[TowerTalk] BASE REBAR and Lightning

[Michael Tope]

----- Original Message ----- 
From: "Jim Lux" <jimlux at earthlink.net>
To: <mecker at peoplepc.com>
Cc: <towertalk at contesting.com>
Sent: Friday, October 05, 2007 6:54 AM
Subject: Re: [TowerTalk] BASE REBAR and Lightning


> mecker at peoplepc.com wrote:
>> Read that base rebar (which must be electrically tied together)
>> should be internal min of 4 inches from edge of concrete base.
> 
> That's so the rebar doesn't protrude from the surface of the concrete, 
> providing a capillary gap (between concrete and rebar) for water to 
> infiltrate.
> 
>> 
>> Here's my question. (Im learning disabled...etc..etc.)
>> 
>> What about guys that use a piece of rohn 25 as the base, stick
>> the end in the 6 inches of gravel, and then fill up the rest
>> with concrete. There is no 4 inches of insulation with the earth
>> there, because the gravel has gaps  and moisture in it
>> which connect with the earth anyway. (a chemical fact)
> 
> Those guys aren't following standard concrete practice (avoiding things 
> sticking through the concrete/soil interface)
> 

That is the standard procedure if you put the bottom section of 
Rohn 25 in the concrete base. The idea is to plant the bottom of the 
tower legs in the gravel so that they won't fill up with water over time 
(this assumes your water table is lower than the bottom of the leg). 
Hence the conflict with the prescription to keep metal away from the 
concrete-soil interface. If you use J-bolts and a flat bottom base, this 
conflict in requirements is avoided, although if you really wanted to
I suppose you could put PVC extenders on the bottom of the tower 
legs  in former case so that the metal stayed inside the concrete 
envelope :-)

73, Mike W4EF..................................................