Critical power: Transfer switches in switchgear

Consulting engineers must understand transfer switch types, timing requirements, ratings, and the effects that the characteristic of each emergency load has on generator operation.


Flash is required!

When an interruption of electrical power occurs, an automatic transfer switch shifts loads between utility and generator power. During these transitions, transfer switch timing and sequence is critical to ensure proper system operation. Consulting engineers must understand transfer switch types, timing requirements, ratings, and the effects that the characteristic of each emergency load has on generator operation. They must also understand how a facility's electrical system (available fault current, number of generators, paralleling configuration) affects transfer switch choices.

Learning objectives:

  • The audience will understand the applicable codes: NFPA 110: Standard for Emergency and Standby Power Systems and NFPA 70: National Electrical Code (NEC)
  • Viewers will learn about open-and closed-transition automatic transfer switching including transfer switch timing and bypass considerations
  • Viewers will learn how to properly apply transfer switches and switchgear
  • Viewers will learn how to select transfer switch timing and sequencing to assure that the generator will assume and operate the selected loads.


Ken Lovorn, PE, Lovorn Engineering Associates, Pittsburgh

Danna Jensen, PE, LEED AP BD+C, ccrd partners, Dallas

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

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