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Willie,

the currents in cloud to ground lighting strokes are measured in tens of thousands of Amps, with a very short rise-time. Although one can try to protect, as much as possible, physical structures from the effects of lighting strikes, it's very difficult to protect electrical and electronic equipment from a direct strike.

As to the codes of practice which apply in the county in which your neighbour resides, that needs digging on your part. One might start at . (An insurer may require conformance to particular standards.)

Realistically, though, if lightning strikes your house, or very close, the best you can hope for is that any lightning arrestor sacrifices itself to protect your expensive equipment. Realistically, that won't happen for radio gear with an antenna attached, whether it uses semiconductors or valves (tubes.) Likewise, TVs, other radios, Hi-Fi, computing gear, anything like that is pretty suspect after Thor has given vent to his feelings.

As an example, a while ago, I lived in a block of flats, with a communal TV system. An otherwise long-lasting robust satellite TV dongle was plugged in, and worked its magic perfectly. Until the dreadful day when, with no warning, there was a very local strike. Literally flash, bang, and the TV dongle died. Poof, it was no more. But the connected computer seemed, otherwise, to be OK. However, after about 6 months two computers, connected by Ethernet cables and a hub, both ceased to function. For one of them, it was the USB port that went first, and then the machine slowly died over a period of months.

How did that happen? Consider your neighbour's house. It probably has phone and power cables coming in, whose ground reference point is a mile or two away. And imagine that the house's ground rods' DC resistance to ground is, say, 10Ω. And say that the current from a down-stroke is 30,000A. Then there is an instantaneous potential difference between the house, considered as an equipotential Faraday cage, and local ground of 300kV. And those incoming service wires are suddenly at a potential well above what their insulation is good for. [Even with perfect ground rods of 0Ω, the resistivity of the ground itself comes in to play when tens of kilo Amps flows through it.]

If a bonding conductor in your neighbour's house had been coiled up, forming an inductor, the current from a direct hit will just jump straight across the coil to the nearest lower potential point (assuming it flowed there rather than somewhere else.) The benefit of a good thick bonding conductor, with no sudden bends, is that it tends to enforce a current path, minimising the risk that the Faraday cage becomes broken. That said, incoming services in modern houses break the Faraday cage unless there is some sort of bonding at the ingress point. But, even with bonding, the induced currents, and thus voltages, associated with a lightning strike can be vicious.

To summarise:

* it's not just the local grounding, it's the bonding of both the building structure and the incoming services (and any local cables such as antenna feeders and shed power wires) which is important;

* domestic lightning arrestors are designed to suppress secondary strikes rather than for a full, local, direct stroke;

* the principal concerns of the codes are to protect the building and its inhabitants. Protecting electrical equipment from lightning damage is both optional and specific to that particular installation;

* a Megger can tell you what the low frequency or DC resistance between two points is. For instance between the local house ground rods and the incoming power earth, or between two ground rods, or between three ground rods (which allows computing the approximate resistance to ground of an individual rod.) What it will not tell you is whether or not the internal bonding is installed according to the applicable code. Short of X-ray vision, checking bonding probably involves looking behind panels, and remote viewing kit may also be required.

Finally, none of this is professional advice. If legal action is contemplated, then such advice is probably essential to the success of any claim.

That was a very interesting question, and took me back quite a few years to when I first read some review papers on lightning and its effects.

My apologies if any of the above is teaching Grandma to suck eggs,

73, Stay Safe,

Robin, G8DQX (who lives where lightning is less prevalent, but still present)

PS: Most domestic equipment is not designed to be proof against a direct lightning strike to its enclosing building, simply because a) it's not a well-conditioned problem, and b) a domestic customer will generally not pay the extra that would be required for such robust survivability.

Somewhat OT and maybe only arguably relevant, so I started a new thread, feel free to use "Mute Topic" below.

How do you know your ground is any good?  While the primary use of grounds is for grid voltage safety, we in the RF world care about grounds for two additional reasons:

1) A place for RF to go, either as a ground plane for a vertical antenna, or a 'counterpoise' for an EFHW or long wire or something, or a 'sink' for unwanted RF in the shack.

2) A place for lightning to go, with appropriate lightning arresters on all building penetrations, including antennas and control cables, phone and cable lines, grid power, etc.

But how do you _test_ your grounding arrangement to make sure it's actually working like you think, and see if it has a low enough impedance to handle lightning strikes?

Please note:  I've been doing "best practices" for the design and implementation of grounding systems (Polyphaser lightning arresters, large ground conductors, straight runs, no sharp bends, no coils, as directly as possible from the lightning arresters to the ground rod, etc) for 3 decades or more.  I don't want to know how to _do_ grounding, I want to know how to _test_ my grounds.

I see "Ground Testers" on Amazon and other places from the $200 range to the $4K range, but now that I'm retired, I no longer have the luxury of writing off test equipment, and never having used one of them I don't know how they work, much less how well they work.

The actual issue at the moment is a neighbor's brand new house that appears to have taken a lighning strike, which blew up several thousand dollars worth of network equipment, some light controls, and maybe a clothes washer and 2/3 of his HVAC system.  The builder swears up and down the grounding was "done right", but I'm not even sure he knows what that means, and I _know_ the ground for the lightning arresters isn't right (too long, coiled up wire, goes all over before it's twisted around another green wire in a box in the basement, etc), but without tearing it all apart to inspect every junction and see if the physical wiring matches the "as built" plans (much less the architectural drawings), I'd like a piece of test equipment that can tell me "is this ground any good?".  Plus a different contractor did the network wiring and lighting arresters, so the GC is all finger-pointing and 'not my problem'.

The simplest test equipment of course is a plug-in AC line tester with 3 lights, one of which tells me if there's an open ground.  But that's not very sensitive, because it doesn't tell me how good the ground is.  Yes, the ground is functional at a milliamp or so, but doesn't tell me how it'd respond to a multi-kilo-amp lightning strike, much less stray RF from a 10W-class transmitter.  [See, now it's QRP-labs relevant!]

Does anyone know how those "Ground Tester" devices (sometimes called Megger or "Ground resistance tester") devices work, what they use for a reference, and if they tell you anything about AC or RF performance?  Is there an easy way to use a nanoVNA to check the impedance of a ground connection?

Many thanks in advance for any hints, or experiences people have had with the above!

73, Willie N1JBJ