Critical Power: Selective Coordination

Thursday, Nov. 13, 2014, at 11 a.m. PT /1 p.m. CT/2 p.m. ET
1 AIA CES accredited LU available for attendees

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Selective coordination is a means of localizing an overcurrent condition to restrict electrical outages to the affected equipment, circuit, or feeder. In a properly coordinated system, a fault induces operation of the nearest device on the line side of the fault and limits the outage to only the faulted portion of the system. If overcurrent devices are not selectively coordinated, the fault has the potential to impact one or several devices upstream resulting in a much larger scale outage than necessary for system protection. In extreme cases faults can open the main overcurrent protective device and cause an outage for the entire facility.

Both emergency and legally required systems are required to be selectively coordinated to ensure only the closest upstream device from an electrical fault operates. Optional standby loads should be selectively coordinated to ensure faults do not result in business lost revenue. Selective coordination requires analysis of time-current curves of overcurrent protective devices—both fuses, circuit breakers, and relays. For circuit breakers both fixed and adjustable parameters must be clearly understood to ensure selective coordination can be achieved.

Ground fault protection settings must also be scrutinized as they are a very typical source of nuisance trips often at the building service level. Some documentation, specifically with British Standards, refers to selective coordination as “discrimination.”  

Learning objectives:


Moderator: Jack Smith, Consulting-Specifying Engineer, Pure Power, and CFE Media, LLC

Sponsors: ABB Low Voltage Products, ASCO, Generac Industrial Power, NFPA

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