How are single socket spurs adequately protected on a 32A ring?

[Adam Wadsworth]

You are quite capable of distorting what you have said without my help.

-- Adam

[Adam Wadsworth]

So you don't want that electric chair we have all made you for Chrismas?

-- Adam

[dennis]

Its a risk, it arises because the protection isn't there in the correct place. All risks are theoretical, some happen more often.

[dennis]

Its a risk, it arises because the protection isn't there in the correct place. All risks are theoretical, some happen more often.

[dennis]

I haven't changed what I said in this thread even if you have. You even brought 32A spurs into it and ignored that I said "they introduced radials with breakers that actually protected the cables" knowing full well that 32A radials don't do that but 20A ones do and that 20A radials were a later addition.

[Adam Wadsworth]

Lies again Dennis. You said "A radial circuit will not do that, the breaker will trip before the cable can melt as no cable is rated below the breakers rating."

No mention of 20A MCBs, just a mention of radials circuits. It was not until I pointed out to you that 4mm 32A radials can have 2.5mm unfused spurs that you decided to change your wording to include 20A radials.

-- Adam

[dennis]

Well you are the electrician not me, I forgot about 32A radials and would never use one anyway, they have the same design faults a ring has and more on top, not really surprising I never even thought about such cr@p.

And what I said is actually true in your context as well as in my understanding so it can't be lies.

In case you can't understand simple logic.. a radial circuit includes 32A (which I had disregarded as being no use so long ago I didn't even remember them) and 20A radials so what I said was true then and is true now. If I had said all radials had breakers that protected them then that would have been untrue (even though I may have thought it was due to me having forgotten about the cr@p 32A radials). So when you claim it was a lie it shows you don't actually understand English.

Its all done and dusted anyway, the figures in switchedON and those posted by others prove what I said.. you can overload the 2.5mm cable in a double spur without modifying the circuits in any way. The fuses in the spurs do not protect the spur's cable from overload and neither does the 32A breaker. There is no argument you have used that refutes this.

At best you can claim it never happens because people don't plug two extensions into a spur and use them for high current devices. This may or may not be true, neither you nor I can know. Murphy says they will and I have every faith that he is correct, Murphy is always correct in such matters.

The obvious solution is to only allow 8A fuses in extensions, but that would require the removal of all the existing extensions.

It also allows a ring to be seriously unbalanced if you do the same thing in a double near one end but that is another debate I don't want to bother about.

Unless you have some new facts I consider this to be closed.

[Adam Wadsworth]

age

An admission that you were wrong.

Back to twisting the history of your words in the next paragraph.

I have no problem with understanding English. It is the Denglish you speak that causes problems.

The obvious thing is to follow the regs and not make stuff up.

Something else you would not understand.

You ignore facts and live in Denworld

- Hide quoted text -

-- Adam

[John Rumm]

Which part of one single or one double do you not understand?

A flex outlet on the end of a spur would typically feed a single fixed appliance.

If you want to hardwire an extension lead into a flex outlet (not something I would recommended), then you are back to the normal limits of no more than two sockets.

[snip]

The breaker is required to *always* provide fault protection at the origin of the circuit.

The circuit also needs overload protection, and this can, and often is, also provided by the circuit breaker at the origin. However there is no requirement that this is always the case. Some circumstances allow for the overload protection to be provided elsewhere and by other means.

A spur from ring circuit is an example of this. The overload potential is limited by the number of outlets supplied.

A 3A flex on a pendent downlead on a 6 or 10A lighting circuit is another. The overload protection is limited by the devices you can connect.

A 32A MCB feeding two cable runs in 2.5mm^2 T&E - one supplying an immersion heater, and the other supplying (for example) a wall mounted radiant heater in a bathroom) is another. The overload limitation is set by the appliances connected.

For most practical purposes it does. You also need to understand what happens when you draw 40A through a bit of 2.5mm^2 T&E. The answer is nothing initially - it does not immediately go bang or catch fire. You need a sustained overload to cause damage, and that is very much harder to achieve.

Even dumb people seem to be able to understand that loading multiple high load devices onto an adaptor or multiway extension lead is a bad idea. Why can't you?

Now for the avoidance of doubt, Am I saying that multi way extension leads are all fine and dandy? No I am not. There are certainly quality issues that may need addressing if nothing else. The fuse in the leads plug is designed to protect the flex to the leads sockets and there are cases where it is questionable if it is doing this well enough.

