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Setup and Connection
2.7.2 Noise Reduction Techniques
For proper test results it is important to consider the following:
• If possible, disconnect both primary terminals of the CT from the utility lines.
• If possible, always use the original coax measurement cables delivered by
OMICRON. If it is necessary to use loose single-wire measurement cables,
twist the wires to a twisted-pair line. Avoid open loops consisting of individual
single-wire measurement cables in order to prevent interference voltages
caused by magnetic fields.
• Connect one terminal of the CT’s primary side to protective earth. If it is not
possible to disconnect the utility lines from both primary terminals, connect
that side of the primary circuit that is able to receive more interferences to PE
(the primary side that is still connected to the utility lines or the side with the
longer line length, respectively). The ungrounded side should be the side that
receives less interferences.
• When testing a CT in a utility, take care that one side of the CT is connected
to PE and at least the ungrounded terminal is disconnected from all utility
lines.
Refer to Figure 2-20.
Note: Do not connect both primary terminals to PE! This would cause
incorrect measurement results. Connecting both primary terminals to PE has the
same effect as a short-circuit in the CT.
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