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The Sunday Salient..........Quiz.

Zoomup
Biblical references will instantly disqualify any entrant, so there, be warned, we don't want that nonsense on a Sunday do we?


The I.E.T. opening web site page with the rotating rectangular board has made me dizzy. Is the designer on something do you think? Clicking on it is like duck shooting at a fun fair side stall with a light cork gun and a wind blowing.


Anyway to the Sunday consideration. Where was I? Oh yes R.C.B.O.s, those residual current devices with inbuilt overload protection and a little functional tail coloured cream or green and yellow.


Q.1. Is there any safety advantage in having a separate connection to earth by an independent earth electrode to the main earth terminal for the functional earth tail of an R.C.B.O. for:


a, A TT supplied installation?


b, A TN-S supplied installation?


c, A TN-C-S supplied installation?


Z.




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  • 0
    I think most manufacturers are ditching functional earth tails on RCBOs.


    That said I think there is a strong case for an earth electrode on all installations. The lower the earth resistance the better.


    My reasons are.


    1. The lower the earth resistance the better as is it lowers touch voltages and speeds up disconnection times.

    2. Very handy in the event of a lost PEN on a PME system if you have an EV charging point.

    3. Very handy on a PME installation to prevent fires in the event of a lost PEN. You will need a low earth resistance and a substantial earthing conductor.

    4. Essential in the future when we become Prosumers and we need to operate our own generation system in island mode.


    The Germans are big on Foundation earthing (FE) and have implemented it since 1966. House builders, and other buildings, build in foundation earthing at the construction stage and look to get the earth resistance down to less than 10 ohms. The foundation earthing is installed and tested for continuity by electricians before the concrete is poured. The Germans use a DIN standard for this work, an interesting read if you can get hold of a copy. And yes before you ask they have PME earthing systems.


    There is a first mention of FE in the 18th Edition that can be found at 542.2.3. It is used in large buildings where the re-bar is picked up to give an HV/LV global earthing system. Also in railway premises. 


    There is an issue with a lost PEN if you are the only one in the street with a low resistance FE and a PEN goes open circuit as you are going to get most of the diverted neutral current. If everyone around you has a FE then you will be OK as you will have "heard immunity". Note this is the first time anyone has used this term in the electrical field. I claim copyright on this along with my first use of the terms "doorstep competency" and "unicorn device".
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  • 0
    I think most manufacturers are ditching functional earth tails on RCBOs.


    That said I think there is a strong case for an earth electrode on all installations. The lower the earth resistance the better.


    My reasons are.


    1. The lower the earth resistance the better as is it lowers touch voltages and speeds up disconnection times.

    2. Very handy in the event of a lost PEN on a PME system if you have an EV charging point.

    3. Very handy on a PME installation to prevent fires in the event of a lost PEN. You will need a low earth resistance and a substantial earthing conductor.

    4. Essential in the future when we become Prosumers and we need to operate our own generation system in island mode.


    The Germans are big on Foundation earthing (FE) and have implemented it since 1966. House builders, and other buildings, build in foundation earthing at the construction stage and look to get the earth resistance down to less than 10 ohms. The foundation earthing is installed and tested for continuity by electricians before the concrete is poured. The Germans use a DIN standard for this work, an interesting read if you can get hold of a copy. And yes before you ask they have PME earthing systems.


    There is a first mention of FE in the 18th Edition that can be found at 542.2.3. It is used in large buildings where the re-bar is picked up to give an HV/LV global earthing system. Also in railway premises. 


    There is an issue with a lost PEN if you are the only one in the street with a low resistance FE and a PEN goes open circuit as you are going to get most of the diverted neutral current. If everyone around you has a FE then you will be OK as you will have "heard immunity". Note this is the first time anyone has used this term in the electrical field. I claim copyright on this along with my first use of the terms "doorstep competency" and "unicorn device".
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