Application Note

14
More ground resistance applications
Application sites
There are four other particular applications
where you can use the Fluke 1625-2 to measure
the capability of the earth ground system.
Cellular sites/microwave
and radio towers
At most locations there is a 4-legged tower with
each leg individually grounded. These grounds
are then connected with a copper cable. Next to
the tower is the Cell site building, housing all
the transmission equipment. Inside the building
there is a halo ground and a MGB, with the
halo ground connected to the MGB. The cell site
building is grounded at all 4 corners connected
to the MGB via a copper cable and the 4 corners
are also interconnected via copper wire. There is
also a connection between the building ground
ring and the tower ground ring.
Electrical substations
A substation is a subsidiary station on a trans-
mission and distribution system where voltage
is normally transformed from a high value to
low value. A typical substation will contain line
termination structures, high-voltage switchgear,
one or more power transformers, low-voltage
switchgear, surge protection, controls, and
metering.
Remote switching sites
Remote switching sites are also known as slick
sites, where digital line concentrators and other
telecommunications equipment is operating.
The remote site is typically grounded at either
end of the cabinet and then will have a series of
ground stakes around the cabinet connected by
copper wire.
Lightning protection at commercial/
industrial sites
Most lightning fault current protection systems
follow the design of having all four corners of
the building grounded and these are usually
connected via a copper cable. Depending on
the size of the building and the resistance value
that it was designed to achieve, the number of
ground rods will vary.
Recommended tests
End users are required to perform the same
three tests at each application: Stakeless
measurement, 3-pole Fall-of-Potential measure-
ment and Selective measurement.
Stakeless measurement
First, perform a Stakeless measurement on:
• The individual legs of the tower and
the four corners of the building
(cell sites/towers)
• All grounding connections
(electrical substations)
• The lines running to the remote site
(remote switching)
• The ground stakes of the building
(lightning protection)
A typical setup at a cellular tower installation.