Cable Splicing And Termination; Lightning Protection - Geokon 4200 Series Instruction Manual

9

4.5 Cable Splicing and Termination

Terminal boxes with sealed cable entries are available from Geokon for all types of applications.
These allow many gages to be terminated at one location with complete protection of the lead
wires. The interior panel of the terminal box can have built-in jacks or a single connection with a
rotary position selector switch. Contact Geokon for specific application information.
Because the vibrating wire output signal is a frequency rather than a current or voltage,
variations in cable resistance have little effect on gage readings; therefore, splicing of cables has
no ill effects, and in some cases may in fact be beneficial. The cable used for making splices
should be a high quality twisted pair type, with 100% shielding and an integral shield drain wire.
When splicing, it is very important that the shield drain wires be spliced together. Always
maintain polarity by connecting color to color.
Splice kits recommended by Geokon incorporate casts, which are placed around the splice and
are then filled with epoxy to waterproof the connections. When properly made, this type of splice
is equal or superior to the cable itself in strength and electrical properties. Contact Geokon for
splicing materials and additional cable splicing instructions.
Cables may be terminated by stripping and tinning the individual conductors and then connecting
them to the patch cord of a readout box. Alternatively, a connector may be used which will plug
directly into the readout box or to a receptacle on a special patch cord.
The cable from the strain gages can also be protected by the use of flexible conduit, which can be
supplied by Geokon.

4.6 Lightning Protection

Unlike numerous other types of instrumentation available from Geokon, embedment strain gages
do not have any integral lightning protection components, such as transorbs or plasma surge
arrestors. Usually this is not a problem, as these types of gages are installed within concrete or
grout and somewhat isolated from potentially damaging electrical transients. However, there
may be occasions where some sort of lightning protection is desirable, for example, where the
gage is in contact with rebar that may be exposed to direct or indirect lightning strikes. In
addition, if the instrument cable is exposed, it may be appropriate to install lightning protection
components, as the transient could travel down the cable to the gage and possibly destroy it.