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MERLIN LEGEND Communications System Release 6.1
Installation
555-661-140
Issue 1
August 1998
Installing the Control Unit
Page 2-13
AC Power and Grounding
!
WARNING:
!
An improper ground can cause equipment failures, service
outages, and electrical shock. Verify that the AC power uses an
approved ground for its primary ground, that all voltage-limiting
devices are grounded to an approved ground, and that the ground
is one of the approved grounds listed below.
Approved Grounds
Approved grounds are listed below, in order of preference:
■ Building Steel. The most preferred ground.
■ Acceptable Water Pipe. Must be a metal,
not plastic or vinyl,
underground water pipe at least ½ in. (1.27 cm) in diameter, and
in direct contact with the earth for at least 10 ft. (3 m).
It must be electrically continuous so that the protector ground is
uninterrupted. (Check for insulated joints, plastic pipe, and plastic
water meters that might interrupt electrical continuity.)
A metallic underground water pipe must be supplemented by the
metal frame of the building, a concrete-encased ground, or a
ground ring. If these grounds are not available, the water pipe
ground can be supplemented by one of the following types of
grounds:
— Other local metal underground systems or structures, such
as tanks and piping systems,
but not gas pipes
— Rod and pipe electrodes, a 5/8-in. (1.58-cm) solid rod or
¼-in. (0.63-cm) conduit or pipe electrode driven to a
minimum depth of 8 ft. (244 cm)
— Plate electrode, a minimum of 2 square ft. (61 square cm)
of metallic surface exposed to the exterior soil
■ Concrete-Encased Ground. Must be an electrode, consisting of
one of the following: