Ground fault interrupt devices

Small equipment and hand tools are run from plug-in-type receptacles. These receptacles should be grounded and, for safety, equipped with ground-fault interrupter devices. Locking-type receptacles should be used for tools or equipment which are subject to extensive movement during use. 

The ground fault interrupt device, on the other hand, is designed for personal protection however, it is not infallible and cannot be depended upon for total personal safety. Also, it is used in conjunction with a circuit breaker and only for a specific type of electrical hazard, which we will see below. To understand the problem, let s examine how circuit breakers and GFI devices work. 

Simple devices such as fuses, circuit breakers, and ground fault interrupters are available to cut off equipment when they overload or short out or an inbalance develops between the input and output current from a device or circuit. More sophisticated devices can also be used to determine a problem, such as a redundant heat detector used to deactivate a circuit serving a still, condenser, or heat bath should the temperature become too high. 

Saliva contains a mixture of ionic substances and can conduct electricity. For this reason, there can be no direct electrical pathway from the ac supply to the patient. Thus use of isolation transformers should be seriously considered, especially when young children are to be measured. An alternative is the use of battery-powered units, which are especially attractive because there cannot be a stray path to ac electrical ground as long as the unit is not hooked to an electrical outlet. Although most hospitals have grounded ac outlets and ground fault interrupters, respiratory medical devices are being used in homes, clinics, and schools where such safety precautions may not be installed. 

Although it is not necessary, it would be a good idea for the instructor of this course to purchase a "ground fault interrupter" (see page 57 and index) in a hardware store, attach a power cord (similar to the item above), and place it and its socket in a plastic "enclosure" box such as Radio Shack Catalog Number 270-1809. Then all 120 volt ac power, even for the soldering iron, can be obtained via this safety device. 

There are two basic types of electrical circuit protection devices fuses and circuit breakers, and ground fault interrupt (GFI) devices. A circuit breaker is more or less like a reusable fuse. Many people are unfamiliar with how electrical safety devices work, even though these devices are found in all homes. We assume that circuit breakers and GFI devices are... 

The voltage developed would thus oscillate around the normal voltage and fall in phase with the fault current to achieve a near-strike free interruption of the interrupting device on a ground fault. 

From this equaiion one can determine the required value of neutral circuit impedance for a particular level of ground fault current. The external impedance will be Z, less the ground impedance. In HT systems one c in also delermine the likely value of a ground inductor coil to achieve a near-resonance condition, to eliminate the arcing grounds, on the one hand, and facilitate a strike-free extinction of an arc hy the interrupting device, on the other. 

GFI, GFCI - Ground fault (circuit) interrupter - a device that senses ground faults and reacts by opening the circuit. 

Safeguards against electrical shock—are static dissipation devices, ground-fault circuit interrupters, and grounding and bonding mechanisms. 

Circuit protection devices, such as fuses, breakers, or fault-interrupters, may be required in case of excessive current draws as a result of a short circuit, overcurrent, or earth fault. Several options exist with circuit breakers preferred over fuses. In some of the newer devices several functions are combined into one, thereby reducing the total number of components. An example of this is a combined power-switch/circuit-breaker. The switch/breaker is used as a switch and breaker and senses each line and opens all lines, except the grounded line, simultaneously when a fault current is present. Also, the switch/breaker looks and functions as a standard power ON/OFF rocker switch. In some standards simultaneous interruption of the phase and neutral is required, thereby, precluding the use of fuses. 

A GFCI can shut off the power supply to a device or bioinstrumentation amplifier within IS to 100 ms of the start of a fault current to ground. This interruption process is so fast that a person may not experience the sensation of a fault shock and even may then wonder why the instrument is not working. 

AFCIs are electrical safety devices designed to automatically stop the flow of electricity in an electrical circuit when the arc fault is detected within the circuit, to prevent fires from developing. Arc faults are considered one of the major causes of residential electrical fires that occur each year in the United States. Since 2008, new homes built in the United States are required to be provided with AFCIs. See also Ground Fault Circuit Interrupter (GFCI) Grounding. 

Ground-fault circuit interrupters (GFCI) used for wet areas Guards or covers in place for electrophoresis devices... 

Ground-fault circuit interrupter. A device for the protection of personnel that functions to deenergize a circuit or portion thereof within an estabiished period of time when a current to ground exceeds some predetermined vaiue that is iess than that required to operate the overcurrent protective device of the suppiy circuit. 

Electrical equipment in process facilities is often exposed to rain and process fluids. Therefore it is important to use Ground Fault Circuit Interrupters (GFCIs) in these situations. These are devices that will trip and disconnect a circuit when the leakage current to ground exceeds approximately 5 mUliamps—below any personnel hazard level. The speed of response generally is less than 0.05 seconds for 15—20 amp units. GFCIs should be used for the following applications ... 

Using voltage-rated rubber gloves or jumpers when removing the water meter or repairing a water service within an excavation Electrical protective devices, including fuses, circuit breakers, and ground-fault circuit interrupters are critically important to electrical safety. Ensure all such devices are... 

As the public supply system employs neutral earthing, the most common method of compliance with this Regulation is to connect together any earth exposed and extraneous conductive parts by means of low impedance protective and bonding conductors. This is the EEBADS technique outlined in Chapter 3. The technique creates an equipotential zone so that when an earth fault occurs these conductive parts are raised to substantially the same potential with respect to the ground (earth). This condition persists until the protective device, be it a fuse or a circuit breaker, interrupts the circuit and clears the fault. Anyone in simultaneous contact with more than one of the conductive parts should not experience a shock because the parts are at about the same potential. 

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