On 5/11/2010 7:40 PM, Jim Brown wrote:
> On Tue, 11 May 2010 16:06:36 -0700 (PDT), AI4WM Bill wrote:
>
>
>> Most residential grounding is for safety and not lightning protection.
>>
> WRONG! One of the objectives of the grounding requirements of electrical
> building codes is LIGHTING SAFETY. The other objectives are fire safety and
> protection of personnel from electrical shock.
>
Sorry about double posts/e-mails. Thunderbird has changed their layout
and even though they are plainly labeled the buttons are in different
locations. And they dumped the ability to show "full headers" which
makes getting the IPs of spammers difficult.
First, our electrical inspector told me, after I remarked about the size
(or lack thereof) of the required ground after we put the drop to the
house underground, that the grounds were primarily for protection from
shock and fire. Any lightning protection was incidental.
After I look at a good ground system compared to a typical home
grounding I have to think of these points.
NO practical and economically palatable ground system is 100% protection
from a direct lightning strike.
NO ground system I've seen is 100% effective against all lightning
strikes including the "super strikes"
The ground required by code is minimal even for nearby strikes.
To gain substantial protection all lines coming into the home need to
enter at, and be grounded at a common point. This is more important to
a point that having a substantial ground system.
code for Entrance grounds apparently does not take a typical ham station
in the home into consideration.
I believe there is a section in the NEC for ham stations, antennas, and
grounding, but I've never seen it applied nor found an inspector who
appeared to be interested.
There objective may be lightning safety, but I've never seen a typical
home including current, new construction that I considered to be
properly protected from lightning by the grounds required by code.
My shop which is recent construction, has only two 8', flimsy, copper
coated, steel ground rods about 6 or 8' apart that connect to the system
ground through about 8' of #4 to meet the code. The shop has a 200A
service with it's own underground feed from the power line.
However with the antennas on the West and North side of the shop as well
as the roughly 45' run to the big tower from the South side of the shop,
the tower grounds form a bare #2 run that would completely enclose the
shop except for the concrete apron. There are 8, 8' ground rods on that
line which is also tied into the ground system for the big tower which
has over 600' of bare #2 cadwelded to 32 or 33 8' ground rods. The
house entrance gained the second ground rod when we/I put the drop
underground and installed a 200A service.
Prior to installing the elaborate ground system (and big tower) we had
several nearby strikes that did more or less minor damage. Since the
tower and ground system, the tower has been hit at least 17 times (that
have been visually verified) with no detected damage. Typically either
the 2" mast that tops out at roughly 131', or the 144/440 arrays on the
14' 1 1/2" cross boom have taken the hits. OTOH a number of neighbors
have had substantial damage in the last few years.
All the antennas up there (at the top of the 45G) are currently
disconnected for maintenance. We took the tribander down a couple weeks
ago and there was no lightning damage. We still need to get the 7L C3i
6-meter Yagi down to replace the broken boom truss, remove the cross
boom with the 144 and 440 arrays, inspect them, and replace the old
structural steel mast with 2" OD DOM, or Chrome molly tube. The 144 and
440 arrays are not going back up "on top"
73
Roger (K8RI)
> 73,
>
> Jim Brown K9YC
>
>
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