Of course it would require IR testing between Live / Neutral conductors and the MET. That testing is the same as IR testing between Live / Neutral conductors and the CPC test which as I understand it are part of routine testing.
Supplementary Equipotential Bonding Q
- Thread starter CEC
- Start date
Of course it would require IR testing between Live / Neutral conductors and the MET. That testing is the same as IR testing between Live / Neutral conductors and the CPC test which as I understand it are part of routine testing.
Sponsored Links
I'm not sure I understand that - since, as you go on to say, since the metal stud work was floating, there is no insulation test that could have detected the problem.
It was, but this was an exceptional and very unfortunate situation. You now seem to be extending the argument to all non-accessible/touchable metal in a building. Are you suggested that that should all be earthed - and what about metal screws and other fasteners which penetrate a wall?
Kind Regards, John
I fully accept that nails and screws go into unseen cables and become Live and they may then connect with a metal item such as a shelf bracket which becomes Live. It would be impractical to prevent this by bonding. Hence the requirement to "protect" concealed cables less than 50 mm from the surface with an RCD. There should be a regulation that advises that screws longer than 45 mm should not be used for fixing metal things to walls.
Incoming supply pipes have to be bonded in case a non conductive supply pipe tries to import a dangerous potential into the equipotential zone that exists inside the house. What chance is there that a non conductive supply pipe will import a dangerous voltage with an impedance low enough to allow a harmful current to flow. ? I would say that chance is very snall.
What chance of the insulation of a cable threaded through a metal structure becoming abraded and a conductor making contact with the metal structure ? Assume that has happened but gone un-noticed, ( as in Miss Shaw's flat ) The door plate of a door lock could be screwed to that Live metal stud work. When the door is closed the door handle could well be Live. Harmless ? Earthed metal light switch operated while opening the door with the other hand.
Chances, risk assessments, adverse events happen and rules are changed as a result, some changes are knee jerk and create other problems. Other changes are considered too expensive to impliment given the near zero chance of that "something" happening.
Not all events are recorded, fatal accidents are recorded, most accidents in commercial / industrial premises are recorded. How many incidents in domestic premises are recorded and reach the attention of those who write the regulations ?
Quite so.
Yes, IF the cable is in a 'safe zone'. If not, then an RCD alone is not regarded as adequate 'protection'.
It would be nice to think that screws longer than 45mm could be outlawed, but what 'regulations' did you have in mind? The 'Wiring Regulations' are clearly not appropriate, but if the requirement was hidden away in some dusty corner of the Building Regs, I would imagine that the great majority of people who put screws into walls would not even be aware of the requirement. Furthermore, today and for a good few decades to come, there are going to be many cables buried far less than 50mm deep in walls.
What???
Again, an extremely small chance, I would say - but I must again ask, are you suggesting that there should be a requirement for all concealed metal to be earthed?
Indeed, and there is no obvious solution to that problem. In these situations, one generally has to rely largely on 'informed common sense' to assess the likelihood of various theoretically possible scenarios.
Kind Regards, John
Sponsored Links
Do you mean "bonding" - i.e. connecting to other metal parts so that the shelf bracket would have no potential difference wrt the other metal parts, or
do you mean "earthing" - i.e. connecting to the MET via a CPC so that an OPD would disconnect the supply?
There could.
Is that the reason?
That depends on the answer to the previous question.
I presume it should be very little.
... but how many of the above have happened?
What are you saying? Blue Moon occurrences cannot be guarded against if the result is more dangerous.[/QUOTE]
As you probably realise from my previous comment (in response to bernard) I am struggling to understand how "a non conductive supply pipe" could "try to import a dangerous potential into the equipotential zone".
Kind Regards, John
- Joined
- 26 Aug 2016
- Messages
- 6,833
- Reaction score
- 1,010
- Country
I think he meant conductive, and there's indeed a high chance indeed that it could import a dangerous potential (ie earth) into a pme equipotential zone.
No I meant non conductive
I consdered that, but he repeated "non conductive" again in the next sentence as well, so I really don't know what he was trying to say!
Is he perhaps again getting worried about the conductivity of the water (assuming what is being 'supplied' is water, rather than gas or oil)??
Kind Regards, John
It can't ( other than a few micro amps through water in a water supply pipe. ). So why bond it ? And with 6 mm² or 10 mm² copper in some cases ?
There in no requirement to bond something which is not an extraneous-conductive part.
The regulation about the siting of main bonding is totally confused/confusing, seemingly written by someone who had no idea about the concept and purpose of main bonding - but that whole reg only apllies WHEN main bonding IS required, and that's only when one is dealing with something which IS an extraneous-c-ps (and hence excludes pipes which enter the premises in plastic).
Kind Regards, John
- Joined
- 26 Aug 2016
- Messages
- 6,833
- Reaction score
- 1,010
- Country
Yes not to mention that you have to bond gas just after the meter, regardless of whether the meter is inside or out and where the conductive part entered
Or water (if there is a meter there). However, I think you're making the same mistake as bernard. That crazy regulation (which, IMO, is probably best ignored - whatever BAS might say about ignoring regulations!) about 'where one should bond' only applies IF main bonding is required - and there is never a requirement to main bond something which is not an extraneous-c-p.
Kind Regards, John
No it does not say that -
it only say after the meter, which is WRONG electrically, when internal, but
at the point of entry when external.
Oh - I realise you mean that when external the point of entry is after the meter - but
that would be correct IF, as John said, it IS an extraneous-c-p.
that would be correct IF, as John said, it IS an extraneous-c-p.
DIYnot Local
Staff member
If you need to find a tradesperson to get your job done, please try our local search below, or if you are doing it yourself you can find suppliers local to you.
Select the supplier or trade you require, enter your location to begin your search.
Are you a trade or supplier? You can create your listing free at DIYnot Local
Sponsored Links