Do I think this is something that requires modification to the fixed wiring practices to correct? No I don't - the fault rests with the appliance, so fix that.

A trailing lead is after all an appliance, if it has the possibility of introducing a load in excess of that the plug and socket were designed for, then it is something to address in the design of the lead. Down rating an entire circuit in an attempt to mitigate the problem makes about as much sense as limiting a car's top speed to 30mph, because there are poor quality counterfeit break disks available.

You may recall it was either Adam or I who first posted the link in question.

What did it show?

That the leads in question fail fairly spectacularly with a 20A load. As others have highlighted, many will struggle with 10A.

For a few minutes...

You have seen what happens to the trailing lead when you try it.

Just as well someone smart engineered our fixed wiring practices to cope with short term overloads isn't it.

What does a 20A circuit rely on to protect from overload?

A 20A MCB won't limit the current to below the cable's rating and make your perceived problem vanish, since it will quite happily supply 40A for an hour.

There are occasions where a BS1362 fuse will be used for overload protection, but you won't find them in plugs when doing so.

Examples include when used in fixed wiring to feed a fused spur feeding multiple sockets. In these cases they are (as usual) protecting the downstream cable since there is no limitation on the number of outlets with a fused spur.

[David Robinson]

:

I'm so glad that one of the tests I'm doing on my new installation is shorting the cable furthest from the CU on each circuit to see what happens!

Cheers, David.

[dennis]

Which part of what you said don't you understand?

Are you confusing flex outlets with fused connection units? You know the ones with a fuse in them that you said are not required.

You shouldn't wire anything into a flex outlet on a ring main or a 32A radial as they lack fuses.

You are ignoring the facts. I and others have provided figures that show this is not the case. You can wire in a double socket and take 20A from each without blowing any fuses or breakers. Show me the calcs that show this doesn't overload any part of the cables.

At least in that case you are probably right. There were plugs available for you take power from light fittings but they aren't sold in many places these days. My parents had them and I dare say there may well be some still in use.

Are you sure that's in the OSG?

Its easy to do, it doesn't require any tampering with circuits, any tools and worst of all any knowledge of how to. In fact it the last item that is the problem, anyone can do it and not even know. The protection mechanisms are there to prevent this happening, if they worked that is.

You underestimate how dumb most people are. They probably don't know its a spur in the first place. They don't know how to convert kW into amps. They probably know that they shouldn't daisy chain extensions which is a shame as that wouldn't cause the problem in the first place.

The fact we are having this debate proves I do. It does make me wonder if the same is true of you though.

So you think that its fine for an appliance to be able to compromise the fixed wiring? an appliance that the electrician that did the fixed wiring has no control over. It always makes sense to put the protection of the fixed wiring in the fixed wiring and not in some device not under the control of the installer/designer. It is expected that the designer/installer should allow for misuse intentional or unintentional. What exactly is the point of any safety device if its used correctly? To cover mistakes in the operating manual?

The plug is an integral part of the design of ring mains. To fix it is a change to the design.

I have not suggested down rating the circuit so why confuse the issue? Its easy enough not to run spurs in 2.5 mm cable on 32A breakers.

So what? It doesn't require any faulty or fake bits to cause the overload.

You had better quote the post then because I didn't see any such thing from you or adam.

It showed that the fuse didn't limit the current to a level where the fixed wiring was not overloaded.

You had better ensure they outlaw 2.5 mm flex then, we don't want anyone being able to make an extension using it do we?

Absolutely nothing, you can easily get 20A down 2.5 mm flex without it even getting warm and it won't blow the plug fuse. You could run a high powered arc welder for days from it and the fuse wouldn't blow.

Are you claiming the cable won't take that current for an hour? If it can then you argument is invalid.

OK I will accept you statement and use it as proof that there the IEE didn't design in any spur overload protection at all. they just stuck their finger in the air and said well if they only plug in two appliances all will be fine, nobody will ever find a way to plug in more. I'm sure they will agree with your statement and what it means.

[John Rumm]

Well it makes sense to me and most others.

No, I meant a flex outlet - i.e. switched or unswitched, but no fuse.

Why would you need a fuse if you were connecting directly to a fixed appliance with no downstream cable to fault protect?

Depends on the circumstances. I gave you an example last time where further fusing would not be required.

