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#137080 - 05/25/03 06:56 PM Lightning conducyors  
lyledunn  Offline
Member
Joined: Jun 2002
Posts: 159
N.Ireland
There is a requirement in the UK to bond the lighning conductor to the electrical installations main earth terminal. I cannot see any advantage in this, any comments?


regards

lyle dunn

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#137081 - 05/26/03 02:24 PM Re: Lightning conducyors  
j a harrison  Offline
Member
Joined: May 2002
Posts: 106
southampton, england
Lyledunn,

In regard to your enquiry, i have never had to bond a lightning conductor to the main earthing terminal of any installations here in England,

I will look up the relevant codes in regard to this but i am sure we dont have to,
most of the specialist companies take a lighting conductor staight to the ground, i cannot see any point in linking it to the main earth conductor.
John H


#137082 - 05/26/03 02:35 PM Re: Lightning conducyors  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
Most bonding requirements are to make sure that a mimimum of potential difference can exist between exposed metalwork in the event of a fault (or in this case, a lightning strike).

I have to admit that I'd need to check this point myself, as I've never yet worked on any building with a lightning rod.

Certainly when installing radio masts and such like, I would always securely ground and bond the mast.


#137083 - 05/26/03 03:40 PM Re: Lightning conducyors  
David UK  Offline
Member
Joined: Oct 2002
Posts: 134
Inverness, Scotland
Yes you do have to bond lightning protective system, see Reg. 413-02-02 (vi) in BS 7671: 2001.


#137084 - 05/27/03 02:21 PM Re: Lightning conducyors  
james S  Offline
Member
Joined: May 2003
Posts: 107
West England
I have not came across this myself, but have recently observed a new bank of mobile phone masts being installed in the grounds of my work place and noticed they ran there lightining conductor (which was i noticed, insulated?) straight onto there own earth rod!


Is it a good idea to introduce such high voltages towards an earthing system which is not struck?


#137085 - 05/27/03 03:10 PM Re: Lightning conducyors  
C-H  Offline
Member
Joined: Sep 2002
Posts: 1,497
Stockholm, Sweden
Quote

I have not came across this myself, but have recently observed a new bank of mobile phone masts being installed in the grounds of my work place and noticed they ran there lightining conductor (which was i noticed, insulated?) straight onto there own earth rod!


I think I've seen this too. Alongside the electrical panels on this floor, there are bundles of cables going up to the roof where there are a lot of antennas. Among the wires is a thick green/yellow wire, which I assume is a lightning conductor.

Quote

Is it a good idea to introduce such high voltages towards an earthing system which is not struck?


Despite the fact that ordinary lightning conductors are bare and run close to buildings, they protect the building. I guess the insulation can be there simply to keep people from touching the wire, i.e. not introducing a shock hazard beacause of different potentials.

OTOH, the insulation on the wire can withstand a higher voltage than normal for the very short period a lightning lasts and if the lightning has a good path to earth, it is not going to jump to find another path.

(Personally, I still don't like it. I think the conductor it has to withstand hundreds of kilovolts, something which requires several millimetres of insulation. But then, I'm just a student who doesn't know this field.)

[This message has been edited by C-H (edited 05-27-2003).]


#137086 - 05/27/03 06:45 PM Re: Lightning conducyors  
lyledunn  Offline
Member
Joined: Jun 2002
Posts: 159
N.Ireland
Thanks to all.
Paul, I fully realise the purpose of equipotential bonding conductors as minimising fault voltages between exposed and extraneous conductive parts within the so-called equipotential zone. However, I am not convinced that there is any valuable purpose served in this respect by connecting to the lightning conductor. Equally, on loss of neutral on a TNCS system it would actually be better if the lighning conductor was separated from the MET. In fact imagine that all BS7671 requirements were met and that some guy was about to test the down conductor. So he separates the down conductor from the earth electrode. At that moment a fault occurs in some circuit in the installation which will raise the potential at the MET with respect to earth.The same voltage will appear at the disconnected down conductor with respect to earth. A rareity perhaps but nonetheless a distinct danger!


regards

lyle dunn

#137087 - 05/30/03 10:32 PM Re: Lightning conducyors  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,211
SI,New Zealand
Lyle,
I would not personally use the mains earth as a Lightning conductor Earthing point.
I would instead drive a seperate electrode for this.
The reason for this being, while lightning has a reasonably high voltage, it has an even higher current (500kA) and introducing this level of current into an Electrical system, no matter how good the Earthing connections are, is not really my idea of a good time.


Let's face it, these days if you're not young, you're old - Red Green grin


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