Rockwell Automation 1336T Wiring and Grounding Guide, (PWM) AC Drives - Manual (Page 49)

Rockwell Automation Publication DRIVES-IN001M-EN-P - March 2014 49
Chapter
3
Grounding
This chapter discusses various grounding schemes for safety and noise reduction.
An effectively grounded scheme or 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 that can result in undue hazard to connected equipment or to persons
(as defined by the US National Electric Code NFPA70, Article 100B).
Grounding of a drive or drive system is done for two basic reasons: safety (as
defined above), and noise containment or reduction. While the safety ground
scheme and the noise current return circuit can sometimes share the same path
and components, they are considered different circuits with different
requirements.
Grounding Safety Grounds The object of safety grounding is to make sure 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 regulations and
codes vary based on country, type of distribution system, and other factors.
Periodically check all ground connections and verify that the connections are
secure and correct.
General safety requires that all metal parts are connected to earth with separate
copper wire, or wires of the appropriate gauge. Always follow any specific
directions for connecting a safety ground or protective earth (PE) directly to any
piece of equipment.
Building Steel
If intentionally bonded at the service entrance, the incoming supply neutral or
ground is bonded to the building ground. Building steel is typically the best
representation of ground or earth. The structural steel of a building is generally
bonded together to provide a consistent ground potential. If other means of
grounding are used, such as ground rods, you must understand the voltage
potential between ground rods in different areas of the installation. The type of
soil, ground water level, and other environmental factors can greatly affect the
voltage potential between ground points if they are not bonded to each other.