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 which may 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 2 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.
Building Steel
If intentionally bonded at the service entrance, the incoming supply neutral
or ground will be bonded to the building ground. Building steel is judged to
be 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, the
user should understand the voltage potential, between ground rods in
different areas of the installation. 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.
Summary of Contents for Allen-Bradley 1305-AA02A
Page 4: ...ii Summary of Changes Notes ...
Page 40: ...2 18 Power Distribution Notes ...
Page 48: ...3 8 Grounding Notes ...
Page 68: ...4 20 Practices Notes ...
Page 78: ...6 8 Electromagnetic Interference Notes ...
Page 94: ...Glossary 4 UL Underwriters Laboratories ...
Page 100: ...Index 6 ...
Page 101: ......