IEC 60364 Table 48A

AJJewsbury:

ProMbrooke:

AJJewsbury:

There's also a trade-off between conductor size and cost.

Indeed. The simplest (but most expensive) solution would simply to make the c.p.c.s (all the way back to the transformer) 5x the size of the line conductors - that way touch voltages remain below 50V even during a fault (or 10x and 25V if you prefer).


   - Andy.

Thats just one of two other factors. Speed and transformer output drop also play a role in protection. 

My point was by arranging the potential divider keeping touch voltages below 50V (or 25V) during faults you design out the need for any reliance at all on disconnecton times, or indeed voltage droop.


   - Andy.

My mistake, you would correct. However, one still has the issue of incident energy at the fault point.


The beauty of high conductance is faster disconnection and more voltage sag on the trafo's output.  


I've long proposed discarding the emphasis/focal point of earthing and bonding and rather creating a new, third central pillar of source loop conduction theory, which rooted in admittance on the basis of protecting life and property rather than having earth electrodes and connecting metal things to one another.

 

I've long proposed discarding the emphasis/focal point of earthing and bonding and rather creating a new, third central pillar of source loop conduction theory, which rooted in admittance on the basis of protecting life and property rather than having earth electrodes and connecting metal things to one another.

What is "source loop conduction?". How does it work? Or is it just something that The Dr. and Rose Tyler would come across?


B.S. 7671 already covers safety of installations.


Reg. 131.1 "...intended to provide for the safety of persons, livestock and property against dangers and damage which may arise in the  reasonable use of electrical equipment."


Z.


 

ProMbrooke:

AJJewsbury:

AFDDs are soon to be mandatory?

Do you know something we don't?


I know there was a proposal for AFDDs in the DPC for AMD2 - but often such proposals don't make it though to the final version. AFAIK the decision process is still grinding on. If the comments on the BSI website for the DPC about AFDDs seemed hardly supportive.


   - Andy.

Unfortunately yes.


Those making them, as well as their seat in the IEC, have a rather big push.

Big assumption.


In the UK, international versions of the harmonized standards are also put out to public comment, as was the relevant part of HD 60364 for AFDDs. No comments were received, so it's no surprise the HD says what it does.


As a CENELEC member, BSI have a duty to incorporate the technical intent of HDs.


As I said in an earlier post, there are opportunities to get involved, rather than sitting on the sidelines sulking, or throwing rotten fruit.

ProMbrooke:

The IET should investigate actual touch voltages during a fault for various scenerios.   

 

What makes you think there's no information available? Commentary on the IET Wiring Regulations, but far more informative were presentations given by David Latimer entitled Earthing and bonding - what does it do?  presented as part of the IET Tutorial Workshop on Earthing and Bonding Techniques for Electrical Installations (presented at various locations in London, Manchester, Glasgow and Belfast, between March 2005 and September 2007). One seminar digest that contains his paper and slides is ISBN 078 0 863 418372, and he runs through the possible touch voltages (and how to estimate them with and without bonding), and how they relate to IEC 60479 as they stood at the time.


Worth also remembering that, since 1992, it's no longer the IET alone who are responsible for BS 7671. It's joint IET / BSI and the standard is published by consensus. The organisations represented are listed in the front of BS 7671.

gkenyon:

ProMbrooke:

AJJewsbury:

AFDDs are soon to be mandatory?

Do you know something we don't?


I know there was a proposal for AFDDs in the DPC for AMD2 - but often such proposals don't make it though to the final version. AFAIK the decision process is still grinding on. If the comments on the BSI website for the DPC about AFDDs seemed hardly supportive.


   - Andy.

Unfortunately yes.


Those making them, as well as their seat in the IEC, have a rather big push.

Big assumption.


In the UK, international versions of the harmonized standards are also put out to public comment, as was the relevant part of HD 60364 for AFDDs. No comments were received, so it's no surprise the HD says what it does.


As a CENELEC member, BSI have a duty to incorporate the technical intent of HDs.


