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Old 15-10-2019, 08:20   #1
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mast step and bonding wire for lightning protection

I am in the process of tying up all chainplates (minus the insulated backstay) with a 8AWG tinned copper wire. I have a keel stepped mast, my ballast is fully enclosed(no keelbolts) so i have a dynaplate.
Idea is to run this wire to a dynaplate and connect each bronze through hull to it. Base of the mast sits on a thin insulated teflon or plastic sheet between aluminum mast and the stainless mast step. Mast step is bolted to the cross stringer.

Since mast sits on an insulated plastic (very thin sheet) it is DC insulated so no stray currents. In terms of lightning, I imagine i have enough capacitance to present a low impedance path for lightning should the surge current travel through aluminum mast in addition to shrouds. I would expect most of the surge will travel through shrouds but Stainless is not as good of conductor as aluminum so Id like to add provision for surge that might travel through the mast. My question is do i put a jumper wire from base of aluminum mast to the step where the rest of the 8AWG bonding wire is connected, or do i add caps or MOVs or a DC blocking device what will act as a lightning or RF short, between mast base and mast step.
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Old 18-10-2019, 00:49   #2
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Re: mast step and bonding wire for lightning protection

8awg wire won’t help a whole lot for a lightning strike.... copper bar about 1/2 inch square might be a good start.... even the dynaplate only really does much for a radio ground. Things like mov’s will just cease to exist in a blinding flash.....

Where you are concerned about higher risk of a strike, a heavy chain or cable wrapped around the mast and chainplates dropped into the water both sides is likely to do more to help.....

In my experience lightning tends to not behave as you would expect.... seems like it has a mind of its own, sometimes not going down the (apparently) more conducive path - I’ve seen it blow through a rubber aircraft tyre instead of going along the purpose designed earthing lead..... heard stories of it going clean through fibreglass hull sides instead of through “lightning protection systems”
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Old 18-10-2019, 07:26   #3
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Re: mast step and bonding wire for lightning protection

That does not sound very encouraging. From what i read, 8 AWG is a minimum bonding wire size. I have to assume its better than nothing. Ohm's law persists even in lightning strike, we just fail to understand how it applies beyond DC operation.
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Old 18-10-2019, 10:52   #4
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Re: mast step and bonding wire for lightning protection

Lightning starts as a mega high voltage DC charge but as it strikes it becomes a damped high frequency AC wave. You can hear the effect in a radio. It's not just a snap, but a crashing sound. The quickly diminishing AC voltage acts differently than a straight DC arc due to the capacitive effects of the materials it encounters.


To back up my statement, I found this:


https://www.nemasurge.org/wp-content.../grounding.pdf
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Old 18-10-2019, 11:40   #5
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Re: mast step and bonding wire for lightning protection

If I correctly understand what you are asking, I would tie two of the Dynaplate bolts together with some 1 x 1/4" copper bar stock, do the same on the second pair of Dynaplate bolts (if your DP is not big enough to have 4 mounting bolts, it is probably not large enough). Then drill and tap the sides of the mast a few inches from the the base of the mast and run # 1/0 or so to each copper bar stock connector. Repeat for the other set of bolt. Then tie all rigging bonding wires to the copper bars or DP bolts.

That aluminium mast is going to conduct the majority of the current from a direct hit, but bonding the rigging helps prevent flash over problems by attempting to keep everything at the same voltage level.


Dynaplate don't have a great reputation for handling lightning strikes. One issue might be people just connecting one bolt and that single connection is just not up to the task. Thus my suggestion of tying all the bolts together.

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Old 18-10-2019, 12:51   #6
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Re: mast step and bonding wire for lightning protection

Lightning protection codes were updated a few years ago.
The primary lightning downconductor should be a minimum of #4AWG, and the secondary bonding conductors #6AWG.



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Old 18-10-2019, 17:15   #7
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Re: mast step and bonding wire for lightning protection

Quote:
Originally Posted by phorvati View Post
...........
Since mast sits on an insulated plastic (very thin sheet) it is DC insulated so no stray currents. In terms of lightning, I imagine i have enough capacitance to present a low impedance path for lightning should the surge current travel through aluminum mast in addition to shrouds. .......
I very much doubt there would be anywhere near enough capacitance to be useful.

I also very much doubt the very thin sheet of plastic under the mast would have anything remotely near the dielectric strength needed to prevent the arc breaking it down.
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