Rockwell Automation Allen-Bradley 1305-AA02A, Installation Instructions Manual

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3-4 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 three types:
•
Ungrounded Scheme
•
Scheme with High Resistance Ground
•
Fully Grounded Scheme
An ungrounded scheme, as shown in Figure 3.2 , does not provide a direct
path for the common mode noise current, causing it to seek other
uncontrolled paths. This causes related noise issues.
Figure 3.2 Ungrounded Scheme
A scheme with a high resistance ground, shown in Figure 3.3 , provides a
direct path for common mode noise current, like a fully grounded scheme.
Designers, who are concerned with minimizing ground fault currents,
commonly choose high resistance ground schemes.
Figure 3.3 Scheme with High Resistance Ground
A fully grounded scheme, shown in Figure 3.4 , provides a direct path for
common mode noise currents.Allen-Bradley strongly recommends the use
of grounded neutral systems for the following reasons:
– Controlled path for common mode noise current
– Consistent line to ground voltage reference, which minimizes
insulation stress
– Accommodation for system surge protection schemes
Earth Ground Potential
Earth Ground Potential