Specifications

Chapter 4 - Transient Protection of RS-422 and RS-485 Systems RS-422 And RS-485 Applications Ebook
Page 63 of 137 Manual Documentation Number: <DocNumber>
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recommended to add a fuse type device in addition to shunting type
suppression.
Figure 47: Fused Port Protection
When a short circuit occurs, the shunt suppression will begin
conducting, but shunting by itself cannot withstand the steady state
currents of this type of surge. A small enough fuse value should be
chosen so that the fuse will open before the shunt device is damaged.
A typical fuse value is 125 mA.
Choosing the right protection for your system
While it is difficult to predict what type and level of isolation is correct
for a system, an educated guess should be made based on the
electrical environment, physical conditions and cost of failures in
downtime and repair costs. Systems connected between two power
sources, such as building to building, office to factory floor, or any
system covering long distances should require some level of transient
protection. The following table compares transient protection
techniques.