Critical Power: Circuit protection

Thursday, Nov. 3, 2016, 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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Although a building’s entire electrical distribution system is important, its overcurrent protection is the most critical to safety. Overcurrent includes short circuits and overloads. During a short circuit, electrical current bypasses the load, taking the path of least resistance. An overload is an overcurrent condition within normal current paths. If an overload is allowed to persist, it can cause equipment or wiring damage and potentially start a fire. Temporary overloads can be harmless; sustained overloads can cause damage. Temporary overloads occur frequently, are often a routine part of system startup or operation, and should be allowed to subside. An overcurrent protective device (OCPD) should not open the circuit during normal operation, allowing motors to start and loads to stabilize.

Overcurrent scenarios dictate the type of overcurrent protection that should be used. NFPA 70: National Electrical Code (NEC) has established basic power system overcurrent protection requirements and recognizes fuses and circuit breakers as the two of the basic types of OCPDs. Fuses and circuit breakers are available in a variety of sizes and ratings. Their similar—yet different—features and characteristics allow electrical system designers to choose devices appropriate for a facility’s electrical system.

Learning objectives: 

  • Explain the applicable codes and standards including NFPA 70: National Electrical Code (NEC).
  • Analyze and compare the differences between using fuses, circuit breakers, and other overcurrent protective devices (OCPD) to protect transformers, switchgear, feeders, branches, and equipment.
  • Consider the importance of proper grounding in circuit protection.
  • Outline the coordination, overcurrent, short-circuit, and ground-fault protection issues for non-residential facilities.


  • Tom Earp, PE, ATD, principal/MEP engineering director, Page, Austin, Texas
  • John Yoon, PE, LEED AP ID+C, lead electrical engineer, McGuire Engineers Inc., Chicago

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

Sponsor: Eaton

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