Metalic apparatus to receive the discharge of a lightning near houses

DaTario · May 15, 2009

Hi All,

I would like to know what is the main reason to build those metalic apparatus to receive the discharge of a lightning near houses. I am concerned with its shape and its physical explanation.

Any help will be welcome,

Thank you all

Best wishes

DaTario

mgb_phys · May 15, 2009

Re: lightning

They are called lightning conductor and are to protect the building if it is struck by lightning.
They are simply metal wires going from above the building to ground. The idea is that the lightning hits the point rather than the building and the electrical current flows through the metal wire harmlessly to the ground instead of through the building.
Because the building has a high electrical resistance the lightning current flowing through it would produce a lot of heat energy and almost certainly start a fire.

captn · May 16, 2009

Re: lightning

mgb_phys said: ↑

They are simply metal wires going from above the building to ground. The idea is that the lightning hits the point rather than the building and the electrical current flows through the metal wire harmlessly to the ground instead of through the building.

I'm not sure if the wire would survive a direct hit.

The pointed rods (connected to ground) release a stream of electrons into the air--trying to keep the atmosphere around the building from building up a charge that would 'attract' the lightning.

If course, I don't know why the lightning doesn't see the points as 'ground' (which would be many meters above the real ground) and strike it anyway.

Neil

DaTario · May 16, 2009

Re: lightning

Hi,

You two gave the taste of my problem. There are two main reasonings and each one of you has defended one of them.

The first is that the apparatus serve as a preferential and safer conductor channel for the electricity.

The second says that the sharp edge of this apparatus serve as a leaking mechanism, which is always throwing earth-charge into the air (atmosphere). This "may" lower the earth-charge density in the neigborhood of the building, lowering therefore the probability of hapening a discharge (lightning) in the very building (or its point-apparatus).

I again welcome contributions.

Thank you

DaTario

mgb_phys · May 16, 2009

Re: lightning

The theory that lightning conductors prevent strikes by discharging the building is discredited, in fact lightning conductors may slightly increase the chance of a strike because they allow the induced ground charge to create a potential at a higher point - nearer the cloud.

DaTario · May 16, 2009

Re: lightning

Hi mgb,

Is there any reference to this point of view? Any site?

Do you believe that these two factor act together, yielding what you called "slightly increase" ?

Best wishes

DaTario

captn · May 16, 2009

Re: lightning

mgb_phys said: ↑

...may slightly increase the chance of a strike because they allow the induced ground charge to create a potential at a higher point - nearer the cloud.

This is the thought that made me add the ending statement to my post.

Neil