Onderwerp: Protecting NMEA 2000 bus against lightning strikes

In the past 4 years, we have had 5 very close-by lightning strikes. Never a direct hit, but close enough (like 50 metres or so) to induce a lot of voltage on our electrical wiring, killing some devices every time.

When analysing the failure patterns, it became obvious that one big killer is the voltage induction on the NMEA 2000 bus. In many cases we've found that the devices went offline, but were still working fine as stand-alone device. (Like VHF radio, chart plotter, etc.). This seems to indicate that the voltage surge fried the NMEA 2000 chipset in the devices, but did not do any other harm.

Alas, whilst surge protectors for the +/- supply lines can be readily found on the internet, it is much harder to find a surge protector for the NMEA 2000 bus.

Luckily, if you know that the NMEA 2000 bus is on the physical level identical to the good old CAN bus used in automotive and, more recently, in Smart Home, your search space widens. And indeed, in smart home one can find surge protectors for the CAN bus!

So, I bought a couple and started installing them. They are rather cheap, but you do need to install one in every drop line of the bus, and it is a bit tedious as they do not come with NMEA 2000 cabling. Good news is, though, these CAN bus surge protectors are indeed compatible with the NMEA 2000 bus and all devices still work as before. That is a good start!

I will refrain, though, from making the ultimate real-life test, if I can help it...

Here is a link with more details on how I went about it: trimaran-san.de/en/protecting-...f-lightning-strikes/

Greetings, Mathias

Good job!

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The can-bus protectors are nothing more then a pair of varistors, but packed into an industrial housing.

If someone has the courage to cut his nmea2000 cable and connect it again with 12volt varistors between all pairs and to ground, it is the same. But ways cheaper.

But the current way of lightning protecting systems invites big discharges into ships or objects. Big discharge currents can occure during a hit and cause inductive currents and overvoltage.

The new vision is to discharge slowly and controlled the charge above you and prevent large discharge currents.
Easy conducting trajects to ground are not done with this new theory.

You must or can restrict high discharge currents spikes with i.e. ferrites and capacitive charge collectors.

The effects are that a building up charge is controlled naturalized before a hit can occure.

Preventing is better than healing.

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Also lots of ferrite clamps in your nmea2000 cables prevents spikes with a very steep rise-time to damage your io-chips.

Also lots of ferrites in your coaxial cables and all cables from your mast can reduce lightning damage drastically.

Ferrite clamps makes life for varistors a lot easier.

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I could not agree more! I have used really a lot of ferrite clamps in my system. Everywhere I could think of and reach.. 100+ in total.

But there is a limit when it comes to applying them to NMEA cabling... These cables carry signals and in my experience, adding more than one ferrite is likely to distort the signal so much that the device after the ferrite cannot read the bus any more. For instance, my Triton display at the helm station had two ferrites, and it did not see my depth sounder any more, whilst my Triton display at the nav table still could. When I removed one ferrite clamp, it could see the depth sounder again.

So you proved the ferrite clamps do their job....

Exactly!