As I said in an earlier post, there are opportunities to get involved, rather than sitting on the sidelines sulking, or throwing rotten fruit.

Assumption? If you could only grasp what I knew about AFDDs and the stake the pig players have invested in them.


Considering no comments were made, yet folks have plenty of time to discuss AFDDS in the ASCII sphere, perhaps time on the side lines is granted.


BSI has zero obligation to incorporate or do anything CENELEC says in as much CENELEC has any obligation to listen to the IEC. Of course in reality it is as you say, and manufacturers know that as it was their goal all along. This is exactly how systems fail entire populations. To think on ones own is truly the rarest gift in today's world. 


And getting involved in the current system won't change anything. In the United states there are hundreds if not thousand of proposals and organizations working to get AFCIs out of NFPA-70 where each code cycle the proposals are turned down. 


With that said, you do know AFCIs were solely created to mimic the British wiring system?     

 

Zoomup:

Perhaps the O.P. is gathering thesis material and playing Devil's Advocate to stimulate responses?


Z.

Not even close. If technical debate evokes such suspicion, I only say that democracy is doomed. 

gkenyon:

ProMbrooke:

The IET should investigate actual touch voltages during a fault for various scenerios.   

 

What makes you think there's no information available? Commentary on the IET Wiring Regulations, but far more informative were presentations given by David Latimer entitled Earthing and bonding - what does it do?  presented as part of the IET Tutorial Workshop on Earthing and Bonding Techniques for Electrical Installations (presented at various locations in London, Manchester, Glasgow and Belfast, between March 2005 and September 2007). One seminar digest that contains his paper and slides is ISBN 078 0 863 418372, and he runs through the possible touch voltages (and how to estimate them with and without bonding), and how they relate to IEC 60479 as they stood at the time.


Worth also remembering that, since 1992, it's no longer the IET alone who are responsible for BS 7671. It's joint IET / BSI and the standard is published by consensus. The organisations represented are listed in the front of BS 7671.

I'm not finding much from the IET, BSI, CENELEC and the IEC. The IEC talks about various compromises but does not elucidate them. To me its all murky without much in depth information.


Can you link to this presentations?


 

Zoomup:

 

I've long proposed discarding the emphasis/focal point of earthing and bonding and rather creating a new, third central pillar of source loop conduction theory, which rooted in admittance on the basis of protecting life and property rather than having earth electrodes and connecting metal things to one another.

What is "source loop conduction?". How does it work? Or is it just something that The Dr. and Rose Tyler would come across?


B.S. 7671 already covers safety of installations.


Reg. 131.1 "...intended to provide for the safety of persons, livestock and property against dangers and damage which may arise in the  reasonable use of electrical equipment."


Z.


 

Source loop conduction is the idea that high admittance between the line and CPC/metal work at any point that a fault  is capable of occuring can trigger disconnection of the over current device rapidly enough to prevent physiological harm and fire to the property.


Basically a more evolved theory of ADS.


I know BS7671 covers protection of life and property.

davezawadi (David Stone):

I am not an advocate of AFDDs and have been at a number of meetings where they were discussed at length. I have no particular influence on JPEL/64, or the BSI or CENELEC or the IEC, although I have spent a lot of time with AFDDs and written a paper. I agree that they probably will not make a significant difference to the fire statistics, as they have not in the USA as far as I can find out. Have you looked at the front of BS7671? You can see that there are a lot of representatives on JPEL/64 who may have vested interests in selling AFDDs and possibly many other things too. The problem is not a lack of democracy but that ANY vested interests must be declared at all levels and stages. I should state that I have precisely none and my views are not necessarily those of the IET. Do you have any vested interests?

David CEng etc.

Vested Interests? Cutler Hammer bribed the NFPA and had UL create not only a 1699 standard tailored to Eaton's tastes but various studies claiming how arcing was not only behind most home fires but also how AFCIs would slash the number each year. Since day one it was destination science funded by a gamble.