IEEE S.F. Bay Area Council e-GRID's
BayAreaTech

THURSDAY June 21, 2012
OEB Industry Applications Chapter
Speaker: Jim Hoyt, Harold Wells Associates
Time: No-host social at 5:30 PM; Presentation at 6:15 PM; Dinner at 7:15 PM; Presentation continues at 8:00 PM
Cost: $25 for IEEE members, $30 for non-members, $15 for student and retired members
Place: Zio Fraedos, 611 Gregory Lane, Pleasant Hill
RSVP: by June 18 by email to Michael Nakamura, mnakamur@ebmud.com or phone: (510) 287-2066
Web: www.e-grid.net/docs/1206-oeb-ias.pdf

Recent changes to the NEC require the selective coordination of overcurrent protective devices at hospitals and other mission-critical facilities. Transfer switches with 30-cycle closing and withstand ratings dramatically simplify designing to that requirement.  Selective coordination was first required by the NEC in 1993 for elevator circuits.  Amendments to the code in 2005 and 2008 strengthened the requirements and expanded them to include emergency and legally required standby systems, as well as critical operations power systems.  Selective coordination, as defined in 2008 NEC, is the “localization of an overcurrent condition to restrict outages to the circuit or equipment affected, accomplished by the choice of overcurrent protective devices and their ratings or settings.”  It is a complicated process of coordinating the ratings and settings of overcurrent protective devices, such as circuit breakers, fuses, and ground fault protection relays, to limit overcurrent interruption (and the resultant power outages) to the affected circuit or equipment (the smallest possible section of a circuit).  In other words, the only overcurrent protective device that should open is the device immediately “upstream” from the circuit/equipment experiencing an overcurrent condition.
The 30-cycle transfer switch holds tremendous promise as perhaps the single most effective and simple solution to the complex challenges of selective coordination.  The right 30-cycle switch can simplify a backup power system’s design and offer more reliable protection.  Plus, it provides unmatched flexibility for future systems upgrades and expansions.