[TowerTalk] Fwd: Grounding connection to tower legs

[Paul Christensen]

>"I also got a question about CadWeld and those are great for ground
electrodes but I would never use them on the tower itself.  It may be
possible to safely weld a connection to a tower but I wouldn't do it to a
tubular load-bearing leg, not to mention the dissimilar metals involved and
all that."

Good advice.  Once the Cadweld shot is ignited, there's essentially no
control over flow - and the reason for keeping the molding within a ceramic
crucible.  But, lack of operator control is probably why only mechanical and
exothermic bonding is allowed under the NEC.  It's an attempt to try and
keep every shot uniform for consistent bonding, whether or not the user is
skilled in setting up the shot.

Presumably, exothermic bonding is also the only method allowed under NEC to
join dissimilar metals like steel rebar with soft copper wire.   Without
some research, I can't cite a specific NEC rule, but it is stated that way
in Whitaker's excellent book on bonding and grounding for communications
facilities:  It's titled: "AC Power Systems Handbook," 3rd ed.   Incredibly,
someone had the guts to post the complete 400+ page edition on-line complete
with Adobe indexing.  

I recently installed a Ufer ground inside two self-supporting tower piers
but did not use Cadweld shots mostly due to the hassle factor of getting
good access to the lower rebar grid plate that's down about 10 ft. under
ground level.  Instead, #2 copper wire enters 1/2-inch PVC on one side of
the pier then drops along a side wall and moves across the bottom grid in a
sweeping, serpentine fashion.  The rebar is mechanically bonded to the wire
using Harger rebar-to-copper clamps meant for the job.  There's about a
dozen rebar connection points, then the wire exists to the opposite top pier
through 1/2-inch PVC.   I had a helluva' time explaining it to the county
inspector who was initially dead-set on making me ground the pier exactly as
shown on Pirod base diagram.  That diagram simply shows each base leg
connected to an 8-ft. ground rod with a common ground rod clamp. 

Paul, W9AC