> If you are planning to use a Ufer ground, the rebar MUST be welded.
That may be the case for your local building/electrical code, or perhaps
what your inspector *thinks* is required, but it's not required by our
local code. That's because it's not required by the National Electrical
Code (NEC), on which most local electrical codes are based. Section
250.52(A), "Electrodes Permitted for Grounding", states:
(3) Concrete-Encased Electrode. An electrode encased by at least 50mm (2
in.) of concrete, located within and near the bottom of a concrete
foundation or footing that is in direct contact with the earth,
consisting of at least 6.0 m (20 ft) of one or more bare or zinc
galvanized or other electrically conductive coated steel reinforcing bar
or rods of not less than 13mm (1/2) in diameter, or consisting of at
least 6.0 m (20 ft) of bare copper conductor not smaller than 4 AWG.
Reinforcing bar shall be permitted to be bonded together by the usual
steel wire ties or other effective means.
As I recall, the well-regarded Polyphaser treatise on grounding also
states that wire ties are acceptable for bonding the rebar in a tower
Ufer ground. If you Google the subject, you'll find studies that prove
rebar connected with wire ties is adequately conductive for the purpose
of creating an effective Ufer ground.
My own tests showed zero ohms through my rebar cage, which was
constructed with wire ties. The ground system, consisting of three 50'
1/0 radials Cadwelded to 12 ground rods was connected to the cage with
pipe clamps. I measured zero ohms through the rebar cage from one radial
to each of the others, both before and after the pour. As long as the
rebar isn't touching the soil, I don't believe any deterioration of the
joints is possible after the concrete cures.
The inspector had no problem with my construction, though I was prepared
with copies of the NEC and the published studies in case he thought the
rebar needed to be welded.
Note that while the NEC states that a concrete encased rebar cage is
acceptable for use as a ground electrode, and there are published
studies indicating that concrete does conduct, the literature on Ufer
grounds is unanimous that the rebar cage must be connected to an
adequate tower ground system like the one described above.
73, Dick WC1M
-----Original Message-----
From: Dr M J DiGirolamo [mailto:DrD@2020.com]
Sent: Thursday, July 26, 2007 6:23 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rebar Cage Question
Phil,
If you are planning to use a Ufer ground, the rebar MUST be welded.
There
is a different type of rebar that you must order. Speak to the rebar
supplier (metal supplier) and they'll tell you what the number is. I
just
did one last year for a USTower 72' self standing tower. It's a totally
different beast from regular rebar - the steel is much more refined.
Surprisingly, it wasn't but a tiny bit more expensive than regular
rebar.
Be SURE ALL JOINTS are WELDED or the inspector will getcha!
You can view photos of the rebar cage (as well as my entire project)
here:
http://new.photos.yahoo.com/drd_007/album/576460762311711301?pm_pageopti
on=A
LL
73,
Mike DiGirolamo, W4XN
Charlottesville, VA
-----------------------
Message: 7
Date: Thu, 26 Jul 2007 14:32:59 -0500
From: "Larry Burke" <wi5a@sbcglobal.net>
Subject: Re: [TowerTalk] Rebar Cage Question
To: <n9lah@comcast.net>, <towertalk@contesting.com>
Message-ID: <20070726193339.66BAB31A24E@dayton.contesting.com>
Content-Type: text/plain; charset="US-ASCII"
Phil...
Welding on rebar is not the preferred method of construction, as it may
weaken the steel. Before I knew better, I tried this once and the welds
didn't hold well (and they were -- in theory anyway -- done by a
professional). Not saying it can't be done, but there are many who argue
against welding.
- Larry
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of n9lah@comcast.net
Sent: Thursday, July 26, 2007 2:06 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Rebar Cage Question
OK now we are getting to the question I have been wanting to ask. Can a
rebar cage work just as well if it is cut and welded together rather
than
bent and wire tied? It is my plan but thought I might toss the idea out
for
the critics.
Phil
N9LAH
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|