Lightning Arrestors

Discussion in 'General Electronics Chat' started by m4yh3m, Jul 24, 2008.

  1. m4yh3m

    Thread Starter Senior Member

    Apr 28, 2004
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    When using lightning arrestors, does one need to be attached to both positive and negative terminals for complete safety? Is there a possibility for lighting to strike through the earth ground wire?
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    Lightning arrestors are usually a spark gap followed by a MOV (Metal Oxide Varistor).
    The spark gap shunts the brunt of the HV current. The MOV clamps the voltage to whatever it's rated for.

    Not much you can do about a direct hit by lightning; there's simply far too much power to dissipate.

    A bolt of lightning stuck a pine tree in the field behind my home. The tree was a foot in diameter at the base, and about 70' tall. It was split in half from the tip to the base, as one would split a hot dog with a knife, as well as being charred all over.

    It took a great deal of power to do that much damage in less than a second. It would've taken a very large conductor to bypass that much power to ground.
     
  3. m4yh3m

    Thread Starter Senior Member

    Apr 28, 2004
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    so...waste of money then?
     
  4. SgtWookie

    Expert

    Jul 17, 2007
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    No, not really. What are the odds of your electrical service getting a direct lightning strike? Rather small if it's underground. Much higher if it's above ground. Very high if you're on a hill, too.

    Surge protectors help a great deal if the strike isn't too close. UPS's are a really good item to have. My computer used to crash once a day between 5:30pm and 7:00pm when the power company switched around the grids. I bought a UPS, and it didn't crash for three years straight.

    The thing about MOVs is that once they've been stressed by a strike, they should be replaced. Most people don't, and they are running without protection as a result.
     
  5. m4yh3m

    Thread Starter Senior Member

    Apr 28, 2004
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    i read surge protectors are good for stations that send out power spikes and that they're not suited for strikes, where as arrestors are meant for strikes since they are gas filled
     
  6. theamber

    Active Member

    Jun 13, 2008
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    If a nearby house is struck and share the electrical line with you the weeker transients can travel to your home and create damage. A surge protection is recomended for this type of domino effect.
    For a direct hit you must provide a lower resistance path for the discharge of the lighting energy.
    If you want the best way to protect from a direct hit you need metal rods or braided copper lines around the house and 12 inches rods stiking out on the roof. The grounded rods need to penetrate the ground and be 9' long and 1/2" diameter 8' must be below ground.
     
  7. thingmaker3

    Retired Moderator

    May 16, 2005
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  8. Audiofilo

    Member

    Jul 15, 2008
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    Hi, As you can see at photos, specials RF Lightning Arrestors also are used to protect radio equipments, so it protect transmitter(receiver) in case lightning strike directly antennas or tower. Normally this arrestors are mounted indoors and fuse must be changed when striked. Is important connect the body to a good ground.

    Regards
     
  9. studiot

    AAC Fanatic!

    Nov 9, 2007
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    Since no one else has answered this part of your question I will tackle it.

    The short answer is yes. But the details are rather more complicated.

    The advice you have received so far can be summarised by a few statements.

    Most equipment, even building structures are unlikely to survive a direct hit.

    Direct hits are much less likely (frequent) than near misses so it is worth protecting against the effects of near misses.

    The protections should attempt to lead the induced discharge away from the locality of the protected structure/equipment to a very good earth.

    This can lead to problems if the protected equipment is also connected to earth for power or telecommunications grounding reasons. This is because the voltages (about a quarter of a million) and currents (20,000 to 60,000 amps) can locally raise the ground potential beyond safe limits for modern sensitive equipent. This temporary raising of the local ground is only momentary but can be enough to take out equipment.

    I have seen an installation where destroyed the motherboards of two Dell pcs and a Sony large screen television The internal power supplies were unaffected. None of the equipment was plugged into the power at the time, because of the thunderstorm, but the owner left the telecom data cables in place, which were grounded at the all three motherboards.

    So the answer is to also unplug data and aerial connections during a storm.
     
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