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Old 22-08-2010, 22:07   #1
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Question for All You Lightning Rods

OK ...We have just rewired our boat and have original wires coming off all the main chain-plates for lighting I guess.

Neither the electrician nor i remember where these were hooked to.

The back stay ones seem to line up with hooking up to the through hull radio grounding plate...I forget the brand name but it is about 4" x 10' and gold in color and very porous.

The front ones all terminate around the mast base but we have no clue as to where they should hook to....The yard suggested hooking then to my new SS mast base but that makes no sense to me. The current would just make a loop...actually it would have to jump as my mast is now insulated from the mast base with delrin.

Im thinking hooking to a keel bolt would be better.

Any thoughts?
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Old 23-08-2010, 04:46   #2
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mine hook to a keel bolt
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Old 23-08-2010, 08:32   #3
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Quote:
Originally Posted by Don Lucas View Post
mine hook to a keel bolt
Thanks Don....Thats one conformation....I was at the boat again and see the yard did indeed hook them up to the new SS mast bace...I will change it myself as that makes no sence to me...the charge would dead end not good!.
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Old 23-08-2010, 09:43   #4
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Lightning protection downconductors & bonding cables must terminate in/at the water.

Generally, this may be accomplished by connecting to a ground plate, thence an external lead keel or external grounding electrode.

See also:

ABYC Standard E-4, Lightning Protection

And ➥ http://www.iamimarine.org/iami/exchange.pdf

And ➥ http://www.inamarmarine.com/pdf/mas_...spring2001.pdf
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Old 23-08-2010, 16:58   #5
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To the keel bolts and ground plate it is then.....Pretty much what I figured....Thanks Gents


I guess this is where Im supposed to insert " I love this place' or some thing of that nature..
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Old 23-08-2010, 17:14   #6
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I think the deviation is something like 8 inches
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Old 23-08-2010, 22:07   #7
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I think the deviation is something like 8 inches
I know there has to be some pearl of wisdom in there somewhere ....but Im to thick to see it.
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Old 24-08-2010, 09:25   #8
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Wiring must not deviate from direct line of source by more than 8 inches....basically, keep your wire in line with the mast as close as possible avoiding angles that may cause the voltage to arc into another line of exit.
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Old 24-08-2010, 11:11   #9
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The path from the top of the mast to the water ground should be essentially straight.
Any unavoidable bends in the down-conductor should have a minimum radius of eight inches, and shall not form a bend of less than 90̊ .
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Old 24-08-2010, 11:47   #10
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Sounds about right, Gord, if I recall correctly. (Too tight a bend, and the current might find an easier path through something else or by arcing across the gap.)

It's hard to predict exactly what lightning will do, but the articles mentioned in post #4 offer some good general guidelines. (Dr. Thomson's article in Exchange is certainly worth a read!) As I understand it:

- You want all metal objects to be electrically connected, so that everything is held at roughly the same voltage and a dangerous voltage can't develop between adjacent components.

- You want the mast head to be at the same electrical potential (voltage) as the surrounding sea. If a voltage can be induced at the mast head, this will tend to attract lightning.

- If lightning does hit, you want it to have a clear path to the sea. If your down-conductors turn sharp corners, the lightning may prefer to arc across the cabin instead. If you ask the lightning to run horizontally inside the hull, it may prefer to just blow a hole right through the hull.

- Follow the NFPA 780 standard!
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Old 24-08-2010, 12:20   #11
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- If lightning does hit, you want it to have a clear path to the sea. If your down-conductors turn sharp corners, the lightning may prefer to arc across the cabin instead. If you ask the lightning to run horizontally inside the hull, it may prefer to just blow a hole right through the hull.
Exactly, hence although the above stated 8 inch radius and 90 degree MINIMUM (which is strange to comprehend this is better than closer to straight line out), seems to me avoiding as many curves as possible. The only place I would see that being an issue is trying to ground a shroud back to the keelbolt or grounding plate where some sort of sharp angle might be required.
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Old 25-08-2010, 01:29   #12
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Thanks for clearing that up....I don't understand the science in the MIN 90 degree bend....seems less is better, but so be it.

OK what about galvanic issues connecting all this different metal together?

I was told that it would be a major no-no...say hooking a aluminum mast to copper cable to SS keel bolt....and asking for more trouble then its worth.

It was said I would essentially create the electrolyte without the required submersion in one just due to all the dissimilar metals hooked together for this system.

What say you all?
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Old 25-08-2010, 06:41   #13
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Quote:
.I don't understand the science in the MIN 90 degree bend....seems less is better, but so be it.
Look at how the angle is measured in the drawing Gord attached. Straight is good, anything between straight and 90 degrees is tolerable, acute angles are bad. High currents might arc across an acute angle.

Quote:
OK what about galvanic issues connecting all this different metal together?
This is what your hull zincs are for. The bonding system is necessary to protect you against lightning and electrical shorts, but it does add the return paths between underwater components that allow galvanic corrosion to accelerate. Properly selected and placed hull zincs should keep the corrosion risk under control, as long as you wire-brush them regularly and replace them before they're gone.
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Old 25-08-2010, 06:58   #14
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The first article describes a faraday cage approach. I have added conductors and am converting my boat to this method.
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Old 25-08-2010, 07:02   #15
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CLARIFICATION - 90̊ MAXIMUM

Quote:
Originally Posted by Stillraining View Post
Thanks for clearing that up....I don't understand the science in the MIN 90 degree bend...
Quote:
Originally Posted by marshmat View Post
... Straight is good, anything between straight and 90 degrees is tolerable, acute angles are bad ...
From NFPA-780
Conductors shall maintain a horizontal and/or downward path to the ground and shall be free of excessive splices and sharp bends. No bend shall form an included angle of more than 90 degrees or have a radius of less than 8 inches.

The 90 degree bend is a MAXIMUM, not a minimum (fig. 7 is labelled missleadingly).
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