Jim,
You only think that there is no ground between your house and shack/garage.
That neutral wire is serving both as ground and neutral between the two
buildings.
What you are doing is no longer permitted by the NEC. Some 20 (?) years ago
you could run only 3 wires. And you could have no other wires running
between the two buildings.
Now 4 wires are required and a ground is required at each building with
neutral not bonded to ground at the garage. Neutral is only bonded at the
main service entrance panel.
With the old way (only 3 wires) there is going to be an AC potential
difference between the house ground and the garage ground due the voltage
drop on the neutral wire. This is why they (NEC) did not want any other
wires or conductors, including pipes etc run between the buildings as they
could carry neutral current.
By not bonding your tower to your shack ground you are risking electrical
shock if your shack ground should for some reason become elevated (fault to
ground on a piece of equipment). All you need do is be connecting or
disconnecting a coax cable that feeds the tower from your shack ground panel
and you get between the elevated ground and the tower ground.
This is why the NEC requires all grounds to be bonded with a permanent
connection. You can not depend on your coax cables for this bond connection.
Remember a connection to earth will NOT trip a breaker in most cases!
With either power feed system if there is a lightning strike on the tower or
the power line, energy is going to be fed to the other building no matter
how many ground rods you may have installed.
The NEC requires ALL ground rods, towers etc to all be bonded together.
The whole idea as far as the NEC is concerned is that they do not want any
chance of any voltage differences between grounds.
As far as lightning is concerned it is also important to have all grounds
bonded together as there is no such thing as a perfect ground so when there
is lightning energy involved you want the whole ground system to rise and
fall together as close as possible so there is never a voltage difference
across any equipment.
Lightning can come in on the power line and exit at your tower ground just
as easily as it can come in on your tower and exit at your power ground. Yes
each ground system is going to take part of the energy to ground before all
of it reaches the other grounds but some will make it there no matter what.
You just want to control the path as much as possible.
73
Gary K4FMX
> -----Original Message-----
> From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of
> Jim Brown
> Sent: Friday, September 12, 2014 5:25 PM
> To: towertalk@contesting.com
> Subject: Re: [TowerTalk] Challenging Grounding/Bonding Situation ?
>
> On Fri,9/12/2014 2:26 PM, N3AE wrote:
> > My main concern is that electric feeder to the garage. The feeder
> enters the house basement on the "north" side and runs to the main
> service panel along the unfinished basement ceiling. Don't want
> lightning currents to prefer that route. The second concern is routing
> the coax conduit near the #4 bonding wire between the tower and house
> service panel. Possible inductive coupling during a lightning event?
>
> Hi Shawn,
>
> There's a point of clarification needed here. Do you have one service,
> or two? That is, does the from the power company go first to the house
> and then to the garage (or vice versa), or do you have two feeds from
> the power company, one to each building? From your description, it
> sounds like you have the first option. Right?
>
> Here's the concern. In any SYSTEM, they must be one, AND ONLY ONE, bond
> between Neutral and the Green wire, and that bond must be where the
> system is established (usually where power enters the building). Breaker
> panels come with a bond between neutral and the frame (where the green
> wires must be connected), so if there is more than one panel in a
> system, that bond must be removed on sub-panels.
>
> There is another way to do it, and that's what I'm doing with a similar
> feed. I am treating my two buildings as separate (they're about 30 ft
> apart). I have a single service, which comes to the house, then is fed
> to the garage/apartment that houses my shack. There is NO ground
> connection between the house and the shack -- the feed from the service
> is two hots and a neutral only. In the garage/shack, this allows me to
> bond neutral at the entry panel. Note also that there are no other
> cables carrying "ground" between the two buildings.
>
> My tower is about 225 ft from the shack, so it is NOT bonded to either
> shack or house grounds. The garage/shack has about 8 driven rods --
> three on the side by the entry/breaker panel, two more around the
> perimeter, and three outside the shack. #4 runs around the perimeter,
> picks up all the rods, runs up to the antenna panel about 2 ft off
> ground. Steel conduit (EMT) brings power to multiple 120V and 240V
> outlets below the operating desk.
>
> At the house, I have three driven rods near the service entrance. There
> were none when I bought the house -- a "ground" wire ran about 35 ft to
> a spigot for a garden hose, which was fed by PVC pipe. :) Telco and CATV
> grounds are bonded at the service entrance.
>
> With respect to the tower -- coax shield should be bonded to the tower
> top and bottom. From each tower leg, at least one driven rod, preferably
> more spaced out from the tower a distance equal to at least the length
> of the rod. Also a bond from the tower to the structural mesh within the
> tower base. I do that with copper strap, using clamps for the tower legs
> that prevent dissimilar metal issues. I think I got them from DX Eng.
>
> 73, Jim K9YC
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