Locations for Lightning Arrestors

Santhosh,

IS 2309 gives the guidelines for lightning protection of facilities/ structures.

I believe by lightning arrestor you are refering to the lighting rod used as an air temination systems. This rod is to be provided on top of the building. The number of rods to be installed on top the the building is determined by the area of the roof which is subject to a lightning strike. These rods in turn can be connected to each other in a ring by use of copper strips. The air termination system has to be connected to the general mass of the earth through the down conductors and connection to earthing rods or to a main earth grid provided for the building.

Current Maarey

Good one.Thanks

It is generally difficult to get IS books.

Whether earthing strip is required from lightening arrestor to earthing pit for steel chimney of boiler? or it is enough to connect chimeney bottom to pit.

Ratnagiri,

The steel chimney of a boiler can be used as a down conductor. The steel chimney bottom need to be connected to the earthing system at least at two different points. Ensure that the electrical continuity of the chimney from the point the lightning arrestor is physically connected to the chimney to the earthing connection to ground.

thank you very much.

Is there any detailed information like the distance of placing the rods are the best way of placing them of arranging them.

The choice of positioning of the air termination system on the building is defined in the IS. Normally for flat structures with large area it is preferred to have a metal (copper) strip to be laid on the roof forming a mesh. The rod is generally preferred on buildings/ structures with smaller area.

The exact mesh size/ number of rods have to be worked out based on the building design and risk assessment carried out for the lightning protection.

You need to go through the IS to decide the same or higher a local electrical consultant who has been carrying out these designs in the past.

You can purchase the relevant IS - 2309 from either the BIS or their authorised agents selling the standard.

In Delhi the same is available with Jain Book Store in CP i.e.e Rajiv Chowk.

Thanks for a neat diagram Nigh and great explanation one that Faraday may agree with. Standards and legal requirements for lightning protection will vary between countries but perhaps you wont mind if I share a little that I have seen.

During the construction phase when a structure is still at ground level, points are chosen at around 50m apart usually at the base of a support column. A copper rod is driven into the ground at each point and the resistance to earth measured to make sure that it meets a minimum requirement perhaps 50 ohms. If not, another section is added to the rod which is then driven deeper into the ground until the resistance meets the minimum conductive requirement to earth. The support column's reinforcing is then attached to the copper rod at that point with clamps and copper wire. Stating the obvious, this should be done with the correct size copper/clamps before concrete is poured. As the structure is built clamps and copper wire are connected to the rebar completing an electrical circuit all the way to the top of the structure. This is done from each earthing point on the ground. Test points are provided along the columns to check that the system does not lose its integrity over time.

Existing buildings can have a type of Faraday's cage built to protect them from lightening strikes. Sized aluminium or copper tubing (all clamped and connected) is run along the roof peaks, parapet walls and the high extremities of a building, for example a balcony wall. For aesthetic reasons, the aluminium tubing can be hidden by plastering it one or two millimetres below the surface. Aluminium tubing is then run down the outside of the building hidden in downpipes or beneath plaster again at intervals of less than 50m. At ground level it is clamped to copper rods which have a value of less than 50 ohms to earth. Make sure that at whatever point lightening strikes, it is able to discharge directly DOWNWARDS to earth. If the discharge path to earth is first up along a conductor and then down to earth, the lightening may decide to take an alternative route and could blast a huge chunk of the building away.

I understand lightening arrestors (in this context) as lightening rods. These are usually copper and vary in design. These rods are placed on the highest point of a structure and theoretically form a type of "protective canopy" against lightening. This "canopy" is measured at an angle from the top of the copper rod down towards the ground. (I believe the angle is 60 degrees but anyone in the know, please correct me.) Any area that falls out of this umbrella region is unprotected and therefore another lightening rod would be required to expand the "protective canopy". Perhaps a good example would be lightening rods placed on the four corners of a building. These lightening rods are usually tied down to earth with the existing lightening protection system. If not they would require a low resistance path to earth, again making sure that no part of the discharge path provided is in an upward direction.

To protect the electrical supply within a building there are a number of things one can do but the first place to start is a good earth. Lightening can cause surges within a building through poor earthing practices alone. The electrical supply should be earthed at one point. The best place to earth is where power is fed into the main distribution board from the electricity supplier. Create a good earth using a copper spike in the ground with a measured value of 10 ohms or less to earth. Places like hospitals which run sensitive equipment may need a better measured value of less than 1 ohm. If lightening strikes the ground on one side of a building it causes a momentary high charge on that side of the building while on the other end there is no charge. This causes a potential difference across the building. The potential difference can cause bad surges induced into the buildings electrical circuits especially if the electrical earth is grounded on both sides of the building.

Hope that you manage to get all the correct information for your application. Good luck!

Did you get enough information to complete this project successfully sants44?

ya thank you. but i'm searching for some information regarding forming the mesh and earthing the conductors. thank you in advance.

what is cateria to instslled lighting arrestor