunity in what will be a huge market (rewiring half of Western Europe and most of Eastern Europe) they need to have a new design with rights to manufacture. And not even the French would put their system forward as an option - they do recognise some of their own shortcomings. Plus I trust even you recognise the German standard as superior to ours - just it's too expensive.
I think we've seen enough UK people here decrying ring mains let alone the Europeans.
Of course they do - that's the main job of the EN standards after all (or BSI if you prefer them in that format).
And the more technical the product the more you need standards. You should have seen some of the early ADSL modems. Or how about even a current USA mobile phone ?
I hope not.
I also trust you haven't got all 24 sockets on one ring either as I don't believe you can monitor usage that accurately. If you really need this number of sockets then I would have expected them to be wired in physically separated groups on several rings.
However this shows a prime example where the EU proposal would have been better - a 50 or even 100 amp feed to your kitchen's own CU driving short radials to each socket or hardwired item. Instead with the IEE system you've got two or three radials and two rings winding their way to the kitchen - not always a short distance.
Ripping out the wiring of old houses I'm having restored often shows up overheated or burnt insulation. Not every fault necessary leads to a fire - but it could.
They will be safer as the trip will prevent overloads. With a ring circuit it will also prevent overloads provided there are no dormant faults.
It is easy to see which is safer.
It is more difficult to decide how many deaths are worth the cost savings.
Maybe all the unexplained fires?
As John said though, you're not breaking diversity even with that lot:
A 32A ring final circuit is nominally rated at 32A. A 32A MCB or fuse won't trip until well over this amount of current is passing, but the
2*2.5mm2 cables used are capable of carrying quite a lot of load. Your 21A figure is for such cable installed in insulation, but for a correctly installed ring this still gives a continuous 42A rating for the whole circuit. Considering 32A, this is about 7.5kW:Kettle: 2kW for five to ten minutes.
Microwave: Maybe 1.5kW and probably for no more than 5 minutes continuously.
Washing machine: 2kW for ten minutes on a hot wash, and then only for the main wash fill. Couple of hundred (intermittent) Watts otherwise.
Tumble dryer: ok, a biggish one, 2kW for upwards of an hour.
Toaster: probably less than , and only for five to ten minutes
Vacuum: Less than 1kW, and usually for ten minute stretches only.
Bread maker: ours is 700W, but this isn't a continuous load; it is thermostatically controlled and only really uses a lot of power (if you can call 700W a lot) for the final 45 minutes or so when it actually cooks the bread. The rest of the time the heater is just providing a bit of warmth so that the yeast can work.
Grill/sandwich toaster/rice cooker etc: again well under 1kW and short term(ish)
Taking the biggest potential loads there, you'd have to have the kettle, microwave, WM and tumbler all operating at their maximum capacity simultaneously even to reach 7.5kW. This is (IMO) unlikely unless you're in the habit of starting the washing machine while the tumbler is running then immediately deciding simultaneously to make a cup of tea and microwave your TV dinner. Just the time taken to read the instructions and unpack the TV dinner is likely to be enough to allow the kettle to boil!
[...]Depends how you install them. Some houses around here are small enough that you could still legitimately cover them with one 20A radial or at most two. Many are wired with single rings for the entire house. Don't forget that even with a radial you are still allowed as many sockets as you like. Their main advantage is immunity to unbalanced loads and simplicity of adding sockets, but their disadvantage (particularly the
2.5mm2 type) is that it is tempting just to run cable everywhere and so you end up with a circuit that is potentially just as long as a ring would be, but with half the CSA of cable and thus much greater fault loop impedance.That's the best point you've made so far, and it does happen, though usually it is just one of the conductors which has broken. What is more likely is a bad connection causing overheating, and this is likely to have worse effects on a radial where all the circuit current might pass through that connection than on a ring where there is going to be an alternative (hopefully good) path to every other point.
[...]OSG table 6F (4D-something in the regs; can't be bothered to look it up).
20A enclosed in conduit in an insulated wall (method 6), 21A installed in an insulated wall but not completely surrounded by insulation (method 15), 27A clipped direct (method 1) which also, FYI, includes buried under plaster in a wall as this is counted as thermally conductive (method 2).With caveats: for a correctly installed circuit you effectively have
5mm2 of conductor. A spur in 2.5mm2 feeding a double socket is effectively, due to the plug fuses, maximally fused at 26A.Hwyl!
M.
That was part of the thrust of my original question. I have not seen any real explanation of why some think these systems are superior. The germans use dodgy plugs and like radials, but so?
A CU per room seems to offer less discrimination that a fuse per plugtop. Many of the euro systems seem to ofer noi overcurrent protection for appliance flexes for example.
If you want a fuse per light switch then you can have that here (i.e. most dimmer switches).
backed by much in the way of hard fact though?
Try it, you will blow a fuse or open a MCB. You have to work quite hard (or have some other fault condition in place first) to damage a cable.
What was standard practice in the past is not that relevant though is it?
You could argue that if you are going to make major changes there is no need for a new system, but just bringing legacy installations up to current standards.
