Improving Electrical Safety With Short Circuit Protection


Increasing concern for arc flash safety has grown to include both operators of electrical equipment as well as electrical workers. Internal arc faults can blow open doors of low voltage equipment including motor control centers (MCC) that have been properly installed. Should this occur when an operator is interacting with the equipment, the worker can very easily be exposed to the hazards of arc flash. To protect workers without arc-rated PPE, ‘arc resistant’ low voltage MCCs have been tested according to an IEEE standard to prove that the MCC contains the hazards of arc flash should an arc fault occur with the doors properly closed. Additionally, many companies are focusing efforts to get lower incident energy levels on equipment that has frequent worker interaction with the doors open. Many are seeking the lowest values that are economically feasible. 

Maintaining continuity of power to critical loads requires a system view when deciding on overcurrent protective devices (OCPD) to protect against arc flash. Continuity of service requires that feeder OCPD allow MCC branch devices to clear faults within their zone of protection. If this requires that the upstream feeder OCPD has a delay added to its trip, incident energy levels at the downstream MCC will be increased. Thus, decisions about OCPDs within the MCC can indirectly affect the levels of incident energy at the MCC. Since current limiting fuses can be coordinated within their short circuit region without any intentional delay, it is possible to dramatically limit the energy delivered to arcing faults without compromising continuity of service because of a short circuit event. Class L and J fuses can limit incident energy throughout the MCC to well below the accepted 2nd degree burn threshold of 1.2 cal/cm2. Properly sized Class J fuses can also minimize damage to faulted branch circuit equipment and provide the best protection of components in the fault path. 

This training will provide background information on NFPA requirements regarding workers “exposed to the arc flash hazard.” In addition to protection of workers, coverage of the selection of current limiting fuses for a long reliable life and optimum protection of the MCC will be provided. An ‘Arc Resistant’ low voltage MCC will be introduced with a focus on how a ‘Device Limited’ Arc Resistant LV MCC can provide maximum safety benefits.


Mike Lang, Principal Field Engineer for Mersen, has participated in over1,000 arc flash tests in Mersen’s high power test lab as leader of theMersen arc flash team. He has coauthored several prize-winning IEEEpapers on arc flash including papers at the 2006 PCIC Conference, the2008 PPIC Conference and 2016 PPIC Conference. He was also awardedthe 2011 I&CPS Ralph H. Lee Department Prize Paper Award for his workon 208V arc flash research. He recently received the 2018 Technical Awardfor Excellence in Prevention Through Design by the Electrical SafetyCommittee of the IEEE Industrial Application Society. 

Mike is currently co-chairman of the IEEE/NFPA Collaboration on ArcFlash Research effort and has served as a member of the Research, Testand Planning Committee and on the Technical Advisory Committee as partof Mersen’s Platinum sponsorship of the Collaborations research. Mike isan active member of the IEEE 1584 Working Group.

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Additional Information:

This is a two day seminar with part one on 5/4/2021 from 11:00 am - 12:00pm EDT and part two on 5/5/2021 from 11:00 am - 12:00pm EDT

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