cFP-21xx Quick Start Guide 20 ni.com
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
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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 (for example, 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.
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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.
