Although lighting circuits are normally protected at 6A, the 1mm² wiring is actually rated at 12A. The lower value protection is required because of the choice of lampholders on the circuits.
Fires tend to start at wiring accessories, cable joins, etc, and not so much in the middle of a length of wire.
Normal UK home has a 100A (24kW) supply. If you want any more than this, you have to have a 3-phase supply, but that's quite unusual in a home unless it was very big.
Your analysis is too simplistic. The load current / cable rating is not something that causes any significant number of fires in either case, it is a nonissue in reality.
Also I assume you realise 1mm2 is capable of much more than 6A, it is merely fused at 5A or MCBed at 6A.
Safety margin is determined by looking at what in the system causes safety failures, and how often. Cable rating doesnt come into it. Your heavy US cables are merely a waste of resources, achieving nothing afaics.
Unless you can explain how 4A on 32A capable cable tripped at 15A is safer than 4A on 15A cable tripped at 6A. (figures are examples, not calculated)
to be honest I dont know what youre referring to, youve snipped the relevant stuff out.
But I remember just enough to be fairly sure the assumption above didnt come into it, that IIRC you misunderstood what was being said.
Youre not understanding safety margin. Size of cable has nothing to do with it, once the cables big enough not to overload. Ours are big enough and much more. Yours are even bigger, but for what? Its just poor engineering.
Above ground supply or buried? 85mm2 is awful big, even for 200A. Or is it aluminium?
Again you miss it. Your systems are overloaded day in day out, not at the service entrance but at the wall plugs that get too hot, and the wirenuts that cant reliably maintain their ratings. The result is a high level of fires.
precisely, here theyre illegal and unheard of. There isnt even a black market in such junk, its just off the scale. Even the occasional 50 year old install isnt that bad.
yup. the question is which is the greater number. 240 gives much better clearance rate than 120.
if you could quote all relevant material I might be able to answer.
NT
Because voltage drop is a serious issue for 120V supplies. It's not for 240V supplies.
snipped-for-privacy@meeow.co.uk wrote: Various wrote
Many new lighting fittings on sale in the UK today use push in connections! Probably other connectors as well.
Regards Capitol
On 4 Jul 2005 11:11:49 -0700,it is alleged that snipped-for-privacy@meeow.co.uk spake thusly in uk.d-i-y:
[snip]
Dunno, they seem much sturdier against mechanical damage (stripping etc).
Generally Alumin(i)um wiring for the service entrance cables upto the main breaker in the distribution panel.
[snip]Wall outlets and plugs don't get hot when they're new, it tends to be the older ones that are loose that overheat. I never in 5 years in the US saw wirenuts that couldn't maintain the ratings *when installed correctly*.
Most fires are due to overloading extension cords, that is one thing that really SHOULD be changed, they allow 13 amp rated (16AWG) ext cords on 20 amp circuits, which is a recipe for disaster, one that all too often works well:-(
As someone else has noted, they are appearing on lighting equipment and scare the bejesus out of me, the ones that are on light fixtures make the US backstab connections look secure.
[much snippage]Not trying to further the war:-) Just observations I made.
is that one of the big causes of fires though?
ok, so they are a problem.
If users routinely cant install them safely, even after over half a century of use, theyre a safety problem. Whatever the mechanics of it, they do cause fires, but are still used. Strips of 12 screw connectors are very cheap here, even if not as cheap as wirenuts. The cost to save those lives is trivial. Add in the great cost saved in damaged goods, and the US's use of wirenuts seems to make no real sense.
why would that cause disaster, given the large cable safety margins?
and why permit 13A rated cable on 20A circuits?
If what youre saying is accurate, the next question is why.
We use them only for low current apps in UK, for which they work satisfactorily. Trying to put over 10A through them is another matter. They will only maintain a gas tight connection over a very small contact area.
NT
is that one of the big causes of fires though?
ok, so they are a problem.
If users routinely cant install them safely, even after over half a century of use, theyre a safety problem. Whatever the mechanics of it, they do cause fires, but are still used. Strips of 12 screw connectors are very cheap here, even if not as cheap as wirenuts. The cost to save those lives is trivial. Add in the great cost saved in damaged goods, and the US's use of wirenuts seems to make no real sense.
why would that cause disaster, given the large cable safety margins?
and why permit 13A rated cable on 20A circuits?
If what youre saying is accurate, the next question is why.
We use them only for low current apps in UK, for which they work satisfactorily. Trying to put over 10A through them is another matter. They will only maintain a gas tight connection over a very small contact area.
NT
On 5 Jul 2005 04:12:31 -0700,it is alleged that snipped-for-privacy@meeow.co.uk spake thusly in uk.d-i-y:
[snip]
Through arcing faults if the cable breaks, it can be.
Yes but I've seen the same with the fuse clips on 13 amp UK plugs. Some makes seem to work loose, this is now mostly fixed. US socket outlets had the same issues, which are now also mostly fixed.
To be fair, I have seen strip connectors cause burn ups too, personally I prefer wirenuts as being easier to install.
