Rockwell Automation 1336T Wiring and Grounding Guide, (PWM) AC Drives - Manual (Page 52)

52 Rockwell Automation Publication DRIVES-IN001M-EN-P - March 2014
Chapter 3 Grounding
The grounding scheme can greatly affect the amount of noise and its impact on
sensitive equipment. The power scheme is likely to be one of these three types:
• Ungrounded scheme
• Scheme with high resistance ground
• Fully grounded scheme
An ungrounded scheme ( Figure 16 ) does not provide a direct path for the
common mode noise current, causing the current to seek other uncontrolled
paths. This causes related noise issues.
Figure 16 - Ungrounded Scheme
A scheme with a high resistance ground ( Figure 17 ) provides a direct path for
common mode noise current, like a fully grounded scheme. Designers that are
concerned with minimizing ground fault currents commonly choose high
resistance ground schemes.
Figure 17 - Scheme with High Resistance Ground
A fully grounded scheme ( Figure 18 ) provides a direct path for common mode
noise currents. The use of grounded neutral systems is recommended for these
reasons:
• Controlled path for common mode noise current.
• Consistent line-to-ground voltage reference that minimizes insulation
stress.
• Accommodation for system surge protection schemes.
Earth Ground Potential
Earth Ground Potential