[TowerTalk] Ufer Grounding

[David Gilbert]

Normal rebar is made from random composition steel melted down from old 
car chassis, bed springs, washing machine frames, older reclaimed rebar, 
etc.  Welds made to it have completely indeterminate strength.

Weldable rebar has controlled content and is spec'd where the rebar 
joints need to be structurally strong.  I think rebar cages for bridge 
pylons and large building columns might be an example.

I don't see any problem cadwelding copper wire to normal rebar since we 
aren't looking for structural strength anyway.  The materials (copper 
and iron/steel) are inherently different in the first place.

Dave   AB7E


On 7/15/2016 9:03 AM, Paul Christensen wrote:
>> "I thought that one is NOT supposed to ever weld to the rebar, unless the
> rebar is spec'd for welding, which most are not"
>
> No idea, but Erico sells many forms of Cadweld shots that are designed to
> bond coper wire with rebar.  Anyone know the answer?  Is there a special
> form of rebar that can only be used with an exothermic weld?
>
> Paul, W9AC
>
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces at contesting.com] On Behalf Of Dick
> Blumenstein
> Sent: Friday, July 15, 2016 11:59 AM
> To: towertalk at contesting.com
> Subject: Re: [TowerTalk] Ufer Grounding
>
> Hi Paul-
>
> I thought that one is NOT supposed to ever weld to the rebar, unless the
> rebar is spec'd for welding, which most are not; that all grounding wire
> should be clamped to the rebar and then when the wire leaves the area of the
> tower base, you should/could cad weld it to the ground rod system.
> Am I wrong here? (I'm about to build a concrete tower base with a 5' x 5' x
> 8' deep hole and a lot of rebar).
>
> Dick, K0CAT
>
> ============================
>
>
> Paul Christensen wrote on 7/14/2016 10:48 PM:
>> It's looking more probable that the remote Internet site built last
>> year by N4CC and myself will require a complete move about a half-mile
>> down the road.  Assuming this is the case, I want to pay particular
>> attention this time to Ufer grounding of the two tower bases.  These
>> are large Pirod self-supporting towers with substantial concrete
>> piers.  The relevant portion of Motorola's R56 standard is copied and
>> pasted below.  The soil in this area is very sandy and at the current
>> site, we ended up having to drive down a total of four 24 ft. rods to get
> adequately low earthing resistance.
>> That was a rough day of work even with a hammer drill.
>>
>> My thought is to "spiral wind" solid #2 AWG wire, beginning the bottom
>> rebar layer.  Cadweld it at the start point, and then periodically
>> Cadweld at random points where the wire crosses other rebar sections.
>> The wire would exit at the top of the pier using a small-diameter PVC
>> pipe as shown in one of the R56 diagrams.  As the wire nears the top,
>> possibly it could branch out into two additional directions for
>> bonding to the tower base and perimeter ring.
>>
>> Any issues with this plan?
>>
>> Paul, W9AC
>>
>> Motorola R56 Ufer Guidelines:
>>
>> . Concrete-encased electrodes shall be encased by at least 51 mm (2
>> in.) of concrete, located within and near the bottom of a concrete
>> foundation or footing that is in direct contact with the earth.
>>
>> . Concrete-encased electrodes shall be at least 6.1 m (20 ft.) of bare
>> copper conductor not smaller than 25 mm2 csa (#4 AWG) or at least 6.1
>> m (20 ft.) of one or more bare or zinc galvanized or other conductive
>> coated steel reinforcing bars or rods at least 12.7 mm (0.5 in.) in
>> diameter.
>>
>> . Concrete-encased electrodes shall be bonded to any other grounding
>> electrode system at the site.
>> See "Common Grounding (Earthing)" on page 4-5.
>>
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