© Munters AB, 2016 24
6 Electrical grounding for controllers
Electrical equipment can be destroyed or slowly damaged by voltage spikes, lightning hits, etc.
Proper electrical grounding in combination with the SMART-8C/3MD internal protections is essential
to protect the system, reduce the risk of damage and prolong its lifetime. Correct selection and
installation of equipment will protect your system and reduce the risk of human injury.
Proper grounding provides an easy path for electrical current to return to its source. A grounding
system should tie all non-current carrying conductors to earth ground (0 volts). The grounding system
should present a minimum resistance to current flow. Make sure all items used are in proper
condition; for example, a corroded wire clamp attaching a ground wire to a ground rod might add
100 ohms or more resistance to a system. Less than 5 ohm will be considered a good ground.
6.1 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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: Ground rods should be copper clad or galvanized steel.
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: Minimum 5/8”, preferably 3/4”. Generally the larger the rod diameter, the
lower its resistance to current flow.
•
: Minimum 2.5 meters (8 feet), preferably 3-meter (10-feet). A longer ground rod
will reach a soil with higher moisture content. Moist soil carries current much better than
drier soil.
•
: 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.
•
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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: 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.
•
: 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.
NOTE The National Electric Code (NEC) mandates two ground rods unless you can show
less than 10 ohms resistance with one rod.
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