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[TowerTalk] Should base section contact rebar?

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Subject: [TowerTalk] Should base section contact rebar?
From: (Kimo C. Chun)
Date: Thu, 12 Jun 1997 23:31:41 -1000 (HST)

I am not an expert. I want to share what I did to also find out from the
learned many on this reflector what I could have done better, though too
late at this point. I did not know about this reflector a year ago to get
some wisdom before hand.

>I'm putting up an 80 ft tower, with Rohn 25 and 3 sets of uninsulated guys.
> I will be using a 3-band Yagi.  I'm using a 5 ft base section, and a
>poured concrete base with rebar.  I've read that the base section should
>not contact the rebar--dire consequences when lightning hits.  Other
>installation guides don't mention it.  Also, have any of you "wired" the
>rebar to the base section so as to help hold it in position during the

  There have been ample theories put forth on what happens when lightning
  makes a direct hit. I believe the "no contact rebar" crowd may say that
  unless the interface is a good electrical joint you can get high flash
  heating and potential flash steaming or the like of moisture in the
  concrete. OTOH others maintain that concrete will help dissipate the
  current and doesn't have enough moisture to worry about flash steam.
  Maybe the bottom line is if it is going to contact...make it a good one.
  Consult articles on the UFER Ground and consult with Polyphaser (NV).

  I used a cube shaped re-bar cage welded at every joint that was approx.
  3 to 4 inches below all surfaces (faces) of the foundation with a few
  running face to face in the x, y and z axes. I placed the cage on
  cement tile blocks on the bottom sitting on the gravel bed.

  As my tower used separate steel pipe anchors with large washer like
  protrusions, I built a square concrete form around the hole to provide
  the necessary above grade slab. Then I attached a section of tower to
  the anchors to provide stability and allow for leveling and true-ing of
  the tower section. I used 2 x 8 lumber bolted to the anchor/tower
  flanges and laid on edge across the slab forms and used wedges to make
  the tower section as vertical as possible - then nailed them down and
  rechecked for vertical. Suggest combinations of plumb bob, center bubble
  level, 4 to 6 foot level (and I eyed it up to the hopefully vertical
  edge of my neighbor's house -- yes, too close.)

  The anchor pipes do not touch the cage. They hang down from the 2 x 8's.
  I CADWELDed (Erico Products) large gauge wire jumpers between each anchor
  and the cage over (gentle curves) one foot below ground level and made
  similar large gauge wire stubs out 2 sides of the foundation at one ft.
  below grade to facilitate making a ground ring and field of ground rods
  approx. 20 ft. apart around my house. This is basically an UFER ground

  It gets more involved which you will find out if you read up on UFER
  and read info from Polyphaser. I've written too long as it is. There
  are issues of dissimilar metals, adequate conductor & rebar size,
  ground rod spacing and coordinating a "single point entry" to your house
  which may not be practical or possible.

>The same question extends to the guy anchors.  Is it not OK for the guy
>anchor rod to touch the rebar?  It's very tempting to wire them together
>during the pour.

  As above. Maybe run spokes of heavy wire from ring out to each anchor
  with more ground rods in between and CADWELDed to the guy anchor cage.

>Have any of you experienced concrete damage during a lightning hit (either
>at the base or guy anchor)?

  No lightning yet, thank goodness.

>I should be ready for the concrete truck in about a week.  I would
>appreciate hearing of your experiences.  Thanks in advance & 73!

  I split my pour across two truck loads (had to anyway for other reasons)
  to re-estimate how much more I needed for the second pour. Thus, I
  only had about one to two wheelbarrows full left in the second truck.
  Without other plans in place I told the driver to take it back. Total
  pour about 11 yards. Always go for a larger base. Concrete is cheaper
  than a tower coming down due to inadequate foundations.

  May I assume you have already weighed the pros and cons of non-insulated
  guys for grounding capability vs. cost vs. potential disruption of antenna
  performance (discussed previously on this forum).

>Dan Long (W4TQ)
>8035 Tokyo Pt.
>Dunnellon, FL 34433
>phone: 352-563-0934

  AS ALWAYS...I learn the hard way but I generally do learn. Let me know
 if you want any more info or opinions -and I welcome constructive criticism.

Aloha, Good Luck

Kimo Chun , KH7U

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