Many fires with wirenuts were caused by their use on Al cable, in a few cases with UL approval. This caused and still causes a lot of anger with US electricians who know from experience it doesn't work, but nobody listens to them. Pretty much the same as here:-(
Those safety margins are for fixed wiring cables, the fire usually starts right where someone put the extension cord under a rug.
Indeed.
Germany and Austria use the 'Wago' brand push in connectors, these seem to have VERY high contact pressure compared to the ones on ballasts and lampholders, personally I'd trust them at ~16 amps.
I think we should agree to differ over which wiring system is 'best' overall, my opinion would be 'neither, they were both designed by committee, but each has strengths and weaknesses, surprisingly often in the same areas'.
A *lot* of military hardware, neither afloat nor airborne, uses 400Hz for power distribution, not just to cut down on the mass of transformers, but also on their bulk.
A radar system with which I spent many years (it was first designed, but never built, to go with a Predictor and the Vickers 3.7in AA gun, ca.1946, but not constructed until the early/mid 1950s, and to my certain knowledge was still being used, in a different role, right through into the 1990s) had more than five HUNDRED power transformers operating off "400Hz mains". Each sub-system had its own transformers for valve heaters, HT supplies to anodes, EHT to klystrons and magnetrons, etc.
(The 400Hz "mains" came from a motor-alternator set, running off 3ph 50Hz [which came in our instance off the public supply, but "in the field" could arise from a pair of 27.5kVA Meadows diesel alternators]. The startup current at switch-on was sufficient to bend the needle on the electricity board's engineer's tong ammeter, even though it was on the
400A range: he was there to investigate our complaints of insufficient iron in the substation transformer ;-)
Well, perhaps I should have broadened it to say portable/transportable.
I also got some private feedback from someone who used to be in the supply industry who said transformer size _is_ important to them -- they want them big and heavy, so they can't be stolen ;-)
Actually it is the energy current times voltage.
For a given fault twice the voltage equals twice the current!
safer does not equal never.
British cars from the 60's were notorious for electrical fires.
I never claimed lower voltage was inherently safer, I said with similar safety margins, it is similar in fire safety. When deployed with greater safety margins it is safer.
Remove SPAMX from email address
No again. Faults are not normally ohmic. Higher v creates much higher i, and of course higher v means lower i breakers... result is a big difference in fire rates, favouring 240. 240 clears faults much better.
NT
Chip wrote: snipped-for-privacy@meeow.co.uk:
all components have a failure rate, the question is the comparative rates.
I dont think we allow that here! I cant offhand think of any domestic wiring sceanrio thats permitted in UK by the 16th but dangerous... maybe you can. The death rate is remarkably low.
so why are cables with inadequate margins used? Our regs in UK are the other way, very conservative.
ok. I'll just compare the death rates.
NT
On 6 Jul 2005 13:15:48 -0700,it is alleged that snipped-for-privacy@meeow.co.uk spake thusly in uk.d-i-y:
[snip] [snip]I think both of those come down to 'construction methods' rather than wiring per se. A fire which in the UK will result in a smell of hot/burned PVC then a call to an electrician as to why the breaker keeps tripping now, would likely have burned down many homes in the US with the all wood construction.
As to dangers, I think the dangers inherent with electricity often mask other dangers.
As to wiring scenarios permitted but dangerous, to name a few we have ring circuits, which allow the connection of 20A rated cable to a 30 amp circuit protective device. I know in practice they have proved remarkably resilient, but they still give me the creeps. 1x 16A radial per room, using 2.5mm cable with a _full size earth_ (none of this cutdown 1.5mm earth in a 2.5 cable), maybe 2x20 amp radials for the kitchen (on 4mm cable) would make me happier:-)
And 6amp lighting circuits with type B breakers, so that the lights on the stairs go out at random (quite frequent) intervals is odd too.
we have a lot of woodframe here as well, though brick is more popular.
This has been covered in some depth on this ng recently. And the real life stats bear it out: UK 30A rings are no danger at all.
and increase death rates.
yes, it is a bit. Type C gets recommended here, but Bs are still the common choice.
So nothing dangerous.
NT
On 6 Jul 2005 15:07:55 -0700,it is alleged that snipped-for-privacy@meeow.co.uk spake thusly in uk.d-i-y:
[snip]
I thought it had. (I came in at the tail end I believe).
Indeed not, I just don't like them very much:-)
How would that increase death rates?
Type C is good yes.
I keep thinking "halfway down the stairs when the lights go out" or "carrying a pan of boiling water across the kitchen"
So you don't understand the principles of final ring circuits?
Why would lights go out at random on the stairs?
On Thu, 07 Jul 2005 00:00:28 +0100,it is alleged that "Dave Plowman (News)" spake thusly in uk.d-i-y:
Yes I understand the principle. I just don't *LIKE* the principle.
Because type B 6 amp breakers often trip whenever a lamp blows on the circuit.
You don't seem to understand why the CPC size can be reduced.
Still using mains filament lamps in 2005? It really is time to move on...
I've never had an MCB trip "randomly" or even on a bulb blow.
That is why I have an emergency lighting unit in the kitchen-dinette-study-lounge.
Owain
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