Terms And Definitions - Allen-Bradley 2711P Technical Data Manual

Wiring and Grounding Guidelines for PanelView Plus Terminals 3

Terms and Definitions

This section provides a list of important terms and definitions referred to in this
document.
UL Class 2 - A UL Class 2 power supply meets the requirements of UL 1310,
Class 2 Power Units. A Class 2 power source has a 'Class 2' marking and UL
symbol on its nameplate. Such a supply, when properly applied, provides output
power that is safe from electrical shock and fire hazard.
Safety Extra-low Voltage (SELV) - An electrical secondary circuit in which the
voltage cannot exceed a safe value under normal and single-fault conditions,
including earth faults in other circuits. SELV is defined in IEC EN60950 and
IEC EN60364-4-41.
The voltage between any two conductors in a SELV circuit, and the voltage
between any conductor and earth, cannot exceed 30V rms, 42.4V AC peak, or
60V DC under normal operating or single-fault conditions.
SELV Power Source - A power source determined by a regulatory body to meet
SELV requirements.
Protective Extra-low Voltage (PELV) - A safety extra-low voltage output with
its common connected to earth ground.
Earth/Ground - A conducting path between an electric circuit or equipment
and ground for safety or EMC reduction. In industrial equipment, the earth
connection is typically a grounded metal bar with features to facilitate connecting
to multiple pieces of equipment.
DC Common - For PanelView Plus terminals that operate on 24V DC power,
DC common is the conductor that returns 24V DC current to the source supply,
and is connected to the DC(-) position on the input power terminal block.
Functional Earth (FE) Conductor - A conductor that is in electrical contact
with Earth for interference immunity improvement.
Protective Earth (PE) Conductor - A conductor that is in electrical contact
with Earth for safety protection against electrical shock.
Ground Bus - The system ground bus is a metal bar in the enclosure whose
purpose is to provide a grounding point for the equipment that comprises the
system. The ground bus has multiple features to facilitate grounding multiple
pieces of equipment. The ground bus is connected to the grounding electrode
system via the grounding electrode conductor.
In typical industrial systems, the ground bus is mounted on the back panel of the
enclosure. The protective earth and functional earth terminals of the various
equipment in the enclosure are connected to the ground bus bar.
Rockwell Automation Publication 2711P-TD001D-EN-P - February 2011