AC-2000
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8.10/8.11
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7 ELECTRICAL GROUNDING
CAUTION Always connect temperature and sensor shields to earth ground.
Avoid mixing high voltage wiring with sensor and low voltage wiring.
Keep the controller as far as possible from heavy contactor boxes and other sources of
electrical interference.
7.1 Ground Rods
Ground rods are used to efficiently connect the system to earth where current may be dissipated in the soil.
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Material
: Ground rods should be copper clad or galvanized steel.
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Diameter
: Minimum 5/8”, preferably 3/4”. Generally the larger the rod diameter, the lower it’s
resistance to current flow.
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Length
: Minimum 2.5 meters (8 feet), preferably 3-meter (10-foot). A longer ground rod will
reach a soil with higher moisture content. Moist soil carries current much better than drier soil.
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Single grounding
: It is important that there is only one grounding location where a rod or series
of rods are connected to each other using a ground wire.
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Independent ground rods will increase the risk of current, from a lightning strike for example,
being dissipated through one rod and reentering the system through an adjacent rod.
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Location
: Close to the main circuit breaker panel and in moist soil. For example in an area that is
usually wet from a drip or a low spot where water drains. Make sure the area is well protected
from damage by lawnmowers, tractors, etc’.
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Rod installation
: Drive the rod into the earth until about 10 cm (4 inches) is left above grade. If it
is impossible to drive the rod to the proper depth, it is acceptable to lay the rod horizontally, 80 cm
(2.5 feet) below grade.
In case the rod is exposed to damage, for example by lawnmowers or tractors it can be installed in a hole,
about 20 cm (8 inches) deep so that the rod is about 10 cm under grade and 10 cm above hole level.
The National Electric Code (NEC) mandates two ground rods unless you can show less
than 10 ohms resistance with one rod.
7.2 Ground Wire
The ground wire is a large copper wire that connects the main circuit breaker panel to the ground rod.
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Material
: Ground rods should be copper clad or galvanized steel.
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Diameter
: Typically, 16 mm (6-gauge) copper wire is sufficient. If the wire run is greater than 20
feet, 20 mm (4-gauge) wire should be used.
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Length
: Minimum 2.5 meters (8 feet), preferably 3-meter (10-foot). A longer ground rod will
reach a soil with higher moisture content. Moist soil carries current much better than drier soil.
The ground wire should be protected from damage by lawnmowers, tractors, etc’. It should be buried
minimum 15 cm (6 inches) under grade for protection and enter the house as soon as possible. It is
important that the wire not be cut; it should remain continuous.
7.3 Ground Clamps
Ground wires should not be merely wrapped around a ground rod. Ground clamps are used to attach a
ground wire to a ground rod. The most common clamp is known as an acorn clamp. Make sure the ground
clamps you select are rated for outdoor use. Do not use pipe clamps rated for inside water lines or hose
clamps to attach the ground wire.
