> 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_pageoption=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
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