Have you lived in one?
That was quite common with retro fitted RCD on 15th edition complient setups, but again not current practice.
No disrespect, but it would seem that you don't understand the concepts of diversity (both temporal spacing and loading duration) in this case. What you described does *not* "bust" diversity. In fact your ring will cope with what you describe without drama.
The same fault can affect a radial with a high impedance connection somewhere before its end point. However with a radial you don't have the fall-back of an alternate path to mitigate the effects. (Probably a higher fault loop impedance as well)
When buried in insulation (and if PVC sheathed). Up to 27A when installed in ways commonly used in British homes however. Remember you also have two of them. Increasing use of insulation in new homes may push more circuits to use thermosetting insulations however.
This does not say you can't get situations where you can overload one leg of a circuit, but tat is usually a result of inadequate circuit planning.
That was the bit I did not follow... you have cables to any point good for at least 40A and over current protection nominally at 30A. Note also that short term overloads (which can in fact be hours long) will not result in damages to the circuit (although if encountered frequently may reduce its operational life).
No they dont. It really is that simple. In rare cases where they do overload the 30A supply, there is no safety problem whatsoever. It is simple to see why.
In case you arent aware, fused rings are designed to carry >30A for short periods. It is only newer mcb'ed rings that are limited to 32A proper.
Well Ive seen enough for my report to be that that arrangment is a minority situation used in small flats etc. It is not the norm, and hasnt been for decades.
And fwiw the lighting fuse blowing on a rock bottom grade ancient install doesnt mean no more lights, since plugin lights are so common.
And this says nothing about present practice.
trip?? Youre talking about 15th edn RCDs now? Old installs sure didnt have any trips, other than ELCBs on TT setups which almost never nuisance trip. Need to distinguish between the 2.
NT
Doesnt happen, for 2 reasons.
I've seen 45A of kitchen equipment all running simultaneously on a single ring, it had been in place for about 20 years and no problem. First none of the appliances are 100% duty cycle, 2nd the ring can happpily carry >30A when needed.
yes, and with enough margin that even in a bad case no fire will occur.
NT
I don't think it was ever proposed as the standard domestic outlet. It has become the standard industrial outlet across most of Europe, and does appear (with different current ratings) in the US too. We're quite good at exporting our wiring designs around the world (our 13A plug is used in more countries than any other single plug, but not in much of the rest of Europe; the 2-pin US outlet comes second).
Do not confuse technical competence with the ability to convince a bunch of Euroclown committee functionaries.
I thought the idea was to produce a better system , not to design a feeding trough for German industry? Also do you seriously think any significant _rewiring_ would take place?
Not until I see some convincing reasons, and there have been none so far.
A few ill informed posters does not amount to evidence. Where is the _evidence_ the ring main is unsatisfactory? As I mentioned elsewhere my kitchen has 24 outlets, the small office I am writing this in has about the same. How would this be done in a more satisfactory way using the proposed system than with a ring main?
The main aim of standards is to ensure things are standard, not that they are of good quality. You can have standards that ensure poor quality (and many do - such as SCART), they are still standards and may be adequate for the task.
They are all on one circuit, I don't need to monitor usage and it is perfectly safe. The total load could be about 60A. In order to achieve this I would have to put on the dishwasher, washing machine tumble dryer(timed so all their heaters came on simultaneously), toaster, ice cream maker, food mixers, microwaves, fridge, kettle and coffee maker. If all that lot was on at once the electricity supply would be the least of my worries.
I do, otherwise they would not have been put there.
Why?
So in the kitchen, apparently hidden behind the light switch, I would have 24MCB's? Fed from a 100A cable (The house supply is only rated at 60A)? This makes things "better"?. I think I've missed something somewhere.
It could, the sky could fall in as well, decades of experience seems to suggest it doesn't however.
Well funny enough...
you take the washing out of the washer and put it in the dryer... then you put the next load in....
Then you decide on a cuppa having just done the washing. So you get the iron out and plug it in and then put the kettle on.
And you think it won't happen.....
Yes but with a radial you are likely to notice the problem with a ring the appliances work fine and you don't notice the fault.
I understand them.. I just don't agree with them.
Its just another compromise to save a few quid (very few these days)
So you will find the fault rather than it being hidden by the inadequate redundant path. I have no objections to having a redundant return if the cable is rated to take the full current. Standard 2.5mm T&E are not rated to work as redundant paths.. the return is required for safe operation.
Think about it logically...
You have a rating of about 22A on a 2.5mm T&E cable.. Now you are saying its safe to use up to 30-40A...
If the cable can carry that much current safely then why isn't it rated at
30-40A? Could it be that it isn't safe?
Which bit of SCART gives poor quality?
People just don't blow ring circuit fuses/breakers due to overloading the ring. I've only come across this in poorly designed industrial environments where there's been some change of use of the area and no consideration given to the wiring, but that's going to happen regardless of the wiring topology in this case.
BTW, forget the kettle and iron -- they don't draw power for long enough to figure significantly in the diversity.
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