SCXI-1356 Shielded Cable Installation Guide
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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 installation, and
equipment for industrial use, such as stationary motors with a
permanent connection to the building/fixed installation.
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Installation category IV is for measurements performed at the source
of the low-voltage (<1,000 V) installation.
Examples of category IV are electric meters, and measurements on
primary overcurrent protection devices and ripple-control units.
Below is a diagram of a sample installation.
Electric
Meter
Circuit
Breaker
Plug-in
Equipment
Category IV
Category III
Category II
Category I
Source of
Low-Voltage
(<1000 V)
Installation
Building/Fixed
Installation
Distribution
Panel
Local-Level
Distribution, such
as Wall Sockets
Secondary
Windings of
Isolation
Transformers