For the few mins until the contacts in the socket fail or the plug gives up the ghost, or more likely, until the 1.5mm^2 flex fails where it is connected to the trailing leads socket or plug.

The likelihood of one seriously overloaded trailing lead being connected to a socket is relatively slim, although no doubt it happens from time to time. Chance of damage to fixed wiring is nil. The chances of two being connected to the same double socket would seem vanishingly small. Even then you have little to worry about (other than the overloaded trailing lead melting). As a fixed wiring issue this really is non problem. It may well spell doom for the poor socket, and will almost certainly kill the extension leads.

It may well overload the cable for a short time, however the design allows for that. Fault protection would not be compromised at all.

Ah, bless.

Banned decades ago...

Indeed there may, however for the kinds of things they were typically used for its probably a non issue. (a bigger problem is accidentally pulling the downlead out of the rose)

Say both fixed loads are 13A, Each is fine on a 2.5mm^2 T&E, so overload of the cable is not a possibility. The combined load is within In for the breaker, so that's fine. The only remaining question is fault protection, and since we already know that a spur has more than adequate fault protection from a B32 MCB then that is also fine so long as the maximum cable lengths are not exceeded.

So you maintain, but can you honestly see anyone finding enough appliances to consolidate onto a single socket to provide a sustained

40A load?

Perhaps you should enlighten...

True, not that it matters much.

Probably true, although most people have a reasonable idea the large heaters etc are high load devices.

Generally I find most people who claim little knowledge of electrical matters actually have the message about not overloading sockets reasonably well. In fact they usually ask the opposing question, such as "are all six of those things plugged into that extension lead ok?" when looking behind the computer or hifi etc, and one needs to explain that in this circumstance its fine since they are all very small loads.

And yet that is a practice that is more likely to hurt them in reality, as the ELI climes to unacceptable levels.

Your question presumes that an appliance can compromise the fixed wiring... Should one design an appliance that draws 5kW and fit it with a 13A plug, no obviously not. Will one 20A load on a socket compromise the fixed wiring, not a chance. Will two of them ever be combined at a single socket location in a domestic setting - two chances, slim and fat.

Which is how its done. You are the only one maintaining that plug fuses are designed to protect upstream wiring.

No, the fused plug is an integral part of facilitating 7.2kW circuits. It has nothing to do with their topology. Without the fuse then the circuit breaker would have to provide fault protection for the appliance flexes as well as for the fixed wiring, as is the case in the US and some parts of Europe. That in turn severely constrains the maximum power that can be delivered by the circuit

With new installations, then one generally does not use many spurs, although strategic use of them can save eating into your cable length budget in some cases.

Spurs are however allowed, standard practice, and widely used and they rarely seem to cause a problem (the one notable exception was with old T&E using a 1.00mm^2 CPC, on circuits with a 30A BS3036 rewireable fuse at the head end. There it was observed there was a genuine cause for concern since adequate fault protection could not be guaranteed. This did result in a change to the circuit specs to raise the CPC CSA to

1.5mm^2).

> What did it show?

No that is a figment of your imagination. The entire article did not mention fixed wiring even once.

They did say:

"As expected, it was the results of the overload and temperature rise test that gave the most concern. In all but one case, the supply lead plug on each sample showed varying states of overheating damage and enclosure deformation. The accessible surface of the fitted plug was measured for five of the seven samples. The lowest recorded temperature was 84.5°C and the highest was 200°C.This highest temperature softened the plug body leaving the line conductor pin in the mains socket-outlet after the test, as depicted in Figure 1. Significant damage was also observed for one other sample where the accessible surface of the plug reached 153.4°C, as depicted in Figure 2."

No mention of fixed wiring related issues you will note. In conclusion, were there recommendations to alter the 17th edition of BS7671? No there was however:

"Nevertheless, the findings of the research reinforces the need to provide consumer advice about the dangers of overloading extension leads with further suggestions for keeping the area around the extension set free from dust and other combustible materials. We will also encourage users of extension leads to carry out regular visual checks to look for signs of overheating damage at the plug and socket-outlets and to do routine maintenance operations on the supply plug, flexible lead and four-gang socket-outlets."

All the COTS leads use 1.5mm anyway. Using 2.5mm Won't slow down the failure of the plug that much however. (the weak point in most plugs are the skimpy terminals on the wire end of the fuse, and limited contact area on the pin end).

