Why do "builders" seem to think they are technically competent to design and install services? I've lost count of the number of defects I've encountered with gas, electrics, water etc. Enquiring of the householder often elicits the reponse "oh the builder installed it that way as he couldn't get a sparky/plumber/gas installer etc when he was doing the extension etc.
circuit
Definitely, I'm not saying they should either, hence my last point.
The up-to-date rating for 'clipped direct' conditions T&E is 20A, not
19.5, see Table 4D5A. The up-rating took place in Amendment no. 1 to BS 7671:2001, released in 2002, seeFrom the aforementioned Amendment:
"433-02-04 For a ring final circuit protected by a 30 A or 32 A protective device complying with BS 88, BS 1361, BS 3036, BS EN 60898, BS EN 60947-2 or BS EN 61009-1 (RCBO) and supplying accessories to BS 1363 and wired with copper conductors, the minimum cross-sectional area of both phase and neutral conductors is 2.5 mm2 except for two-core mineral insulated cables to BS 6207 for which the minimum is 1.5 mm2. Such ring final circuits are deemed to meet the requirements of Regulation 433-02-01 if the current-carrying capacity (Iz) of the cable is not less than 20 A, and if, under the intended conditions of use, the load current in any part of the ring is unlikely to exceed for long periods the current-carrying capacity (Iz) of the cable."
This clearly makes it impossible to design a compliant ring in 1.5mm^2 PVC T&E cable.
The condition causing greatest fire risk is if the cable CPC (earth) is not adequately protected in the event of an earth fault. The combination of a 30A rewireable fuse as the protective device and the old 2.5 T&E, which only had a 1mm^2 CPC, can cause this situation to arise for rings over a certain length if the supply Ze is toward the upper limit. An earth fault occurs, there's not enough current flowing to blow the fuse quickly, the cable CPC overheats and possibly catches fire as it protects the fuse.
Thus it was realised sometime around the late 70s that lots of inadequately protected rings had been installed. BS 6004 was amended to require a 1.5mm^2 CPC.
Moral - never re-use old 2.5 T&E cable, at least not without checking the CPC size.
Mr Cranium rambling again.
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He never denied it when confronted.
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Obvious, that is why 2.5 is standard. Some turkey named Jerry says it has to be 10mm. Yes, 10mm cable in a ring main.
Only on the Internet you get this.
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I hope not. Modern lighting uses a lot more power than in the old days and
1.5mm isn't that much more expensive.IMHO 1mm stuff is only suitable for fire alarms and so on.
A 3kw kettle will work fine off of 1.5mm cable, it's capable of handling
3.6kw.
Thinking about it you're right I have got it wrong, 10mm indeed (!), probably more like 30mm....
IMM, it's you who plainly don't know what a RING MAIN is and how different it is to a RING CIRCUIT (or ring final circuit) - for one, a 'main' is normally out in the road and a 'circuit' is in a building !
He didn't need to denied it, the point that you removed the qualifying statement and in so doing you were able to twist what he said.
1mm can safely carry 10 Amps, and as most lighting circuits are protected by a 6 amp fuse/mcb, 1mm is quite safe to use.
Will it handle the 3kW electric fire as well, and TV?
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Let see, 3kw fire + 3kw kettle + 1000w TV = 7kw.
So a 1.5mm ring would be capable of handling 7.2kw.
Yes.
device
1.5mm^2Right, though they can be made perfectly safe by fitting a 20A mcb.
NT
On Thu, 3 Feb 2005 19:24:29 -0000, "Doctor Evil" strung together this:
We're not on the internet, which you probably already knew as you allegedly invented TCP\IP and everything thereafter.
Rated to that, its capable of a lot more.
And I've never seen a 1kW tv before! Even all valve colour dropper resistor sets came nowhere near that.
NT
-- snip drivel
Wire size determines temp rise, and permissible temp rise depends on insulation material, as well as what safety margins are applied. So in the days of rubber wiring, wires were thinner, and often got warm.
Go back further, and some wires ran positively hot, and it was considered normal. In the 50s hot wiring on a then old installation was just accepted many a time.
I wonder what size Edwardian steel wiring was?
Snowdrops can be deluged by rainfall.
NT
I was just using 1kw as an extreme example, As not sure what every TV's requires.
It can safely carry 10 amps on its own. Unfortunately cables nowadays seem to be grouped together in bunches, stuffed along RSJs and tacked in a myriad of other unsafe places. I know this because I've just ripped out the wiring from a house that was completely rewired in the 80s and the number of burnt bits of insulation was eye-opening. How the place hadn't burnt to the ground I don't know. Using 1.5mm allows more underrating and is safer for little extra cost.
A few more people not cutting corners in the past and we wouldn't have been lumbered with Part P.
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