well what can I say! I saw this thread a good few days back but didn't look at it as i thought that it would be boring, how wrong was I! its been a very entertaining read buts its been one of those that you don't know whether to laugh or cry, and since I haven't posted in a while here's my tuppence worth
Mr cockburn if you are still reading this thread then you really need to go back to basics and learn electrical principles, I know that you may be thinking that people are just getting at you but to be brutally honest your book is errorous and really should be taken out of circulation, you have been corrected on a number of occasions but you fail to acknowledge the fact.You state
One last thing:
I am the proud owner of a set of City and Guilds qualifications that all have something in common apart from the fact that they all bare name, they also include the phrase "no higher grade can be achieved in this subject".
sorry I disagree, I too passed my 16th edition but then had a change of career in 2007 (still electrcally involved though) but I still took my 17th last year because
a)you never know what is around the corner and
b)its a higher grade than the 16th because its up to date
you wanted debate so consider this quote of yours
If in future years somebody comes up with a way of automatically disconnecting the supply, based on the capacitance of the human body then we will no longer be reliant on eebads. But at this point that seems unlikely, therefore we are stuck with it. For one thing it is the only method of protecting ourselves from 400v phase to phase contact,
you have already been told that earthing does not (and can not)protect against phase to phase contact, how can it? its connected,along with the neutral to the star point of the sub-station transformer so it is the same principle as a 110v site transformer ie its a centre tapped connection at its best
I dont agree with the first statment either as ideally someone will come up with a foolproof method of insulation that would negate the use of "earthing", it is extremely difficult to guarantee perfect insulation from earth especially on the supply side which is the very reason that it that we tie one side of the supply to it
it has its flaws but its the lesser of two evils, here is an example
Therefore first test an RCD with a ramp tester to ensure that it is working at 30mA, then go upstairs, take off your boots, lift the carpet and stand on the floorboards, then take the front off of a socket and put the back of your index finger onto the live conductor.
I very much doubt that the RCD will trip and it will hurt like a son of a ****.
Once you've done this, then come back and debate me over whether or not you think you need earthing.
ok here is your debate, apart from the fact that in the statement above, the use of earthing/bonding to any standard makes no difference whatsoever on the outcome (so I can't fathom what your point was) i will use your 'test' as an example anyway
you have two choices
a)take off your boots, lift the carpet and stand on the floorboards, then take the front off of a socket and put the back of your index finger onto the line conductor (or live conductor if you prefer to call it that).
or
b)touch a radiator that has been installed with plastic piping but bonded as per your illustration with supplementory bonding to earth potential with one hand then take the front off of a socket and put the back of your other index finger onto the line conductor
whats it gonna be dave a or b? I'd pick (a)
can you see what your earthing arrangements have done in this scenario?
Once the continuity of copper pipes is removed, the radiators simply become lots of individual extraneous-conductive-parts.
No they don't - they
stop being extraneous conductive parts.
b.a.s is correct you know and reconnecting plasic piped rads to earth potential turns them back into extraneous-conductive-parts
but................heres the flip side
imagine the same radiator in plastic pipe somehow physically coming into contact with a line conductor, would you now prefer
a)it to be connected to earth potential so the fuse/mcb operates quickly
or
b)not connected, so its at a potential difference with the floor waiting for you to come along and touch it
This is where the flaw lies, in the first example its better if the rad is not supplementary bonded in the second it is better if it is, so what do you do?
answer you use common sense and decide on which scenario is most likely to happen and which is most potentially dangerous and regulate to suit
you keep going on about RCD's and earth arangements to 17th edition standards and you have been told that the latter is the same and it is
If it is the fact that you can leave out supplementary bonding if all circuits are fed via RCD that bothers you then I suggest you go and take the exam and get a copy of the book
you still have to verify and measure earth resistance and proceed as necessary
RCD's / RCBO's are great, not only to they offer protection they also to some extent act as insulation breakdown monitoring devices,
Is it the simplicity of electrical safety earthing that is annoying you so much?
Once upon a time heating systems were tubed in copper pipe, if the copper pipes are removed why don't you just replace the continuity that they provided with copper cables?
When you boil it all down, that's all that this is about.
why would you want to connect something that is now isolated from the suppy back to one side of it?
If somebody wishes to demonstrate that the supply will be automatically disconnected whenever an un-earthed extraneous-conductive-part comes into contact with a live conductor, then I will be forced to change my opinion of the 16th Edition.
un-earthed extraneous-conductive-part?
no such thing,it makes as much sense as "a conductive insulator"
as already suggested have a read of the definitions,
I think you mean un-earthed conductive part ie metal window frame? and why would you want to bond that?
Therefore if this 'touch voltage' emerges as a result of the exposed or extraneous-conductive-part that you are in contact with, coming into contact directly with a live conductor and therefore becoming hazardous live itself.
If it is bonded to earth you will be in 'indirect contact' and the supply should automatically disconnect.
If it isn't bonded you will be in 'direct contact'!
no you will be in indirect contact in both cases
again read the definitions in your book
The problem here, is that YOU DO NOT UNDERSTAND the very subject that your book claims to explain.
Oh, sorry, I must be wrong. It must be me, the IET, the contributors to this and their forum... in short, anybody but you.
Look. EVERYBODY DISAGREES WITH YOU.
count me in too ding, he also doesn't understand plumbing systems either but I can't be bothered to go into that
Matt