And?

No, not at all. Quite the reverse. I was highlighting that its the combination of the magnitude *and* the duration that is significant.

Did you miss the bit about a limited number of outlets? Do you understand the role of diversity?

Amazing how well it has worked really isn't it.

[dennis]

8< snip desperate ramblings of someone quoting lots of dangerous things that AFAIK are not in the OSG and have no calcs with them to show they comply with the regs.

link does not show a link to what I posted. It doesn't link to an iee publication to start with or to a posting with said link.

No it showed exactly what I said, the fuse doesn't limit the current enough, the breaker doesn't limit it enough and now you think the meltdown of the appliance is going to protect the fixed wiring.

8< as above.

This is pointless, you carry on as you like, I will continue to exceed the requirements of the regs where I do stuff. I will not put in a circuit where the current can continuously exceed the cables rating whether it is in the regs or not! Its you that is cost cutting and I hope it doesn't bite.

BTW ARW thinks the current is limited by the plug fuses just in case you still think nobody else does.

[dennis]

8< snip desperate ramblings of someone quoting lots of dangerous things that AFAIK are not in the OSG and have no calcs with them to show they comply with the regs.

link does not show a link to what I posted. It doesn't link to an iee publication to start with or to a posting with said link.

No it showed exactly what I said, the fuse doesn't limit the current enough, the breaker doesn't limit it enough and now you think the meltdown of the appliance is going to protect the fixed wiring.

8< as above.

This is pointless, you carry on as you like, I will continue to exceed the requirements of the regs where I do stuff. I will not put in a circuit where the current can continuously exceed the cables rating whether it is in the regs or not! Its you that is cost cutting and I hope it doesn't bite.

BTW ARW thinks the current is limited by the plug fuses just in case you still think nobody else does.

[John Rumm]

Yourself I take it...?

>>> That link does not show a link to what I posted.

Let me quote what I said for you:

"There is evidence that some of the lower quality (i.e. probably cheaper) 4 way leads are not adequately protected by their 13A fuse - since this will usually permit a sustained load of 20A and not all of them are up to that. Read the report starting page 18:

"> It doesn't link to an iee publication to start with or to a posting with > said link.

I think you will find that links exactly to the issue of Switched On that you were referring to (which is not an IEE publication, but a ESC one). The intro I gave it should also give you a fairly good clue. Note that before you claim day is night, your actual words are there in this post for all to see.

More lies dennis...

Indeed. I am sure there are better things you could be doing with your valuable time. Why not send some of your ideas to the IET? I am sure they could do with a laugh as well.

I am sure he does and I agree with him - fuses limit current flow in downstream circuits. You will note I said above "There is evidence that some of the lower quality (i.e. probably cheaper) 4 way leads are not adequately protected by their 13A fuse".

Upstream circuits are either overload protected by their fuses/MCBs or there are circumstantial factors in place that prevent overload in the first place.

[Huge]

John, could you consider giving it a rest and just killfiling dennis and getting on with your life, like most of the rest of us have?

[Andy Burns]

If it bothers you seeing people reply to dennis, why don't you kill each subthread that dennis replies to? Then it won't matter to you if anyone else engages him ...

[Huge]

I suppose I could killfile on the References line. Anyone else of any significance post from news.datemas.de?

[John Rumm]

(you could have killed the thread...)

Tis ok, I have stopped now. ;-)

He seems to be stuck looping now... having argued himself round and round in circles long enough, we are now back to the idea that the reason we are all wrong is because only he alone knows the one true answer. I am sure the IET are looking forward to handing the whole production of the 18th edition over to him.

[dennis]

>>>>>> That link does not show a link to what I posted.

either. Are you confused? You sure appear to be.

That link might but not the one you posted. Sorry I said it was iee it looked like it was from the bit I looked at.

Now you are telling pokies again.

That isn't what he said.

I don't really care about your fixation with faulty fourways, I do find it odd that you need a bit of faulty kit to provide protection against faults. If it isn't faulty or poor quality it wont melt and your safety device doesn't work. Lets hope nobody makes safe fourways then as we don't want any that might not melt to protect the spur.

Circumstances that rely on a user doing the right thing even though they don't know they have to do it or what they have to do. Sounds pretty good to me, well done. All it needs now is a manual written in Cinglish so we can be sure they do the wro^Wright thing.