[TowerTalk] [Bulk] Re: Tower grounding connections and foundation

[Jim Lux]

On 8/8/15 8:02 AM, Paul Christensen wrote:
>> "Then there is the "default" - 10 ohms - maybe one ground rod and 18 gauge
> wire?  Hilarious!
>
> Not too hilarious on the day we were driving 24 ft. rods with a hammer drill
> just to get under 10-ohms in the sandy soil of North Florida.  Repeated 4
> times to get below that target.   Two 8. ft rods spaced 16 ft. and connected
> together with #2 copper gets you to maybe 50-60 ohms here.
>
> I can see why the G spec also requires 10-ft rods.   We saw an asymptotic
> effect when adding more and more 8 ft. rods.  The 24 ft rods allowed us to
> reach the goal line.  We went from about 30 ohms with many 8 ft. rods to 10
> ohms with just one 24 ft. rod.  The end result was about  5 ohms as measured
> with a clamp-on earth tester with the four 24 ft. rods placed at the shack
> EGB, each of the two tower bases, and in between each tower.
>
> That said, I do agree there's often a lot of "spec polishing" in the trades.
> For example, why is that a 3/4" PVC emergency drain pan line for my hot
> water heater was fine in 2001, but then local code increased it to 1" the
> next time it was replaced?  Then code required 1-1/4 just recently with the
> last heater change.  Just how hard is it to figure how big is a "big enough"
> line for a drain pan?  In 4-5 years, will that change to 1-1/2"?
>

Often it's some event occurs and that triggers a re-evaluation.  Maybe 
water heaters leak more catastrophically now?

I notice that back in the day, the pressure relief for the hot water 
heater was allowed to vent into the space where the heater was (often 
your garage), but now, it has to be routed to outside.  I can't imagine 
a huge upsurge in water heater overpressure events or valve failures 
leading to flooded garages triggering this..

Sometimes there's a good reason: the increased neutral size on 3phase 
systems feeding office/light industrial because of the increased use of 
switching power supplies with non-sinusoidal current waveforms, or the 
gradual change in terminology from "grounding" to "bonding", because of 
the perpetual confusion.