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Chapter 2 Configuration and Installation
© National Instruments Corporation 2-3 NI 7340 User Manual
Remove power from signal lines before connection to or disconnection
from the device.
Caution National Instruments measurement products may be classified as either
Installation Category I or II. Operate products at or below the Installation Category level
specified in the hardware specifications.
Installation Category
1
: 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 Category establishes
standardized impulse withstand voltage levels that commonly occur in
electrical distribution systems. The following is a description of Installation
(Measurement
3
) Categories:
• Installation Category I is for measurements performed on circuits not
directly connected to the electrical distribution system referred to as
MAINS
4
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 (e.g., 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
1
Installation Categories as 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
Installation Category is also referred to as Measurement Category.
4
MAINS is defined as the (hazardous live) electrical supply system to which equipment is designed to be connected for the
purpose of powering the equipment. Suitably rated measuring circuits may be connected to the MAINS for measuring
purposes.