All UK appliances come with fitted plugs and fuses. And if that fuse blows there's a fault. I honestly can't remember replacing one on an appliance.
Of course Mr Average may replace it with the wrong value - but how would going to a radial circuit with MCB but non fused plugs etc improve this - unless there was a dedicated radial to each and every appliance in the house which even you must admit is plainly ridiculous.
Given that CCITT#4 and 5 weren't up to the fast increasing number of phones/faxes/etc, I don't really think they had much choice than to use it.
It wasn't really touted that much for personal desktop to desktop or server links other than for ATM based video - for which it is still extensively used between studios. VoD was seen as the driving application for ADSL originally but governments soon put the kybosh on that. Fortunately for ADSL, people started wanting faster Internet and the technology was quickly adapted, though all the info is still carried within ATM cells.
I don't think changing over to a common socket will cause us too much grief. I would expect our current ring mains system to be included as an addenda to the standard for legacy systems.
Possibly not everywhere, and quite possibly in electrical, but certainly in semiconductors, nanotech, biotech, vehicle systems ...
Count Bluetooth as one of the last of the old way. Agree it was a mess but the new work should sort it out.
That's what the startup says. And the VC replies "not our problem - go make it a standard and you'll get the money"
Soon. Do you have problems with WiFi ? Are you expecting any with WiMax ?
Would it surprise you to hear that the IEE think so too?
The cable ratings we all use are those which allow the conductor temperature to rise by 50 degrees above an assumed-ambient of 20, to 70 degrees, for PVC insulation; or to 90 for thermosetting; or higher still for more exotic types such as mineral-insulated. Dunno about you, but I'm unhappy holding cable that's at 70 degrees, let alone higher.
Now, sensible installers don't plan to run their cables at those sorts of temps continually - they'll reach for the next size up when they see their calcs are bumping close to margin. (Unless, that is, they work for an outfit where all the calcs are automated to the point where they just see a go/no-go; and/or are doing penny-pinching close-to-margin design for house designs to be thrown up in tens of thousands...)
Stefek
What temperature does PVC insulation blacken at ? Seen so many odd bits of this on our renovations.
I don't think so. I've worked for VC funded startups for 30 years and this is not how it works at all.
The international standards bodies are for those with deep pockets, people with time on their hands and a very limited number of players who can't proceed with their business without standards. The semiconductor industry, with which you are familiar is possibly one of those. Equally, being a player in the semi industry is hardly for those with meagre funding.
Industry standards organisations and alliances may just be within the reach of startups.
There a few standards organisations such as the IETF that are reachable by startups. It's interesting to note that the innovation and speed to agreement based on technical merit rather than political compromise or vested interest makes them a great deal more effective as well.
I'm not holding my breath.
Absolutely. Many aspects such as coverage and especially security are a mess.
I think that that is inevitable.
ATM was one of a series of connection-based technologies which has sought to compete with connectionless and packet technologies over the years.
It's interesting to note that they never do.
I wouldn't comment on what BT is specifically doing, but IP transport, convergence and even triple play are moving faster than you might think.
Not 2 ohms; the rise in resistance is, to first order, linear in the
*absolute* temp, i.e. the scale on which 0C is 273, 100C is 373. So if resistance at 20C = 300Kelvin (near enuff) is 1 ohm, resistance at 100C = 380Kelvin (near enough) is 380/300 times higher, which'll be about 1.25 ohm.1.25 times higher, akcherly, assuming the I bit of I-squared-R stays constant (which is a reasonable assumption for a load in a domestic setting - the resistance of the load will be much greater than that of the cable whether at ambient or final-working temp).
The equilibrium temperature is determined by the thermal surroundings of the cable; naturally that temperature is higher in an insulated wall than in free air, which is exactly why cable ratings are lower for situations where the rate of heat loss is lower. But it's a *lower* rate, not a *zero* rate!
No, it won't! It'll come to equilibrium at a higher temperature than if it was in free air (but at a lower temp than if it were in a vacuum - which would allow it to lose heat only by radiation (which is proportional to the fourth power of absolute temp, so again you don't get thermal runaway)).
Nope. It's constantly losing heat to its environment. When the energy being dissipated by the current flowing in the cable is equal to the energy being passed into the surrounding structure (and on from there into the cold, vast darkness of Outer Space, moving us all inexorably to the heat death of the Universe, currently scheduled for 20+ billions of years, subject to frequent revision in the face of new cosmologicl theories ;-) its temperature stops rising.
The increasing-resistance-with-temp effect does indeed mean more heat is produced at equilibrium temp than at the initial cable-at-rest temp. But the current passing is finite, so the heating comes to an end if that finite current is low enough. (If it's not, we just invented the fuse - resistance high enough and melting-point low enough that temp rise exceeds melting point.)
