©
National Instruments Corporation
3
HDD-8263/8264 Installation Guide
You
must
insulate signal connections for the maximum voltage for which
the module is rated. Do
not
exceed the maximum ratings for the module.
Do not install wiring while the module is live with electrical signals. Do not
remove or add connector blocks when power is connected to the system.
Avoid contact between your body and the connector block signal when hot
swapping modules.
Remove power from signal lines before connecting
them to or disconnecting them from the module.
Operate the module at or below the
measurement 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. Measurement categories establish
standard impulse withstand voltage levels that commonly occur in
electrical distribution systems. The following is a description of
measurement categories:
•
Measurement 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.
•
Measurement Category II is for measurements performed on circuits
directly connected to the electrical distribution system (MAINS
3
).
This category refers to local-level electrical distribution, such as that
provided by a standard wall outlet (for example, 115 AC voltage for
U.S. or 230 AC voltage for Europe). Examples of Measurement
Category II are measurements performed on household appliances,
portable tools, and similar modules.
•
Measurement 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.
•
Measurement 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
Measurement categories, also referred to as
installation 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.
