[TowerTalk] original source of "avoid sharp bends" in lightning

[David Robbins]

If i had to guess i would start looking at old installation instructions for lightning rod installation.  Did anyone make a do-it-yourself lightning rod kit?  maybe an old Sears catalog or farm supply mail order catalog would have a kit like that.

As far as why I would guess when lightning rod conductors ran down the outside of the buildings someone may have noticed corona or streamers from sharp bends in the wires.  Someone may have also noticed side flashovers from sharp corners to other objects, again more due to corona at the bend than inductance.  A few observations like that may have led to an admonition to avoid sharp bends in the wire.  that would have been long before the concept of inductance was thought of and would have been an easily observed phenomenon.


Apr 12, 2012 09:32:20 AM, jimlux at earthlink.net wrote:

On 4/11/12 10:33 PM, Grant Saviers wrote:
> might be as simple as:
>
> "Don't do anything that increases the inductance of the grounding wire" ?

the original source might say that, but it's not actually true. Until 
you get a full 360 loop, the inductance of a bend isn't much more than 
the inductance of the length of wire in the bend.

if you think about it, the increase in inductance in a loop is because 
the magnetic field from one part of the wire interacts with the field 
from another. Two pieces of wire at right angles don't couple very 
well, parallel pieces do. A 360 loop has coupling "across" the loop, 
but with an incomplete loop, much of the loop doesn't couple to anything 
else.


In any case, that's why I'm looking for the original source. I suspect 
that it's either:

1) how things were wired back in Ben Franklin's time, and it's carried 
on to this day because it doesn't hurt, even if it doesn't help, either. 
(the corollary, it takes more time to explain why not than to just do it)

2) A sharp bend produces a place where flashover/breakdown is more 
likely to occur.


I discovered a few weeks ago that a bunch of the grounding conductor 
guidelines in power substations (something that amateur radio folks are 
unlikely to have to worry about) were based on the behavior of bolts and 
materials commonly used at the turn of the last century. So that got me 
started..

(that, and Ward's article about 468)
_______________________________________________



_______________________________________________
TowerTalk mailing list
TowerTalk at contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk