National Instruments FieldPoint cFP-21 Series Quick Start Manual page 19

324033b.fm Page 19 Wednesday, September 14, 2005 2:09 PM
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
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
1
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.
© National Instruments Corporation 19 cFP-21xx Quick Start Guide
1