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Chapter 1 Introduction
© National Instruments Corporation 1-9 NI 6115/6120 User Manual
Operate the product at or below the installation category
1
marked on the
hardware label. Measurement circuits are subjected to working voltages
2
and transient stresses (overvoltage) from the circuit to which they are
connected during measurement or test. Installation categories establish
standard impulse withstand voltage levels that commonly occur in
electrical distribution systems. The following is a description of installation
categories:
• Installation Category I is for measurements performed on circuits not
directly connected to the electrical distribution system referred to as
MAINS
3
voltage. This category is for measurements of voltages from
specially protected secondary circuits. Such voltage measurements
include signal levels, special equipment, limited-energy parts of
equipment, circuits powered by regulated low-voltage sources, and
electronics.
• Installation Category II is for measurements performed on circuits
directly connected to the electrical distribution system. This category
refers to local-level electrical distribution, such as that provided by a
standard wall outlet (for example, 115 V for U.S. or 230 V for Europe).
Examples of Installation Category II are measurements performed on
household appliances, portable tools, and similar products.
• Installation Category III is for measurements performed in the building
installation at the distribution level. This category refers to
measurements on hard-wired equipment such as equipment in fixed
installations, distribution boards, and circuit breakers. Other examples
are wiring, including cables, bus-bars, junction boxes, switches,
socket-outlets in the fixed installation, and stationary motors with
permanent connections to fixed installations.
• Installation Category IV is for measurements performed at the primary
electrical supply installation (<1,000 V). Examples include electricity
meters and measurements on primary overcurrent protection devices
and on ripple control units.
1
Installation categories, also referred to as measurement categories, are defined in electrical safety standard IEC 61010-1.
2
Working voltage is the highest rms value of an AC or DC voltage that can occur across any particular insulation.
3
MAINS is defined as a hazardous live electrical supply system that powers equipment. Suitably rated measuring circuits may
be connected to the MAINS for measuring purposes.