[TowerTalk] Connecting Tower to Ground Rod

[Jim Lux]

On 10/10/13 5:09 AM, Pete Smith N4ZR wrote:
> Does this standard apply even if, as in my case, the tower is 190 feet
> from the house entrance?

No. There is no requirement (in the NEC) for the antenna support 
structure grounding be bonded to the building's grounding system, if 
they are sufficiently far apart.  (810-21, notes in NEC handbook).

In the same way that your house's grounding system does not need to be 
bonded to the grounding system as the telephone company switch building. 
How far is sufficiently far?  Probably somewhere in ARt 250 it says. 
I'd guess 50 or 100 feet.




  Does it need to be a direct, dedicated
> connection, or could a hardline shield, for example, be used for the
> tower to house electrical service ground connection.  In cross section,
> even LDF4-50A is a lot beefier than #6.

The whole thing on whether coax shield can serve as the bonding 
conductor (code wise) is a bit hazy in my mind.  Is it like metallic 
raceway (which can serve as a bonding conductor)?  Or not?  In the 
"antenna lead in wire" case, the shield can serve as that conductor. 
But could it serve on a hardline run for a 20 foot run in a trench or 
cable tray?

(you don't need a bonding conductor for a 200 foot underground run, as 
discussed above)


One thing about coax is that it has connectors, and in general, bonding 
conductors have to be permanently connected.  Sure, from a functional 
standpoint, the requirement that the shield be connected to the ground 
system outside the structure is met by a bulkhead connector in a 
conductive plate.  BUT, you'll note that there are a lot of suppliers of 
kits to remove the outer insulation, and bond directly to the shield 
with bolts (wrapping some sort of clamp around the coax shield).  I 
suspect that is because a significant number of inspectors don't buy the 
"bulkhead connector as bonding" argument.

I will also say that a lot of inspectors will not be interested in 
listening to equivalent cross sectional area arguments.  They'll say, go 
get the AWG 6 (or 10 or 17 or whatever) and put it in: you're spending 
more money standing here arguing about it than you'd spend to just buy 
the wire.

I've had questions raised about *waveguide* runs and whether they needed 
a separate grounding wire.