Installation guide

Elements of Network Planning
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V In addition to the minimum separation, if the cable must cross
power wiring carrying over 480 volts, it must cross only at a right
angle. The cable must not run parallel to the power wiring.
2.3.3 Adding Service Connectors
In addition to the drop cables to the network node devices required for
your application, you should provide one or more drops to allow for
service access to the active network.
You should include at least one drop at a location that will allow
connection of a device for future monitoring and servicing, without
disconnecting some active device. This can also assist in debugging
your application at the present time and for future expansion.
Caution: Before you connect or disconnect any device on an
active network, you should be aware of its effect on network
timing. See Chapter 3 for further information about
predicting network throughput and node dropout latency
time.
2.3.4 Dual-Cable Length Considerations
Designing your network as a dual-cable layout can give you increased
protection against communication errors caused by cable breakage or
excessive electrical interference. If a fault occurs on either cable path,
the node devices can continue processing error-free messages on the
alternate path.
To minimize the chance of simultaneous interference or damage to both
cables, you should route the two cables through separate areas of your
plant site. Typically this will require you to plan different lengths for
the two cable paths between successive nodes. Additional
considerations apply when the two cable lengths will not be the same.
Between any two nodes on the same cable section, the difference
between the lengths of cables A and B must not exceed 500 ft (150 m).
Figure 26 shows an example of an illegal configuration. Even though
the two cable lengths between nodes 1 ... 4 are identical at 1200 ft
(360 m), several illegal lengths exist in this configuration.
V Between nodes 1 and 2, the difference in lengths between cables A
and B is 600 ft (180 m). This exceeds the maximum allowable
difference of 500 ft (150 m).