Operator's guide
power supply will couple to the sensor.
As with AC installations, if the borehole is more than around 30 m from
the surface enclosure, you will need to provide a second earthing point
for the local ground plate.
DC power is most commonly available at self-contained installations
with power supplied from baieries, solar panels, or a wind generator.
In these cases, the power supply may already have protection from
transients installed, in which case you may not need such
comprehensive protection (although some form of protection is
always
necessary.)
External lightning protection
The surface installation building, and if possible the borehole also,
should be protected by lightning conductors. These should lead to
ground well away from the borehole. As a rule of thumb, a lightning
mast provides a “zone of protection” within a 45 ° cone the height of the
mast.
December 2004
43
