In the Zone of Applying Zone Selective Interlocking (ZSI)
Rejuvenating ZSI to help create a safer future in electrical distribution systems.

Thursday, August 30, 2018, at 11 a.m. PT/1 p.m. CT/2 p.m. ET
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Zone Selective Interlocking (ZSI) has existed for more than 40 years, but yet so many people in the electrical field have little knowledge about what it is and how it works.

ZSI is a network of two or more interconnected circuit breakers that communicate with each other so that a short circuit or ground fault will be cleared by the breaker closest to the fault in the minimum time possible. The primary goal of ZSI is to switch off the fault current within the shortest possible time under consideration of full selectivity, regardless of the fault location in an electrical distribution system.

ZSI provides the complete range of selectivity with an extremely short delay time of 50ms minimum typically regardless of the number of fault zones and the location of the short circuit or ground fault in the power distribution system. The benefits of ZSI become more apparent with a higher number of fault zones which are typically found in large systems. By shortening the time to clear the fault, ZSI significantly reduces stress and damage in the event of a short circuit in the electrical apparatus. As described in NEC 240.87, ZSI is also a method suitable for compliance with that section of the code.

Topics that will be covered during the webcast: 

1.    Applying ZSI in Arc-Reduction and Selective Coordination circuits
2.    How do breakers communicate and connect in a ZSI network
3.    Illustrations and Comparisons of ZSI with Time Current Curves
4.    Understanding the fault protection sequences of ZSI
5.    General Cost Impact.  


  • Roy Hicks IV, Business Development Manager, Siemens (Presenter)
  • Robert W. Jensen, P.E., Business Development Manager (Presenter)
  • Rick Pinchard, Business Development Manager (Q&A)

Moderator: Jack Smith, Content Manager, CFE Media

Sponsor: Siemens 

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