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Roger Hayter · August 23rd 16, 02:47 PM posted to rec.radio.amateur.antenna

rickman wrote:

On 8/22/2016 7:05 AM, wrote:
On Saturday, 20 August 2016 21:32:06 UTC+1, rickman wrote:
In studying for the Technician exam I am finding questions which seem to
be making a big deal of having sharp, right angle bends in the ground
wires for lightning protection. I know that for digital electronics the
old warning about right angle bends has been shown to be pointless up to
many GHz. What is the deal with lightning? What happens when the
ground wire is bent in a right angle? Has this been verified by
experiment anywhere or by application failures?

--

Rick C

From the dim dark recesses of my memory, I think it's to do with the
passage of a very large current (1000's of amperes?)with a fast rising
edge and the intrinsic inductance of the conductor [enhanced by an
sharp/r.a. bend] as in e= ?L di/dt. Now you go research it !

Research what? I've never found anything remotely analytical or even
from experience that talks about sharp corners other than in PCB routes
where the avoidance of sharp corners has been shown to be pointless for
anything short of high GHz signals. High currents don't change the laws
of physics. Inductive reactance is about frequency. If sharp bends in
PCB traces don't have a noticeable impact on sub-GHz signals, will sharp
bends have an impact on lightning?

This seems to be a rule of thumb thing. Lots of people advise to not
have "sharp" bends or "90°" bends. Few define what that means. Some
say 8 inch radius, some say 6 inch radius, another says 1 inch radius.
I also see recommendations for the size of grounding wire all over the
map. One says #2 wire, another #4 wire, another #6 wire and another
refers to NEC which he claims says #6 is fine.

I like to do things "right", but I like to know what rules of thumb are
based on.

Electric field intensity is increased at sharp points, and can cause
arciing which would not otherwise occur. Could this be the problem the
advice is aimed at? I have no idea if a right angle bend in a thin
conductor has that much effect on field intensity, but it is amenable to
maths I think.

--

Roger Hayter