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19 littelfuse.com the potential reality of inductive surge risks. Additionally, wherever a human might touch something related to the system, you need to be aware of electrostatic discharge (ESD) in the interfacing. One needs to be mindful of that wherever a motor's stop and start can cause fast electrical transients. This leads to several specific challenges that the designer must take into account. For example, one of the difficulties is lightning surges. Lightning surges can significantly impact ports that one is attempting to protect. Another item is induced power surges. From lightning strikes, induced power surges can come through other lines and cause an impact on ports that you want to protect. ESD, such as a human touching component, can cause high voltage going into your component. If someone inadvertently miswired something, an improperly connected cable can cause damage to equipment by sending too much voltage or current. Additionally, fast electrical transients can arise when someone stops or starts a big motor or other kinds of equipment. These transients are often called bouncing. Finally, one often might experience problems if and when cables wear into a break, and they can send wrong power to a port. These issues can be addressed or reduced by wire ties and other methods that can minimize through-the-system vibrations. Figure 1: RS-485 Intra-building (Source: Littelfuse) Figure 2: RS-485 Outdoor (Source: Littelfuse) RS-485 Protection RS-485 is commonly employed in buildings (Figure 1). Littelfuse has a wide variety of products and technologies that provide intra-building protection. A resettable polymeric positive temperature coefficient (PPTC) or PolySwitch ® positive temperature coefficient can protect against both short circuit and power crosses. For voltage protection, the TVS Diode array works well. Littelfuse offers the SM712 designed explicitly for RS-485 and protects against ESD, electrical fast transcends, and some lightning- induced surges. As an alternative, one can use a Pulse-Guard ESD Suppressor type PGB or XGD as other alternatives. These all help designers align too many IEC, ITU, GR, and UL standards. But what should the designer employ if the solution is not within the building but rather outdoors and in a harsher environment? Indeed, one is going to need more protection in these environments (Figure 2). One can still employ resettable PPTCs to protect against short-circuit and power crosses. For lightning protection, Littelfuse offers a combination of a Gas Discharge Tube (GDT) with a SIDACtor ® . With a lightning surge, SIDACtor will fire quickly. This will cause more voltage across the PPTC and, at that point, the GDT will fire. The resistance of the PPTC must be