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Old 21-02-2010, 00:23   #1
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Built-in Lightning Protection for Electronics

Is there any merit in pursuing built-in protection for electronics?
From time to time I have come across sailors who place their smaller electronic items in the oven/microwave to secure them from imminent lightning strikes. Is their any science (other than bad science) in enclosing all the electronics at say the nav station in an insulated metal cabinet and making provision for quick disconnect or surge-protection of all aerials and external wiring? Could conceivably do same for internal or even external helms too. Would usually be done most easily at early fit-out which is reason for my asking now.
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Old 21-02-2010, 03:06   #2
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if it was lightning strikes your concerned about i wouldnt be using anything metal as steel is a great conductor as for electrical items i would simply just disconnect them from the plugs and that includes all aerials
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Old 21-02-2010, 05:39   #3
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Actually (aside from the risk of forgetting their location and turning on the oven), putting electronics inside a metal oven for lightening protection may be a good idea. This is based on the Faraday cage. The principal behind the cage is that an electric charge will stay on the outside of a hollow metal container, leaving the inside protected.
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Old 22-02-2010, 07:07   #4
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Faraday cage

So is a Faraday cage with internal insulation more effective do you think? Perhaps would need relatively little insulation compared with that required to block normal flow of lightning current?
I can see it would be easy to incorporate surge-protection into the power supply. Do not know enough about aerials.
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Old 22-02-2010, 10:43   #5
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While we're at it, disconnecting antennas, etc., what about the transducers underwater? Aren't they also subject to massive voltage surges if lightning strikes nearby? And what about the alternator, diodes, regulator etc., which share grounds?
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Old 22-02-2010, 11:08   #6
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Stillbuilding,

Some government research done a few years ago studied the resistance of various communication devices to EMP (electromagnetic pulse). Although it was aimed at rf energy generated by nuclear events, the info is applicable to to energy generated during thunderstorm/lightning events. The gear included off-the-shelf ham hf transceivers and vhf handhelds.

Tests showed that the gear was amazingly resistant to damage when power leads, control leads and antennas were disconnected (per sailfish) from the HF transceivers. Removal of the wires prevented them from behaving as antennas that fed rf into the gear. VHF handhelds were found to be resistant even with the antennas installed; VHF frequencies are less vulnerable to the greater EMP energy generated at LF, MF & HF frequencies. Nevertheless, removing them wouldn't be a bad thing.

I recall the same study also evaluated protection with Faraday cages, and found that simple grounded "wire mesh" enclosures were effective; a grounded oven might protect similarly.

Your idea for a purpose-built cabinet might be practical, coupled with a single-point grounding system, surge protection on the dc/ac wiring, antenna leads, and perhaps protection devices on specific components.

Even with correctly installed lightning/ground systems (which are aimed at protecting people), protection of sensitive solid-state components can't be guaranteed.

Good luck and let us know how your project develops.

Roger
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Old 22-02-2010, 14:09   #7
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Would not matter whether the metal shield is on the inside or outside of the structure that makes the Faraday cage (in terms of this discussion, the oven). Not sure what effect on the protection if the outside of the cage was totally covered with some form of insulation but as long as there is a complete surround of metal then the charges on the outside essentially balance out to zero on the inside. For best protection the cage should also be grounded to earth.

Does not have to be solid metal, even a wire mesh or similar would work as long as it goes completely around and is electrically connected.

You do realize of course that if there is a direct lightening strike on the stove all bets are off.
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Old 22-02-2010, 14:58   #8
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While I find the microwave or oven option interesting, to the original question - Is there any merit in pursuing built-in protection for electronics? Yes.
The real question is how far?

The best protected electronics are disconnected and put away from exposure during storms. Hard to imagine I would pull the Radar, depth finder, and GPS when a storm blew in.

Presuming we are anchored where we don't need them, I took the same route I did with my house. I am currently adding surge protection, and quick disconnects to make disconnecting at port easier. Even so, a direct hit, that is not given a better path of least resistance, is going to jump just about any surge protector. Consider a lightening bolt generates up to 100 million volts, and on average run 5000-20000 amps with recorded highs as much as 200,000 amps. Any wire in your boat capable of that type of load?

As long as the current has a better path, it is going to leave mobile electronics alone. Even if Murphy finds them? You are probably going to be in bigger trouble than the device. Here is an example where a person
NWS Lightning Survivor Stories was hit by lightning on the shore, from a storm estimated to be 2 miles out to sea.

Would a Faraday cage help protect them? It may help. You on the other hand...
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Old 23-02-2010, 01:42   #9
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Some interesting thoughts

Might still give the electronics Faraday cage a bit more thought - not difficult or hard to implement. I suppose one way of looking at a yacht is a sort of large Faraday cage - this would be the rationale of lightning protection devices! Maybe we should have more rigging aloft as improved defence. Just not touch it!

Does anyone know if it is practicable to insert lighting protection into radio aerials. I seem to recall a thread with this discussed but cannot find it.
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