Incidentally, the place in Regs-calcs where we *ignore* losses to the environment is in calculating the heating effect of a fault current - an L-to-E or L-to-N short. That's because the time during which the cable's being heated - and *seriously* heated - is so short (we hope, and establish by calculation): it's more sensible to ignore the losses and treat the wire itself as the only thing that's being heated. We use only the wire's own thermal capacity (amount of energy needed to raise given mass of that material through 1 degree) as the 'where does the energy go' target; and under those conditions, which are called 'adiabatic', we calculate that the current flowing for the time it flows won't take the cable past its limiting final temperature - for PVC that's 140 degrees C. And the engineering simplification used to calculate the resistance of this cable as it heats up is to use the midpoint between the starting temp - which, as cautious practitioners, we take not as ambient but as the fully-loaded temp, so 70 degrees C for PVC - and the final limiting temp.
Back to the ring debate which kicked this off - my point was that there's a small but non-negligible effect which results in the less-overloaded, longer leg taking a slightly higher share of the (fixed) load current than simple consideration of relative lengths of the two legs would suggest. It's not a huge effect: let's say the load is at 0.2 of the way around the ring, and the ambient resistance of the short leg is R, with the ambient resistance of the long leg being 4R. The short leg gets 80% of the current (4R / 4R + R). Let's say the load's enough to heat that leg up from 20 to 70, so its resistance is now 1.2R, while the resistance of the other leg's not gone up by nearly as much, say only to 4.2R (only a quarter as much of a rise, as it's carrying a quarter of the current). Now the short leg's passing (4.2 /
4.2+1.2) = 77.5% - that's a 2.5-parts-in-80 drop, barely 3%. Like I said, not a huge effect, but not entirely negligible.Stefek
Moulded on plugs are now mandatory - What plug would you get on any new appliance you bought?
Would extensions to wiring be done to the old or new "standard"?
In any case you still have not answered the fundamental question - why change from a reliable proven and safe system to an unproven one with no advantages whatsoever for no reason other than "harmonisation"?
Like the French, Latvian, Polish etc legacy systems? I thought we were going to have a mass rewiring for a few billion pounds?
Oh good, I feel much better now.
Err - yes - lots of proprietary "extensions" which only work with same manufacturers kit. Mix things and you end up, as always, with the lowest common denominator.
Of course.
How do you think many houses were heated then? Electricity was the cheapest fuel available.
OK - I'll replace my gas boiler with an electric one. Why should I rewire the house to do this?
Realistically it isn't. Extension leads and appliances cause about
10 times as many fires as fixed wiring (including plugs).
A good question, to which I don't know the answer offhand. It's certainly *above* 70 degrees C, since that's considered 'long-term sustainable' - the IEE says it'll last 20 years at that temp. The 'limiting final temp' for PVC is 140 degrees C - the temp used (as I've droned on about at length in another posting today!) as the don't-exceed-in-the-presence-of-a-short-circuit-fault temp; but that's a temp expected to be touched only in faults, and only for a very short time (5s / 0.4s depending on the class of the final circuit). Google doesn't immediately come up with an answer that I can see.
But you'll get *much* higher local temperatures where there's a loose connection - all that sparking 'n that; and that's the most typical cause of charring at fixtures.
Stefek
Actually, the ratings assume ambient of 30C, with max cable rise of 40C to 70C. If you have an ambient of 25C, you can add 3% to the cable rating. No table value is given for an ambient lower than 25C.
Max working temperature is 70C. If a fault (short circuit) current passes through a cable running at 70C, the conductors are allowed to rise by 90C to 160C, which should not damage the cable. Cable isn't designed to run continuously at such a temperature obviously, but I would imagine it would need to get hotter before it would char, although there's probably a duration related effect too.
Temperature has a large effect on the expected life of PVC cable though. I can't find it on IEE's website at the moment, but expected life of PVC cable at 70C is something like 21 years, and at 30C it is over 1000 years IIRC.
Opps put in the wrong figures. Not that it matters in this case.
No actually. The load is the same on the end of the circuit and not effected. Even doubling the resistance of the cable has little effect on the current flowing. It does not significantly lower the current it only increases the power disipated in the cable.
Its an insulated wall. What if it uses the same insulation as the space shuttle? Its pretty close to perfect.
Maybe not as *any* cable would melt then. What is the U value for an insulated wall? What value is needed for the circuit to be safe? What is the best U value you can get?
The insulation burns before the copper melts in practice. I know as I have seen copper wire glowing from excess current. The PVC had long gone.
True but not really relevent.
As a generalisation that is true. But not in every case. You make the assumption that both legs are in the same environment. Often they are not.
Coal was the cheapest and was widely used.. evidenced by the smog.
Not only that, the most dangerous aspect of British plugs (the aspect that dwarfed any others in fact) has been removed from the equation for many years now.
The aspect in question? Letting Joe public wire the things!
Stefek Zaba wrote: There's a fine quote somewhere about
or "Any fool can build something for a £, you need an engineer to do it for a penny!"
The Chinese are not going to waste money on increasing the living costs for their people unnecessarily. So by all means go for EU gold plated standards and watch your population become even less competitive (and relevant) in the global market place. ( Those that haven't already left Europe already anyway.
Regards Capitol
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