Rockwell Automation 294D ArmorStart LT Distributed Motor Controller DeviceNet Version - User Manual - Manual (Page 57)

Rockwell Automation Publication 290D-UM001A-EN-P - June 2012 57
Installation and Wiring Chapter 2
Grounding An effectively grounded product is one that is “intentionally
connected to earth
through a ground connection or connections of sufficiently low impedance and
having sufficient current-carrying capacity to prevent the buildup of voltages
which may result in undue hazard to connected equipment or to persons” (as
defined by the US National Electric Code NFPA70, Article 100B). Grounding
is done for two basic reasons: safety (defined above) and noise containment or
reduction. While the safety ground scheme and the noise current return circuit
may sometimes share the same path and components, they should be considered
different circuits with different requirements.
Grounding Safety Grounds
The object of safety grounding is to ensure that all metalwork is at the same
ground (or Earth) potential at power frequencies. Impedance between the drive
and the building scheme ground must conform to the requirements of national
and local industrial safety regulations or electrical codes. These will vary based
on country, type of distribution system and other factors. Periodically check the
integrity of all ground connections.
General safety dictates that all metal parts are connected to earth with separate
copper wire or wires of the appropriate gauge. Most equipment has specific
provisions to connect a safety ground or PE (protective earth) directly to it.
Grounding PE or Ground
The safety ground - PE must be connected to earth ground. This point must
be connected to an adjacent building steel (girder, joist), a floor ground rod, a bus
bar or a building ground grid. Grounding points must comply with national and
local industrial safety regulations or electrical codes. Some codes may require
redundant ground paths and periodic examination of connection integrity.
Grounding Motors
The motor frame or stator core must be connected directly to the PE connection
with a separate ground conductor. It is recommended that each motor frame be
grounded to building steel at the motor.
IMPORTANT To avoid electrolytic corrosion on the external earth terminal, avoid spraying
moisture directly on the terminal. When used in washdown environments
apply a sealant or other corrosion inhibitor on the external ground terminal
to minimize any negative effects of galvanic or electro-chemical corrosion.
Ground connections should be inspected on a regular basis.