I know what the earth is for. If in a safety situation a device trips and E,N & L are isolate it is the ultimate safety. Why because the earth could be live from a fault elsewhere. isolating all three is the ultimate..
Why not? If all three are isolated there is no problem.
Being to earth, via pipes, the combi protects itself.
Why are you suggesting that the pipes are earthed?
Adam
Doctor Drivel wibbled on Friday 13 November 2009 12:58
I thought your "house" had wall to wall cushions?
;->
Doctor Drivel wibbled on Friday 13 November 2009 13:10
Definitely illegally.
It's hardly much safer on a 20A or 16A radial - or are you proposing every table lamp and wall wart has its own radial? You'd need the whole wall for your breaker panel...
ARWadsworth wibbled on Friday 13 November 2009 13:35
*splat*I'll have to make more coffee now. It's all over the keyboard!
Doctor Drivel wibbled on Friday 13 November 2009 13:18
Not really - we have enough braincells in this house to cope with a sub optimal system for a couple of weeks.
The only real hazard is tripping over leads. That's why you have fusing designed to suit the characteristics of the cables, exactly so you cannot overheat them dangerously in the event of overload. Unless you've been rewiring your fuse carriers with old hacksaw blades...
Doctor Drivel wibbled on Friday 13 November 2009 13:45
The only earth you should concern yourself with is the stuff in your plantpots...
I am following this thread with some interest (and amusement).
I am now confused.
I understood that a radial circuit to have a single outlet, fused appropriately for the job.
I then understood that there was no need for a fuse in the appliance plug.
Now that I have seen mention of a 32A radial circuit with daisy-chain sockets, how can it be considered safe to use un-fused plugs?
If such a daisy-chain is in fact used in real life, I do not see how it differs from a ring - other than it will need heavier cable.
It seems every time you open your mouth, it is only to stick your foot further in. Running a 32A circuit at or near full capacity with a well distributed load is exactly what it was designed for. Not a fire risk.
As I said before they are pros and cons for both circuit topologies. However for general power distribution socket circuits, rings usually have a slight advantage.
Q: Which wire is most likely to be loose or disconnected? A: The thinner earth typically.
Q: What is the most likely effect of a loose wire? A: A high resistance connection, rather than a disconnection.
Q: In which circuit topology is a high resistance earth connection most dangerous? A: A radial
Q: In which circuit topology is a high resistance L or N connection most likely to result in a damaging temperature rise? A: A radial, since the rise will be concentrated at the high resistance point, with no alternate current path to mitigate.
The same applies on a radial if the connection is loose rather than open.
If you see them for sale to the general public in this country, then report them to trading standard.
Just like the US and much of europe then ;-)
(A|s a general point, table lamps are pretty unlikely to cause a significant overload - its hard to find ways of sucking more than a couple of hundred watt out of a BC lamp connector unless you have one of those long since banned BC trailing flex plugs)
It does tend to get a bit surreal with dribble ventures into the world of electricity. ;-)
Not necessarily. Radials can be used with just a single load - this would be typical for dedicated circuits feeding fixed equipment like immersion heaters, cookers, storage heaters etc. i.e. high long term loads.
You can also use a radial for provision of general power purpose sockets. You can have as many sockets as you like on the circuit, but the circuit should not serve more than 50m^2 of floor area.
No, in the UK there is always a need for a fuse in the plug. Sale of non fused plugs is illegal. This is because our socket circuits are typically overload protected at well above the continuous current carrying capacity of the plugs and sockets or appliance flexes.
Unfused plug / socket radials are found in other countries, but current capacity of the whole circuit is typically limited that of the plugs and sockets and appliance flexes.
It can't.
(a radial does not have to be a daisy chain by the way - it can split and branch any place it likes).
That is the main difference. Its well suited to the dedicated hard-wired appliance scenario described above (cookers etc), but is less well suited to general purpose socket circuits in most cases. If you want the same 32A capacity (and a 32A circuit is often of far more practical use than a pair of 20A ones), you need to wire it in 4.0mm^2 T&E which is much harder to work with, and can also cause problems when you want more than pair of cables into a single accessory since the terminals are often not big enough.
Radials are sometimes used for sockets where the particular layout would be awkward to wire as a ring, or there is more predictability in the appliances that will be used in a given place, and also where it is evident at design time that a ring would be poorly loaded (say with a cluster of large loads all concentrated right at one end etc)
We rather suspected that.
Owain
Owain
Les Desser wibbled on Friday 13 November 2009 15:33
It could, but it might be clearer to refer to that as a dedicated circuit rather than a radial. This would commonly be the circuit feeding a storage heater or immersion heater for example.
A standard radial 13A socket circuit (ie IEE definition of standard) may include:
20A radial with many sockets; 32A radial with many sockets amongst other options.
That could be the case. eg I will be using a 45A RCBO to feed my heating system (mostly gas when it exists). This will feed a panel consisting of:
6A MCB for boiler and pumps and control. I might drop that to 3A if I think I can, then, without argument, I can dispense with the 3A fuse on the boiler.Then, 3 lots of:
16A MCB for each back up 3kW immersion heater. These will then not have a switch or a fuse in the flex connection unit as there is no point. I hate having random fuses in odd places. There are times it's necessary, like an FCU feeding some bit of equipment from a ring, but for a properly designed system like a heating system I'd rather dispense with them and bring all protection into a single panel.It isn't. You would never install (eg) a 15A round pin socket on a circuit other than one fused at
I had puzzler last year, an old (single) ring in a semi serving upstairs and downstairs with all wiring between floors and mainly glued down carpets. None of the conductors appeared to be in a ring. Eventually I found a plastered over back box on the landing, with two cables neatly rolled up inside, as left by the first fixers.
Obviously no testing had been done when the house was constructed!
I also had problems with the lighting circuits, an upstairs and downstairs circuit, with the live shared to the landing light from both circuits, due to a miswire in the light switch downstairs. Made interesting results to pulling one of the fuses.
If I'd found the original leccy I'd have used a bt of wire to.......
No way.
An electrician who leaves his first fix cables neatly rolled up!
I blame the plasterers for messing with the electricians work:-)
Obviously. And it only takes basic equipment to show that the ring is complete.
Literally shocking
I think that you would be justified to do so.
Adam
... provided you remember to provide a DP isolating switch, accessible, within 2m of the cooker location, as well as the outlet behind the cooker.
Owain
Owain wibbled on Friday 13 November 2009 21:27
Yes - that's why I mentioned:
"a) The cooker is logically isolated by using the cooker switch, whether gas or electric;"
:-)
But, yes, it is a general requirement that fixed appliances with concealed sockets or hard wired in must have an accessible DP isolator nearby.
What I was trying to do is avoid having two different isolators for a high power electric cooker and a low power gas cooker.
Cheers
Tim
That'd be 6 wires! Oh, OK though as Dr. D can count those on the fingers of
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