Correct lightning arrester use

When using an external antenna with LMR 400 coaxial cable, what is the ideal location for the lightning arrester ? Should it be closer to the antenna or the point where the cable enters the wall ?

Hi @stevep. Complex topic but the deceptively simple answer is the suppressor should be bonded to a low impedance, single-point ground where the transmission line enters the building. “Single point” essentially meaning where all else is bonded – electrical panel, telco, CATV, equipment racks, etc.

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That was my feeling too…just wanted an expert opinion. Brilliant !!! Have a great weekend and thanks so much :slight_smile:

What would the thought be for on a yacht then?
We have seen them usually installed on the back of the router and are therefore allowing that surge through the interior cable runs of the vessel and only protecting that piece of kit.
Personally, this is how we do it because if the vessel gets a strike, the electrical surge is probably going to jump through other equipment and the cable trays which are usually pretty tightly packed.

Well, I can take a shot at this – but with the ultra-important caveat that we have zero experience dealing with watercraft. So, I can consider “principles only.” :grinning:

The objectives in grounding and bonding re (1) to keep all “electronics” at the same potential with regard to ground and (2) to shunt lightning/EMP to ground where it can be dissipated. Many people “get” the 2nd objective but not the first. One deals with the first objective primarily by bonding all equipment to a common point via low impedance connections. At the great risk of over-simplification, that means short routes, no sharp pends, and “fat” conductors with a lot of surface area (often straps, not wires/cables.)

As for your example (in so far as I understand it): For such situations, we’d create a solid bond between the rack and each and every piece of equipment in it. Then, we’d construct a bond between that rack and the single point ground. (See why we don’t like equipment encased in “plastic boxes” with no ground lugs? :neutral_face:)

What we never want to happen (this is where a lot of damage occurs): allow a strike to pass through “other” equipment on its way to ground. So, suppose we have a rack that is poorly bounded to the single point ground or perhaps not bonded at all. One of the devices takes a “strike” and that strike will seek ground. Suppose one of the other devices (makes no difference - router, switch, radio, etc) has a better, low impedance ground. The path of the discharge will likely be through the 2nd equipment. The result is often devastating.

Typically, in a fixed site situation, we’d bond transmission line near the antenna and again every 150 or so feet (+/-). (Yea, we often deal with very long runs of transmission lines.) But the arguably the most important bond is close to the single point ground which is likely near the equipment.

So, to be quite honest, I think we really know how to do this well in the world of communications towers, land mobile radio, and fixed network installations but, as I said, we have no expertise in marine applications. Therefore I’d defer to the several folks here have significant experience installing and maintaining sophisticated marine installations.


Hi @Rick-DC
That is exactly my understanding (on both points)!
Sadly, because we are doing retrofits on yachts and there are already 1-5 racks fully populated and we are only adding in 1-5U of equipment, we are unable to undertake the effort of properly grounding all the pre-existing equipment.
We have done quite a few AV refits on yachts and grounding is critical on these systems (more for the day to day operation than lightning protection).
Changing from shore power to generator (and losing the earth for the dock) can change the system massively and induce all sorts of humming sounds! Also the generators are changing frequencies as loads are brought on and off line. Makes a nightmare for equipment that runs on mains voltage and frequency, not an issue for the Peplink kit running through a PSU.

What size yachts are we talking?

30m to 100m
Generally the larger vessels are pretty well organised but the 30m-60m can be a cabling mess especially if they are 10+ years old

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@GNO-2014: That’s quite interesting. I’d love to have the opportunity to “see and touch” a marine install. :grinning: For such a retro-fit – in principle (again, a significant limitation) – we’d make certain our equipment was bonded and at common potential. And, we’d do everything we could to ensure the “other guy’s stuff” did not take a “short cut” across “our stuff” to ground.

What I did not touch-on, of course, was the benefit of good practice vis-a-vis hum and transient reduction, etc. Good practice helps to deal with that also, as you obviously know.

Your comments about the effects of changing from on-board power to shore power are quite interesting, BTW. In our world, the stuff we really care about runs on ferro-resonant UPSs. The stuff we still care about but where we can make some minor compromises runs on "other " UPSs – e.g., consumer variety where the output is something that roughly approximates a sine wave. :laughing:

Interesting discussion.


Got it. I was going to say that many smaller yachts do not have lightening protection. If they get struck, there is a good chance all electronics are wiped out. Is there a best practice on a smaller yacht for using a lightening arrester / ground on the antennas / LMR400 coming off of them?

@Rick-DC - pretty much the way we do it- protect our stuff!
We have clients that have been with us for a few years that are finally letting us rip out and rebuild their racks which is a very satisfying job! The amount of cables that are unused and damaged is surprising anything ever worked! Would share some photos but would get in trouble!

We have started to use inverter UPS’s (AC-DC-AC) which are really helping because we know that our kit is getting constant 220V 50Hz.

@mystery I would try isolate and ground the expensive equipment as @Rick-DC says above. It also depends on what material the vessel is built out of. Fibreglass, Aluminium, Wood, Steel, Carbon Fibre (or a mixture of them) all act differently!

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Yea, often the time/$$ spent to rip out and redo is very well worth it. But it’s often a “hard sell” to a customer/client. But when one is dealing with years of “crap on top of crap,” well, not much choice. :neutral_face:

I might add one minor comment: We’re really thankful Peplink built two DC power inputs into their Max line. That allows one to be used with “pure DC” – like from a battery. That really makes a lot of “goofy power problems” go away. :smile:

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@Rick-DC Also having the large voltage range is nice too! e.g. MBX 12-56V, BR1 MK2 10-30V.
We regularly power the BR1’s off 24V PSUs and have less issues that way.