[R-390] Grounds

[Bruce Ussery]

For a while I got back into the RF world as my daily job, working for the NC 
State Highway Patrol's VIPER microwave network group. (VIPER = Voice 
Interoperability Plan for Emergency Responders.) This lets anyone with the 
proper radio reach anyone else in his group statewide, when in range of any 
of around 200 towers. The new sites we installed went into nice pre-fab 
buildings with pretty impressive grounding systems. Lots of wide copper 
strips where the feedlines enter the building, lots of Polyphaser devices, 
surge protector boxes on the AC mains and generator circuits- all done 
pretty much like Dave described for larger buildings.
Even with all this effort lightening still causes damage routinely, mostly 
to the "mux shelf", a box full of circuit boards that basically sorts out 
all the signals going into, or coming out of the microwave; the generator 
controls, and the UPS box. The Alcatel microwave and Motorola trunking 
radios generally survived. Experience helps I imagine.
Thanks to all for the good information.

Bruce
WA4ZLK

----- Original Message ----- 
From: "Dave Maples" <dsmaples at comcast.net>
To: "rbethman" <rbethman at comcast.net>; <R-390 at mailman.qth.net>
Sent: Sunday, August 02, 2009 3:56 PM
Subject: Re: [R-390] Grounds


All: The NEC is correct in this case.  All the grounds need to be connected
together with large-gauge wire, so that any surge current (whether direct or
induced) cannot set up a large potential difference between the ground
systems.

In the commercial world we bond power and telco grounds together, and then
bond that to a ground ring around the building.  The ground ring around the
building is bonded to a ground ring around the tower (if any), and the tower
legs are bonded to the tower ground ring.  Three ground rods at the tower,
one ground rod at each corner of the building and more if the corners are
more than 15' apart, and all bonded to the appropriate ring.  Each coaxial
cable shield conductor is bonded to the ground ring around the building at
the point of entry into the building, and lightning protection is bonded to
the ground ring around the building.  Each telco and power entry or exit has
a suitable surge protector on it.  Inside the building, equipment grounds
are bonded to the bonding point for the power, telco, and coax shield
grounds.

This is a large condensation of guidance we received from both Polyphaser
and equipment vendors.

Hope this helps.

Dave WB4FUR
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