separated to allow a low-impedance connection, or if equipment or support structures are at
high risk of a direct lightning strike.
In very dry desert or in polar environments with no liquid water, a true earth ground
connection may not be possible. The system can function well in isolation as long as there is a
low-impedance connection between the case grounds of all pieces of equipment.
For safety reasons, equipment should be connected to earth ground wherever possible.
B.2 Grounding the Sensor in a Direct Burial Installation
Use the guidelines in this section to ground a Trillium Compact Posthole that is installed in an
uncased hole.
In a direct burial installation the seismometer itself provides the system earth ground. When
the case of the seismometer and all other equipment is connected to the case ground of the
digitizer via shielded cables as provided by Nanometrics, this implements a correct grounding
scheme as described in "Grounding Scheme" on the previous page. See Figure B-1.
If the Trillium Compact Posthole seismometer is installed in a cased hole, ground the system as
described in "Grounding the Sensor in a Metal-cased Hole Installation" on the next page.
In a test lab installation, a Trillium Compact Posthole system should be grounded as described
in "Grounding the Sensor in a Vault or Test Lab Installation" on page93.
Appendix B - Grounding guidelines
16889R10 • 2020-11-12 Page 90
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