Lightning Protection for Chimneys

The insulators hold the flat in place without the need to drill and therefore doesn't reduce the CSA.

dear,

In this case , the % of lightening stroke flowing inside the structure / building shall be more. definitely, these cosmetic insulators if height- 50 - 60 mm, it with stands the part of lightening stroke, allowing less surge currents to flow inside the structure, minimising the risks of damages due to leakege currents during lightening.

May be damaged insulators might have performed the Z catagory protection !

Well! Between the spans of these cosmetic insulators, the insulation between the structure & the down conductor is air at atmospheric pressure. Even though the insultaor might just withstand - which, I doubt, the potential rise during a lightning stroke, definitely the air insulation would not withtsand and there could be hevay flashover.

Reference is also drawn to Figure 12 of IS 2309, wherein the down conductor is cliped on to a brick chimney wall without any insulator - cosmetic or otherwise. And, vide Clause 12.5.1 of IS 2309, bonding is recommended rather than isolation, when a conductor is run on a structure.

As regards a metallic chimney, reference is drawn to Clause 12.5.3 (b): "where a structure is simply a continuous metal frame, it requires no air terminaltion or down conductor"

Since you are from India, I suggest you read the Indian Standards, before countering any answers which I quote from the Standards.

Good one, EE65.....

And harry, please. For God's sake.
Stop calling the whole word "DEAR" ... restrict it to those who are in relationship with you..

dear,

cool down buddy....

some times hot discussions requires cooling .....

Dear,

This is not the issue with metal structure - this is for RCC structure.

If there is a flash over in between the conductor, better check the Earthing quality of the earth electrodes.

It is established universally that even a good quality earth provided to the lightening conductor, there will be a leakage of electricity in side the building strucure - & thru this, to electronic equipments like intercom etc.. get damaged by lightening surge voltages. Many times causing danger to the human life thru leakage currents in the strucure walls - that may pass thru human body in contact.

Concrete armour WILL conduct more of the lightning charge than it (and surrounding concrete) can thermally handle. That would be desastrous for the stucture's integrity. S.M.

I would insulate it. Concrete is more conductive than you may think at high voltage. The large current of a lightning strike could shatter the matrix by suddenly driving off the water.

My mother was almost killed by a chimney strike on a brick chimney. Shattered the mortar and the brick....

The insulation will protect the masonry from the sudden heat as much as from the current.

One other point which you have not asked and has not been mentioned previously:

The Lightning arrestor should be a straight run down the chimney to the earth point with the minimum possible bends and certainly no sharp or small radius bends.

In a lightning strike the current in the arrestor is huge and any bend present a significant inductance. Any bends will result in a high potential at that point and probably a flash-over to any nearby conductor.

the lightning will jump to the re-bar and blow chunks of concrete out of the chimney.

Principally because the lightening conduction is a half cycle 'skin effect'.

So spacing it off the surface is pertinent to protecting the surface - be it 'conducting' at a lesser conductivity, or 'nominally insulating' - like brick or reinforced concrete.

The overarching idea is the 'ground conductor' is cheaper to replace than the structure, or you wouldn't bother.