Campbell Scientific CR1000 Measurement and Control System - Manual (Page 87)

Section 7. Installation
87
protection at installation. Spark-gap protection is usually an option with these
products, so it should always be requested when ordering. Spark gaps for these
devices must be connected to either the earth ground lug, the enclosure ground, or
to the earth (chassis) ground.
A good earth (chassis) ground will minimize damage to the datalogger and
sensors by providing a low-resistance path around the system to a point of low
potential. Campbell Scientific recommends that all dataloggers be earth (chassis)
grounded. All components of the system (dataloggers, sensors, external power
supplies, mounts, housings, etc.) should be referenced to one common earth
(chassis) ground.
In the field, at a minimum, a proper earth ground will consist of a 6- to 8-foot
copper-sheathed grounding rod driven into the earth and connected to the CR1000
Ground Lug with a 12-AWG wire. In low-conductive substrates, such as sand,
very dry soil, ice, or rock, a single ground rod will probably not provide an
adequate earth ground. For these situations, search for published literature on
lightning protection or contact a qualified lightning-protection consultant.
In vehicle applications, the earth ground lug should be firmly attached to the
vehicle chassis with 12-AWG wire or larger.
In laboratory applications, locating a stable earth ground is challenging, but still
necessary. In older buildings, new ac receptacles on older ac wiring may indicate
that a safety ground exists when, in fact, the socket is not grounded. If a safety
ground does exist, good practice dictates the verification that it carries no current.
If the integrity of the ac power ground is in doubt, also ground the system through
the building plumbing, or use another verified connection to earth ground.