[TowerTalk] tiewrapping rebar

[Steve Gehring]

N2EA is right.  

Lightning protection shouldn't just rely on the tower base's UFER ground
according to NFPA and UL industrial comm. site requirements.  In new
construction, the rebar cage in the tower's foundation should be
exothermically welded, or bonded, to the extensive grounding conductor
mentioned in the paragraph below.  Here are some paraphrased excerpts from
Harger's Lightning and Grounding Master Equipment Catalog, issued 1/02.  ***
This is by no means a definitive word or complete protection scheme, and
this only shows that there is far more involved and probably needed in the
protection of amateur tower installations. 

In terms of lightning dissipation, industrial structural protection for
towers includes the use of 5/8th inch, copper clad, 10 foot ground rods that
are exothermically bonded together using a minimum of #2 gauge solid tin
coated copper conductor.  They should form a ring around the tower, with the
addition of a combination of a conductor radial(s) extending outward, with
ground rods exothermically welded every 16 feet, to meet the required ground
resistance (based on their additional need due to soil conductivity).  All
ground rods and bonding conductors should be buried a minimum of two feet
below grade or the frost line.

The tower's legs are used as down conductors, since they provide an
acceptable path for conductance.  The ground conductor mentioned in the
paragraph above should be bonded to each leg of the tower utilizing an
exothermic or a mechanical conductor to pipe or guy wire clamp assy.   

The industrial spec goes on to say that all coaxial runs should be grounded
to the tower at the top and bottom, as well as every 75 feet if the tower
exceeds 150 ft in height.  The cables should also be grounded (preferably
with surge suppression devices) before entering the building.  

Obviously, many other grounding and bonding requirements haven't been
addressed here.  Please reference acceptable information sources and
manufacturers of grounding and bonding equipment.  

Such as:

1. Harger Lightning and Grounding
2. Joslyn
3. PolyPhaser Corporation

Good luck and happy reading! Please carefully engineer to YOUR own peace of
mind, as well as your insurance company's!

73 de Steve, KZ9G
kz9g at arrl.net


-----Original Message-----
From: towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Jarvis
Sent: Sunday, September 21, 2003 12:27 PM
To: Towertalk
Subject: [TowerTalk] tiewrapping rebar



Been following this thread with some curiosity.
Rebar is normally wire-wrapped, to hold it in place
until the concrete forms around it.

Somewhere in here, someone discussed GROUNDING the
rebar...and the term "Ufer ground" popped up.  I have
never heard the term, in 45 years, so don't know what's intended.

HOWEVER, the idea of running ground through the concrete foundation of a
tower is probably a bad one.  

Every broadcast tower I've worked with has gone to great lengths to provide
lightning dissipation grounds which route strike currents around and away
from the foundations.  

A million amperes flowing through the rebar will cause the concrete to
explode.  Then your tower comes down.  Might be amusing for a few seconds,
but the cleanup will hurt.  

If the idea is to provide a positively bonded wire cage, so there's no
incidental rectification from adjacent materials within the foundation....I
don't think I'd worry about it, unless my antenna was known to be in a high
RF field where 
rectification by subteranian metals might contribute noise
to reception on another antenna or band.  

n2ea


_______________________________________________

See: http://www.mscomputer.com  for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more.  Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.

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