Re TIA-222-G:
I would like to be enlightened why #00 wire is needed to attach to two
ground rods which are likely several ohms resistance to the "remote
earth"? Especially when #6 was ok in the last rev of the standard and
when from an I^2*R and fusing current it would do the job.
Further, it is a bit of a mystery why Ufer grounding is not included
when it is the NEC & military standard for structures containing
munitions, explosives, etc. This forum has opined extensively about why
Ufer's beat ground rods.
Is there any science and engineering behind the new rev G requirements
and documented failures of towers installed to the old standard?
Or is this "standards polishing" by parties with a beneficial interest?
I've been there, seen it happen.
Then there is the "default" - 10 ohms - maybe one ground rod and 18
gauge wire? Hilarious!
Grant KZ1W
On 8/7/2015 16:10 PM, JVarney wrote:
Patrick Greenlee wrote: >>So would circling the Ufers be redundant?<<
=====
I won't give you advice on what to do but I will share with you what the
TIA-222-G code says about grounding. Generally TIA-222-G is the governing
code, not NEC.*
Per TIA-222-G, "Protective Grounding": The default configuration for a
self-supporting tower is a star ground consisting of 6 ground rods arranged
symmetrically around the tower base with each rod separated a minimum of 20
feet apart from its neighbor, with at least one #00 wire connecting each
tower leg, each to two of the rods. If the default grounding system is not
installed then the tower owner has the option to install an alternate
system that provides no more than 10 ohms resistance to "remote earth."
Ufer grounds are not recognized by TIA-222-G; they seem to imply the
opposite because the purpose of the grounding system is to "limit damage to
the structure or foundation."
The TIA-222-G grounding requirements is a tough standard to amateurs to
meet, it's expensive and big! I think it's clear the TIA committee's
philosophy is to provide multiple low resistance paths throughout a large
volume of earth away from the tower as a way of dissipating lightning and
static charges. If I was putting in a large tower with an Ufer, I would
supplement the Ufer and mimic the TIA-222 design as best I could with big
conductors connected to each leg and multiple ground rods well away from
the tower.
73 Jim K6OK
* If the tower is immediately adjacent to a house then NEC and TIA codes
conflict with each other. Assuming the tower is well away from any
structure, TIA would apply.
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