By not bonding the rebar you run the risk of an arc inside the foundation
with a lightning strike. Part of the strike will go through the bolts that
the tower is bolted to in the concrete. Even if you have a good external
> -----Original Message-----
> From: firstname.lastname@example.org [mailto:towertalk-
> email@example.com] On Behalf Of Jim Jarvis
> Sent: Sunday, January 29, 2006 12:48 PM
> To: firstname.lastname@example.org; email@example.com
> Subject: [TowerTalk] tower base grounding
> Dick, (TT):
> You raise several questions:
> "The (inspector's) note said all rebar must be bonded to the ground grid,
> and inspection
> will be required prior to backfill. "
> I think an argument can be made for NOT bonding the rebar. Rather, a
> system should run OVER and OUTSIDE the foundation, and connect to your
> planned lightning
> dispersal ground system. My recommendation would be to meet with the
> inspector or planning
> officer and discuss the technical merits of each approach...find out why
> they want to route
> a strike through the foundation, rather than around it...and then go with
> what is required.
> "A bigger concern is that I was going to try to dig the 2.5' x 2.5' x 4'
> by hand in order to get a nice square hole exactly to the required
> dimensions and pour the concrete against undisturbed soil. "
> Depending on your soil, and flood factors, this is a major consideration.
> The ability of the foundation to withstand overturning moment is highly
> upon the soil density. Over-excavation and backfilling will diminish that
> substantially, unless you layer the backfill and use a power-tamper as you
> I'd vote for hand digging, so long as it's YOU and not I who are digging.
> On the other hand, a guyed tower's foundation basically supports vertical
> loads, not overturning moments...particularly true where you have a pin
> Personally, I'd excavate and tamp the refill, just to minimize the
> over the next couple of years.
> " Do building codes address non-AC cable runs? Has anyone
> out there been required to install conduit just for coax/hardline and
> low-voltage control cables?"
> As I understand it..and I am NOT a student of the NEC, the code DOES
> low voltage wiring. My recommendation would be to indicate to the code
> that you're NOT going to use conduit, that the nature of amateur
> requires flexibility with multiple low-voltage cables, and NO AC
> you're using direct-buriable hardline for RF feed, as is commonly done in
> installations, and the local cable company. If you decide to use conduit,
> it will
> only be for cosmetic reasons, to keep the cables out of sight. The 4'
> is to avoid personnel safety for folks like cable and telco, and
> who use vibratory plows to pull stuff in 18" below the surface.
> Someone with knowledge of code specifics may want to address this point,
> but I think it's finessable.
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