What is the purpose of a lightning rod attached to the roofline of a building?

Question by fmrebaf@sbcglobal.net: What is the purpose of a lightning rod attached to the roofline of a building?
Ben Franklin and his devotees have been selling lightning rods for decades. Please tell me as to how a one inch stranded alluminum cable can safely conduct millions of amperes of current [in a lightning bolt] to a ground rod connected to a lightning rod fastened to the ridgeline of a standard frame dwelling?
I maintain that it cannot!
I maintain that the lightning rod is designed to
{ disperse, dispense, discharge, emanate, release, drain-off } static electrical charges to the overhead clouds, thereby equalizing the potential difference between storm clouds and the surface of the earth in a localized area. When this balance exists, there is much less chance of a discharge in both directions between earth and clouds.
If you disagree, please state your case in this matter. I’ll listen:

Best answer:

Answer by Doc8
Prevents the lightening from setting the building on fire. We ground a lot of things such as antennas. It is a common practice.

Add your own answer in the comments!

10 Responses to “What is the purpose of a lightning rod attached to the roofline of a building?”

  • Common Sense says:

    Seems that the lightning bolt does not listen to your theory….

  • Paul S says:

    They work, My friends barn took a hit and the rod was just about blown off the roof by the bolt but no fire!

  • mykidsRmylife says:

    Electricity will take the path of least resistance. That is why the lightening rods work. The path of least resistance is through the rod and wire to the ground.

  • Woodworkingmenace says:

    Actually, a lightning rod is supposed to bring the continuity of the Earth, onto the roof of the building, thus making the same polarity as the Earth, and make lightning not want to strike it.

    But, if the lightning is “bolting” to the ground, then the ground must have a polarity that is conductive to the pressure of the lightning strike and condusive to receiving the ions that are transferred from air to ground.

    So, if you have a negative resistance and a positive force, then the positive force will go to the negative resistance, and with the lightning rod going to ground, it makes the entire building the same resistance as the ground.

    It “will” convey the juice to the ground. As lightning has been known to strike all kinds of metal objects and not “melt” them, but travel along them to the Earth ground, via pole, wire or any other thing that happens to make a pathway to the Earth.

    I wish you well..

    Jesse

  • tulipshrine says:

    its so because the lightening caused on a rainy day or whenever , is charged and can cause harm to any humanbeing or your house or any other applaince of your home. so through lightening rod, that flowing charge or current passes into that rod which acts as a conductor (rod) and actually connected to earth and passes that charge to earth saving all the things.

    thankyou,have a nice time.

  • Benjamin N says:

    What you imagine as “draining off static” is precisely what lightning IS. Air is not a particularly conductive medium–so any “drainage” would actually be a sizable spark. In fact a lightning rod is meant to encourage such discharges–there is a strong electric field around the point of the rod.

    A 1″ thick piece of aluminum can support quite a bit of current for a short time without vaporizing. Plenty of electrons there to do the job.

  • doug_donaghue says:

    Maintain what you want. Bumble bees still fly, the Earth isn’t flat (and the Sun doesn’t move around it), and lightning rods work just fine.

    Doug

  • tbolling2 says:

    By your theory, lightning shouldn’t strike the house with the lightning rod because that house has been draining it’s electrical charge off into the air above it. If your theory held, then towers would never get struck.

    In reality, lightning is attracted to higher objects over lower ones and pointy objects over flat ones of the same height.

    Whether the aluminum cable can safely carry the current is immaterial. Who cares if the lightning rod gets ruined by getting hit. Who cares if the aluminum cable isn’t rated for the amperage. We are not talking about a steady load. We are talking about a load that is very transient and seldom has time to generate a bunch of heat in the conductor. Still, if the cable melts, that is much better than had the bolt struck the house and been transmitted by the plumbing, electrical wiring or people in the house.

    The voltage and amperage ranges I found for a lightning strike were 1 million to 100 million volts and 1 thousand to 300 thousand amps.

    An aluminum cable with a radius of 1 cm and a length of 20 meters has a resistance of .00333 ohms.

    The power lost due to resistance would range from:
    3330 Watts to 90000 times that or close to 300,000,000 watts.

    What do those numbers mean? Well, the aluminum cable would have very little problem dissipating the heat from the smaller strike and would never be able to avoid melting under the large strike.

    However, again, this doesn’t matter. Molten aluminum still conducts. The aluminum will be there long enough to conduct the lightning to ground and thus save damage to the structure.

  • Stewart H says:

    Yes, you are quite correct, the lightning rod is designed to reduce the electrical stress in the atmosphere around it and thereby reduce the probability of a strike.

    Various designs have a single or large number of sharp spikes on them to help. Some have slightly radioactive materials on their tips. The idea is that the radioactivity will ionize the air and help bleed off the charge.

    If you do get a strike, the charge will travel down the outside of the conductor but will generate some very high temperatures. The heating will increase at any point where there is a change of direction of the conductor. So, if you have installed the conductor so that it follows the profile of the building, where it bends around the building is where you will cause damage to the building and probably start a fire. A nice looking flexible conductor will do more harm than good.

    If you want to provide protection to a building then you need to erect a tower or mast with a lightning rod on the top and a good path straight down the mast to a good ground at the base of the mast. Arrange it so that the whole building falls underneath a line drawn from the top of the mast to the ground a 45 degrees.
    Anything that is within a 45 degree cone drawn from the top of the mast will be protected. You will see this method used for equipment shelters in remote locations.

  • Bidya Nand J says:

    lightning rod being sharp in shape is very much susceptible to let the enormous charge generated by thunder to pass to the ground.

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