Protecting NMEA 2000 bus against lightning strikes

[MathiasW]

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: https://trimaran-san.de/en/protectin...tning-strikes/

Cheers, Mathias

[SoonerSailor]

I have also found that the NMEA2000 interface is particularly sensitive to lightning, leaving our AP computer, chart plotter, depth sounder, engine monitor, etc deaf and mute on the network.

[markcouz]

Would it not be possible to use LAN (RJ45) surge protection which is widely available?

[hjohnson]

Originally Posted by markcouz

Would it not be possible to use LAN (RJ45) surge protection which is widely available?

N2K, by design, carries both data and power. That might cause some issues with your typical LAN surge suppression equipment (I suppose unless it was one designed for Power over Ethernet). Even on devices that are externally powered (Autopilots, chartplotters, AIS transponders, etc...) the 12v power on the N2K seems to be used to power the actual transceiver in the system, and the N2K bus goes down if there's no power on it.

[MathiasW]

Originally Posted by markcouz

Would it not be possible to use LAN (RJ45) surge protection which is widely available?

If you look at the electrical drawing for the CAN-UES2 surge protector, you'll find that it is a design dedicated to the CAN / NMEA 2000 bus. The two gas dischargers are between the two data lines and supply/ground, respectively, and the ferrite is between the two data lines.

I do not think a generic LAN surge protection would be as specific and thus I reckon would be less effective.

[capn_billl]

I just lost all nmea 2000 devices on my boat as well.

The wind instrument and depth finder are the two that blow the most often. Probably because they are the path from mast top to water.

[MathiasW]

Originally Posted by capn_billl

I just lost all nmea 2000 devices on my boat as well.

The wind instrument and depth finder are the two that blow the most often. Probably because they are the path from mast top to water.

Sorry to hear that!

It may be worth to check whether ALL are really dead, or whether there are one or more culprits which are not only dead, but are messing up the NMEA bus so that no other device can use the bus. Happens quite regularly to me. To find them, you need to disconnect all devices from the bus, except for, e.g., two displays such as Triton on B&G. When you go into network and search for devices, and you can see the other device, you know it works. Then slowly add devices one by one and keep checking whether the network still works - i.e., whether you can still see all the devices you expect to see.

Culprits will show up as devices that when added make all other devices invisible on the bus again. Leave those disconnected and see how far you get.