Earthing and lightning protection

[Timlouth]

Are you allowed to connect lightning protection to earth bonding system.
I work overseas and haven't got any reference books to check the 17th edition rules but I would have thought it to be a potentially dangerous practice.
I thought I had better check the facts before I tell our contractors to change it.

Many thanks.

Tim.

 

[Spark123]

Yes, the lightning protection system is one of the items which needs to be connected to the MET. The red book says the bonding needs to be in accordance with BS EN 62305, not got a clue what that BS EN says!

 

[NotHimAgain]

This is a moving target.

It used to be no.

Then it was yes if all the other standards agree.

From 1 September when the new BS EN 62305 comes into full effect, it will be yes/no/maybe

An assessment has to be carried out of the locations of down conductors in relation to internal electrically conductive building services. This helps to determine bonding and surge protection requirements.

Its rapidly become an 'experts only' area.

 

[333rocky333]

http://www.furse.com/elp/howtolp.htm

 

[holmslaw]

..

 

[NotHimAgain]

Lightning protection has to be connected to the main earth terminal - its been in the regs for years.

Take a look at 411.3.1.2 - I think you will find things are bit different now.

 

[holmslaw]

..

 

[NotHimAgain]

It says connection shall be made in accordance with BS 62305. This standard requires you to carry out an assessment of the relative locations of the lightning protection down conductors and any conductive building services. In some cases this assessment will indicate that you should not bond to the lightning conductor.

 

[holmslaw]

..

 

[NotHimAgain]

It has always been the case that, if possible, we should keep our electrical installations separate from lightning protection systems. Quite simply to avoid having the energy from a lightning strike reeking havoc in our installation.

So in an ideal world you would not bond the systems together and that is how it used to be.

The trouble is if your lightning system comes 'within range' of you electrical installation, either directly or via some bonded item like the steel structure, it will jump in and reek havoc anyway. This can set up dangerous potentials between the lightning system and, say, extraneous-conductive-parts. If you bond the systems together you can usually reduce these potentials to a safe value.

It now appears that we must decide what to do after an assessment. I don't have a copy of BS 62305 - which comes into full effect on 1 September - so I am working off articles in the technical press etc. It would appear that in, say, some timber framed buildings bonding may not be required or advisable. Its all getting very complicated - time to retire I think .