Dear Friends: Same work new home. I began working with EDT in Puerto Rico in 2015. October 2017 marks the time that Columbia, South Carolina became my new home. On occasion I have felt homesick, but my wife and I have entertained ourselves exploring Columbia and other areas here in South Carolina. From our Saturday trips to the Soda City Market, or trips to Charleston and Myrtle Beach, we always try to have something new to do every weekend. And yes, we have enjoyed it. Since coming to the Columbia Office, I have had the opportunity to conduct evaluations of damaged electrical equipment and to conduct fire investigations in locations throughout South Carolina such as Aiken, Lugoff, Myrtle Beach, Hilton Head Island, Union, and Kiawah Island. Fortunately, I have had the opportunity to see new places while traveling to different work locations. Next, you will find an epistle that I have prepared related to Ground Fault Circuit Interrupters. My hope is that this will inform you about an important device that we all rely on to make our lives safer. If there is a need for services my colleagues and I could provide, contact our Columbia or Charleston Offices so we can do our best to head you in the right direction.
Edgardo Lรณpez, P.E., CFEI
Until next time, Edgardo Lรณpez, M.E., P.E. Consulting Engineer
Columbia, SC elopez@edtengineers.com
Engineering Design & Testing Corp.
GROUND FAULT CIRCUIT Interrupters
Author: Edgardo López, P.E., CFEI Columbia District Office
Electricity powers the world – our cities, factories, farms, and our appliances. Every day we use electricity without even thinking about what it is. We can’t see it and give little thought to how dangerous it can be. The average person has no idea whether a receptacle in his or her home is “on” unless something such as a television or an appliance is plugged into it and is operable. So, how do we protect ourselves when we cannot even see what it is?
ELECTRICITY Electricity is defined as the flow of current through a conductor. That flow takes place when there is a voltage difference between two points, for instance, between a hot wire and a neutral wire to which a light fixture in a home is connected. This voltage difference results in a flow of current to create light. When thinking about current flow, think about the pins on the plug at the end of an appliance electrical cord. The pair of pins correspond to the hot wire and the neutral wire. The flow of current takes place when the plug is connected to a receptacle, thus completing the circuit between the hot and neutral wire.
GROUND FAULT CIRCUIT INTERRUPTERS (GFCIs)
With electricity, there is the hazard of
an electric shock or even an electrocution. Minimization of the risk associated with this hazard is what gave rise to the development of Ground Fault Circuit Interrupters (GFCIs). Since their introduction dating back to 1961, GFCIs have served to reduce the risk of electric shocks inside and around homes. A GFCI is a device that is installed in a receptacle or a circuit breaker, or built into an extension power cord.
This device protects us from electric
shocks. The device makes a comparison between the current from the receptacle to the appliance and the current going through the system’s neutral wire. When everything is operating as intended, the same amount of current flows from the receptacle to the appliance and from the appliance to the receptacle. Should there be a difference in these current values, the GFCI stops the flow of current, creating an open circuit within the receptacle, the breaker, or the extension power cord. The interruption occurs very fast – on the order of 25 milliseconds (0.025 seconds) or less. Consider, for example, a power drill that malfunctions while in use, energizing the metal casing of the drill. The amount of current from the receptacle to the drill will equal the sum of the current that returns from the drill to the receptacle and the current flowing through the person using the drill to ground. An electrical shock would be felt by the person due to the current flowing through him or her to ground. However, had the drill been connected to a GFCI, the GFCI would have sensed the amount of current difference returning to the receptacle and would have tripped, opening the circuit and stopping the current flow. The response would be fast enough to prevent the electric shock.
GFCIs contain the following components: a differential current transformer (current transformer), a trip solenoid, a trip mechanism, and test and reset buttons. The current transformer serves to compare the current flowing in and out of the appliance. When there is a difference in current flow, the trip solenoid reacts and sends a signal to the trip mechanism to open the circuit. The test and reset buttons in GFCIs are used to provide a means to externally test the functionality of the device. When the test button is depressed, a GFCI acts as though the device has detected a current flowing to ground. A GFCI in working order will stop the current flow. The reset button is used to return the GFCI to operating condition after the GFCI has been tested. A requirement for GFCIs was first added to the National Electric Code (NEC) in 1971. The requirement began with single-phase receptacles in use at construction sites. Requirements expanded over time. In subsequent NEC editions, many other locations were addressed where the hazard of an electrical shock could be present. Today, GFCIs are required in locations such as kitchens, bathrooms, outdoor areas, garages, crawlspaces, basements, boathouses, and laundries. It would be an understatement to say that many lives have been saved or injuries avoided since GFCI protection requirements were introduced. From an electrical engineering perspective, the GFCI is a valuable protective device that has accomplished its purpose of safeguarding people from the hazards of using electricity in their daily lives.
Columbia, South Carolina District Office | Engingeering Design & Testing Corp.
Edgardo López, P.E., CFEI Discipline: Electrical
Columbia District Office (803) 791-8800 elopez@edtengineers.com
Education: – B.S. Electrical Engineering (2003), University of Puerto Rico at Mayagüez
Employment History: 2001: Summer, Professional in Training, Puerto Rico Electric Power Authority PREPA 2003-2008: Resident Engineer, Luis M. Carrillo, PSC 2008-2009: Supervisor Engineer, Puerto Rico Electric Power Authority 2009: Project Director, Luis M. Carrillo, PSC 2010-2014: Project Engineer, Eng. Miguel A. Bonilla, PSC 2014-2015: Manager of Engineering, Environmental Control, Building Maintenance and Power Systems, Claro (America Movíl) 2015-Present: Consulting Engineer, Engineering Design & Testing Corp.
Experience: Electrical construction, maintenance and operation; electrical failure analysis; code, permits and standards evaluation; facilities maintenance; power systems operation and maintenance; environmental regulations compliance; operation of control systems for waste water treatment facilities; personnel supervision; construction management; fire origin and cause investigations; damage assessment and repair/replacement analysis; evaluation of power generation and distribution systems; litigation support.
Registration: Registered Professional Engineer: • Georgia • Florida • Puerto Rico • South Carolina
Certifications: Certified Fire and Explosion Investigator (CFEI), National Association of Fire Investigators
Professional Organizations: National Council of Examiners for Engineering and Surveying (NCEES)
Engineering Design & Testing Corp. is an association of engineers committed to the study, interpretation and resolution of loss.
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