Friday, March 12, 2010

Lightning roof conductor installation

This post shows a few pictures of an adhesive type of clips for installation of the roof conductors of a lightning protection system to a building’s metal roofing system.

Picture 1 – Method of fixing of air termination conductor network at a roof area



By design, the function of the air conductors is to present at the highest points of a building structure an area that will attract the lightning strikes away from other parts of the building.

The surge current carried by the strike will then be routed down through the down conductors to the earthing or what is called lightning rods at the ground level or the lowest level in multiple basement structures.

You can see pictures of the lightning rods at this post, Lightning earth rod pictures.

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The Design

The purpose of the design is to create a network of conductors so that no point on the roof is more than five meters away from the nearest conductor of the network.

Where part of a roof structure is raised above general the roof level of a building (e.g. lift motor room), then that part of the structure shall have its own roof conductor network.

This upper air termination network should again be properly bonded to the air terminals of the lower roof, and to the overall building’s lightning protection scheme.

In order to have all points on a roof not more than 5 meters away from the nearest air terminal conductor, the British Standard recommends that a grid of 10m by 20m meter is used.

For high-risk building like explosive stores, the grid requirement is tighten to 5m by 10 m grid.

The Installation

As you can see, in general, the design of a lightning roof conductor network is relatively simple.

Just create a 10 m by 20 m grid (or 5m x 10m) of copper tape throughout all roof areas. Usually that should be good enough for the air termination network.

The vertical terminals (some people call them “vertical finials”) can be installed but as far as I understand it the experts of lightning protection systems have divided opinions about whether the vertical terminals would actually improve the effectiveness of the air termination network.

I know of a government department who forbid the use of the vertical terminals on all their new projects. The reason is simple.

“Why would we want to attract the lightning to our buildings?”

Good point.

Now how do we install the roof conductors? I do not have that many digital pictures on this yet, so I hope what I uploaded below can be of some help to those who need them now.

You will see more pictures on this in the future. The problem I have is that I never thought I would ever need all these pictures of electrical installation works. So I never keep any personal collections of them.

Only now, with the invention of blogs and their related mediums, that realized the mistake of not keeping my own collections of the photographs.

Okay, back to the pictures.

Diagram 2 shows a simple cross section of lightning protection and the roof conductor and Picture 3 shows how a roof conductor is fixed to the parapet wall at the roof level.

Diagram 2 – Simple cross section of a lightning protection system



Picture 3 – Installation copper tape with copper clip



When the roof is a flat concrete roof, the installation of the 3mm x 25mm copper tape is quite simple. The copper clip as shown in Picture 3 is usually good enough. Many engineers prefer a saddle so the copper tape is raised a few millimeters above the surface. That is just a matter of preference.

However, when the installation is on other type of roofing systems, then the method of fixing is usually more difficult.

Problems with the installation of the roof conductor network

With the popularity of the new technology of lightweight all-metal roofing system, questions often arises whether the whole metal roofing system can be bonded to and form part of the lightning protection system without the need for a separate air terminals.

Theoretically "Yes", these metal roofing system scan be used as the air terminal and they have been practically installed to also serve that purpose for a while, even though in many cases the air termination network are still installed as a precaution.

However, the development in the metal roofing system has resulted in the use of very thin roofing sheets that they require some form of metal parts to hold them together and to the roof structure.

The effect is a complete isolation of a sheet from the adjacent one, and to the roof structure.

In these cases, it is necessary to install a separate aerial conductor network

However, fixing the lightning copper tape to roof metal sheets can be difficult or costly to implement. I have had a lot of problems with fixing the roof conductors to metal roofs in the past.

That is the reason I write this post.

I have not been dealing with the installation of the roof conductors for quite a while. However, recently I found out that manufacturers (at least FURSE has it but I haven’t checked with other manufacturers yet) now already has an adhesive type of clips that make the installation of the air terminal network a piece of cake.

The following pictures show the copper tape installation using these clips.

Picture 4 - The adhesive clip installed at vertical position



Picture 5 - Adhesive clip component



Picture 6 - Underside of the adhesive part with adhesive protection



Picture 7 - Installation work of lightning roof conductor network in progress



Picture 8 - Compression joint for 3 mm x 25 mm lightning copper tape conductor



Picture 9 - Coil of 3mm by 25mm lightning copper tape conductor




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1 comment:

Keystone Contracting Corp. said...

Metal roofing is a lot more durable then the average asphalt shingle type of roofing. It is the strength of the metal that counts.

-Keystone Contracting Corp.
Brooklyn Roofing Contractor