general testing questions

[Chr!s]

Yes you get a lot of differing of opinions between organisations, i think sometimes the help desks are unsure when it comes to design,not all, if they dont have a full understanding you tend to get conflicting opinions.

 

[Chr!s]

but that does not really answer the q. my take is that if the bonding conductor is capable of withstanding the likely fault current for an excess of 0.4 secs. then it is adequate. but would you replace 6mm with 10mm regardless?

Well you would need to take into account the supply earth impedance and the impedance of any extraneous conductive parts in parallel.

Normally in TT and TN systems little current flows in the bonding under fault condition (unless a broken Pen).

 

[pushrod]

The other point is, if this was the case then why in 701.415.2 refer you to 415.2.2 for the effectiveness of main bonding?

.

Mind the whole of this section (701.415.2) is entitled "supplementary equipotential bonding" and (iii) at the bottom of it says "all extraneous-conductive-parts of the location are effectively connected ... then there is the note referring to 415.2.2 for the assessment of whether parts (rather than a part) are effectively connected to the MET so it could be meaning that they are supplementary bonded and not actually be meaning the mpb, hence the reference... ?


I think the colleges should be saying to their prospective students you need 4 good GCSEs grades A to C, one of them must be science, it would be useful to for one to be maths, oh and of course you must have a degree in English to understand the regs

 

[Chr!s]

Mind the whole of this section (701.415.2) is entitled "supplementary equipotential bonding" and (iii) at the bottom of it says "all extraneous-conductive-parts of the location are effectively connected ... then there is the note referring to 415.2.2 for the assessment of whether parts (rather than a part) are effectively connected to the MET so it could be meaning that they are supplementary bonded and not actually be meaning the mpb, hence the reference... ?

Well the final section refers to omitted supplementary bonding, where the connection from the extraneous to the met meets 415.2.2.

So if you have a extraneous pipe that enters the location then you would bond it back to the met, its effectiveness it met by 415.2.2.

415.2.2 actually says between the exposed and extraneous parts, which would take into account R2. But seeing how we have ommitted SMB we are in fact testing MPB using the method in 415.2.2

 

[Chr!s]

If the 0.05 is there for volt drop in reference to touch voltage, which reg?

And all these circuits with reduced cpc are in trouble where the supply impedance is low

 

[pushrod]

Who can tell, maybe the next edition of the regs will make it clearer or an updated GN 8, think that one is still in the 16th.
One of the best things about this thread, that maybe a few other posters could learn from, is that there has been people taking opposing views and arguing their case but never once has there been a derogatory comment...




- i'm waiting for one now

 

[telectrix]

no comment. still licking wounds after being undercut on what would have been a nice job

 

[Chr!s]

Spoke to IET the other day, now Richards colleague has a differing opinion. He agrees with what ive stated and agrees some clarification in the new GN3 would be useful.

Ive also sent an email, but no reply as yet.

 

[pushrod]

Spoke to IET the other day, now Richards colleague has a differing opinion. He agrees with what ive stated and agrees some clarification in the new GN3 would be useful.

Ive also sent an email, but no reply as yet.

Yep the old 2 answers thing again lol at least it is a fairly minor point i suppose. I still have not had an answer to my 2nd question either. Be very interested to see what they reply to you. Maybe they are all going to go down the pub and have a chat about it

 

[Chr!s]

Yep the old 2 answers thing again lol at least it is a fairly minor point i suppose. I still have not had an answer to my 2nd question either. Be very interested to see what they reply to you. Maybe they are all going to go down the pub and have a chat about it

You wont be far wrong there, as for the 0.05 Paul could not give a definitive answer other than its a test between two points and shows a good sound connection.

 

[pushrod]

Hi Chris,
Well at least he didn't contradict himself. Sounds a bit like they have still not decided but pretty obvious that your points are all valid so well done to you in seeing the inconsistency of the arguements. Be interesting to see what they come up with in a new GN3, mind i don't think they have even published a GN8 to the 17th, so no idea when a review of a 17th updated one will be lol

BTW I never even received a reply to my email asking about the origins of the 0.05Ω value and how it was calculated

regards Pushrod