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NI PCIe-8255R User Manual
4
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occur in electrical distribution systems. The following is a description of 
Measurement (Installation
1
) Categories:
Measurement Category I is for measurements performed on circuits 
not directly connected to the electrical distribution system referred to 
as MAINS
2
 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.
Unpacking
The NI 8255R ships in an antistatic package to prevent electrostatic 
discharge from damaging device components. To avoid such damage in 
handling the device, take the following precautions:
Ground yourself via a grounding strap or by holding a grounded object, 
such as the computer chassis.
Touch the antistatic package to a metal part of the computer chassis 
before removing the device from the package.
Caution
Never touch the exposed pins of connectors.
1   
Measurement Category is also referred to as Installation Category.
2   
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.