National Instruments NI PCIe-8231

Caution National Instruments measurement products may be classified as either

Measurement Category I or II. Operate products at or below the Measurement Category

level specified in the hardware specifications.

Measurement Category1: Measurement circuits are subjected to working

voltages2 and transient stresses (overvoltage) from the circuit to which they

are connected during measurement or test. Measurement Category

establishes standardized impulse withstand voltage levels that commonly

occur in electrical distribution systems. The following is a description of

Measurement (Installation3) Categories:

• Measurement Category I is for measurements performed on circuits

not directly connected to the electrical distribution system referred to

as MAINS4 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. 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 Measurement Category II are measurements performed

on household appliances, portable tools, and similar products.

• 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 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 Measurement Category is also referred to as Installation 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.