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Installing the Control Unit
WARNING:
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
The following is a list of approved grounds, starting with the most preferred:
■ building steel
■ acceptable water pipe—must be a metal, underground water pipe at
least ½-inch (30.4 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
connected. (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—local
underground structures such as tanks and piping systems
— rod and pipe electrodes—a 5/8 -inch (1.6-cm) solid rod or
¾-inch (1.9-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
Power and Grounding
2-13