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Chapter 1 Introduction
SCB-68 Shielded Connector Block User Manual 1-12 ni.com
• Pollution Degree 3 means that conductive pollution occurs, or dry,
nonconductive pollution occurs that becomes conductive due to
condensation.
Clean the SCB-68 with a soft nonmetallic brush. Make sure that the
SCB-68 is completely dry and free from contaminants before returning it
to service.
You must insulate signal connections for the maximum voltage for which
the SCB-68 is rated. Do not exceed the maximum ratings for the SCB-68.
Remove power from signal lines before connecting them to or
disconnecting them from the SCB-68.
Operate the SCB-68 only at or below the installation category stated in
Appendix A, Specifications.
The following is a description of installation categories:
• Installation Category I is for measurements performed on circuits not
directly connected to MAINS
1
. This category is a signal level such as
voltages on a printed wire board (PWB) on the secondary of an
isolation transformer.
Examples of Installation Category I are measurements on circuits not
derived from MAINS and specially protected (internal)
MAINS-derived circuits.
• Installation Category II is for measurements performed on circuits
directly connected to the low-voltage installation. This category refers
to local-level distribution such as that provided by a standard wall
outlet.
Examples of Installation Category II are measurements on household
appliances, portable tools, and similar equipment.
• Installation Category III is for measurements performed in the building
installation. This category is a distribution level referring to hardwired
equipment that does not rely on standard building insulation.
Examples of Installation Category III include measurements on
distribution circuits and circuit breakers. Other examples of
Installation Category III are wiring including cables, bus-bars,
junction boxes, switches, socket outlets in the building/fixed
1
MAINS is defined as the electricity supply system to which the equipment concerned is designed to be connected either for
powering the equipment or for measurement purposes.