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Old 28-02-2012, 16:40   #31
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Re: Lighting Protection - From Mast or From Butt Plate ?

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Originally Posted by rebel heart View Post
Can someone explain to me how a 4 gauge wire is supposed to transfer 30,000 amps?
Time and mass!

Thermodynamics are a set of much slower physical processes then electrical conduction. Thus, if the electrical conductor has sufficient mass and the electrical current stops flowing soon enough to allow it to start cooling before its temperature can rise to the melting point, it will survive.

A good example is the common fuse. This is a device that is designed to fail when excess current passes through it. Yet it will survive short bursts of current above it rated value.

Another example is the incandescent lamp. A device designed to balance the thermodynamics and current flow to be very hot and not melt. And, when you switch off the current flow to the lamp, you can watch the much slower thermodynamics in action as its element slowly dims.

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Old 28-02-2012, 16:45   #32
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Right random strikes can provide a a longer constant and these strikes are the ones that cause most fires. It all seems pretty my much up to the storm and circumstance. Having a good ground is a good start.
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Old 28-02-2012, 17:49   #33
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Re: Lighting Protection - From Mast or From Butt Plate ?

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Can someone explain to me how a 4 gauge wire is supposed to transfer 30,000 amps?
That is why 0 guage or better is a better lightening ground. Have you seen a ground wire after a strike? I have it was smoking red hot for many seconds after the strike, (I didn't time it, I was too busy ducking and listening to the ringing of my ears). Larger guage will conduct for more seconds before melting.
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Old 28-02-2012, 17:55   #34
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Re: Lighting Protection - From Mast or From Butt Plate ?

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Can someone explain to me how a 4 gauge wire is supposed to transfer 30,000 amps?
rebelheart,
Read your Ins policy carefully. When I called my ins co lady handling call said no one had ever asked her why #4 wire spec'd but upon reading my policy the underwriter had spec'd 00 gauge not #4 for the taller mast (136') and 0 gauge for the shorter mast (10' less). Left msg for underwriter to call me back or email mail where he got his specs from which he did after prolonged period and here is part of my prev post #87 from alum mast, multihills forum. (my boat then PO's got hit by lightning last year and it blew a hole out thru the alum mast 102' up. IMHO caused by poor install on lightning portection system)

"Stillbuilding,
Been busy on charter so offline couple days but Ins Co Underwriter finally got back to me. His response was they look at many such as ABYC TE-4 and NEC and then they take the toughest one currently NFPA 780-2011 Elec Fire Code and they increase the wire size to reduce their risk and my rate.

How can I argue with that?? "

FYI,

John
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Old 28-02-2012, 18:00   #35
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Re: Lighting Protection - From Mast or From Butt Plate ?

I like the fuse analogy! a 4 ga wire at the bottom of a mast will probably be alot like a fuse! I guess all this stuff just depends on the size of the strike. A search on Google turned up some huge looking bolts of lightening! My Passport 47 was struck (ungrounded) but the only thing that happened was it destroyed the windex at the top of the mast and there were carbon trails on the side of the mast at th e tangs that the uppers attach to...
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