I hope I'm not beating on an issue that folks have no interest in, but now that I'm installing a very expensive new electronics suite I am paranoid about a lightning strike (I live in the Chesapeake).
Inconsistencies exist in descriptions and ABYC code of how to properly wire a lightning ground. ABYC TE-4 "Lightning Protection" goes into some detail. I will paraphrase what I *think* the important points are:
1) An Air Terminal is recommended. This is simply a copper or aluminum rod that protrudes vertically from the mast and is higher than your VHF antenna. Anecdotally, driving around my very crowded marina (many hundred of boats) I haven't yet seen one boat fitted with an obvious air terminal. We get a lot of lightning here in the summer. An air terminal seems super easy to fit - thread an aluminum rod into the top plate. Maybe this would prevent VHF antennas from getting vaporized?
2) Primary conductors should be at least #4 AWG wire. For a T37, this would connect the mast step with the forward grounding bolt in the bilge for the most direct path.
3) Secondary conductors should be at least #6 wire and connect all standing rigging and the fuel tank and be routed as directly as possible to the grounding bolt (we have two in the bilge, one in back of the mast step and one approx. 7 ft aft in front of the engine).
4) Rules exist for interconnecting electrical equipment. Is this really a "drain wire"? I'm not sure. But I have drain wires on my Axiom MFD and my AIS. It seems to me these need to go to a secondary connector. TE-4 says the following:
If the case of electrical equipment is internally connected to the DC negative and the negative cable is #6 AWG or larger this cable may also serve as the secondary lightning conductor.
If the case of the electrical equipment is not internally connected to the DC negative or the connection is less than #6 AWG then a secondary lightning conductor shall be installed.It turns out that my DC negative cable is larger than #6 and goes to the grounding bus that connects to the engine. So, the way I read this is that I can connect my electrical drain wires here. Right?
5) Other large metal objects include bow and stern pulpits. Are these connected to the secondary connectors? I have no idea but maybe there's a branch that stems off from the copper wire going to the forestay and backstay. BTW, the T37 copper wire can't possibly meet the new ABYC secondary conductor standard. It seems too thin to me and also it has crazy bends all over the place.
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ABYC Grounding Schematic.jpg [ 142.16 KB | Viewed 0 times ] 6) It seems that for a T37, the lightning grounding terminal is the keel (I assume we don't have a lightning grounding plate because those bolts are bedded into the lead keel). Is this right? If so, then it seems superfluous to have a conductor connecting the two keel bolts. Stan Honey's article seems to confirm this.
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Stan Honey Grounding Figure.jpg [ 223.28 KB | Viewed 0 times ] Honey also says of the grounding system that there should be "no DC connections to the engine or the yacht's electrical system.
So, here are my thoughts on what to do from here to more adequately protect my boat:
1) Keep my lightning protection system separate from my RF drain and DC neg by removing the conductor running between the keel bolts. I will be wiring new mast lights so these will need to have their own DC return line (i.e. not be grounded to the mast).
2) Attach a proper #6G secondary conductor to the fuel tank and run it to the forward keel bolt. Remove original copper wire from the DC neg bus.
3) Connect my electronics drain wires to my DC neg bus, which is connected to the engine and the aft keel bolt as per the Honey diagram.
4) Remove the backstay conductor
5) Attach an air terminal to the mast
Perhaps I'm making this more difficult than it should be but it just seems there is a lot of conflicting and confusing information out there.