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VHS English Version Product Number: 1018HEVHS
DVD English Version Product Number: 1018HEDVD

Excellent program that discusses what GFCIs are all about. Explains how they work, and the general safety procedures for protecting against electrical shock.

Excerpt: Insulation and grounding are two recognized means of preventinginjury during electrical equipment operation. Conductor insulation may beprovided by placing non-conductive materials such as plastic around theconductor. Grounding may be achieved through the use of direct connectionthrough a known ground such as metal cold water pipe. The metal housing orenclosure around a motor or the metal box in which the electrical switches,circuit breakers, and controls are placed. These enclosures protect the equipmentfrom dirt or moisture, and prevent accidental contact with exposed wiring.There is, however, a hazard associated with housings and enclosures. Amalfunction within the equipment such as deteriorated insulation may create anelectrical shock hazard. Many metal enclosures are connected to a ground toeliminate the hazard, but if a hot wire contacts a grounded enclosure a groundfault results which normally will trip a circuit breaker or blow a fuse. Metalenclosures and containers are usually grounded by connecting them with a wiregoing to ground. This wire is called an equipment grounding conductor. Mostportable electric tools and appliances are grounded by this means. There is onedisadvantage to grounding, a break in the grounding system may occur withoutthe users knowledge. Insulation may be damaged by hard usage on the job, orsimply by aging. If this damage causes the conductors to become exposed thehazards of shocks, burns, and fire will exist. Double insulation may be used asadditional protection on the live parts of the tool, but double insulation doesnot provide protection against defective cords and plugs, or against heavymoisture conditions.

The use of ground fault circuit interrupter or GFCI is onemethod used to overcome grounding and insulation deficiencies. The GFCI is afast acting circuit breaker which senses small imbalances in the circuit causedby current leakage to the ground, and in a fraction of a second shuts off theelectricity. The GFCI continually matches the amount of current going to anelectrical device against the amount of current returning from the device alongthe electrical path. Whenever the amount going differs from the amountreturning by approximately 5 milliamps the GFCI interrupts the electric powerwithin as a little as 1/40th of a second. The GFCI will not protecta person from line to line contact hazards such as a person holding two hotwires, or a hot and a neutral wire in each hand. It does provide protectionagainst the most common form of electrical shock hazard, the ground fault. Italso provides against fires, overheating, and destruction of insulation onwiring.

With the wide use of portable tools, and the use of flexible cords,connectors, receptacles, and cord and plug connected equipment, hazards arecreated by improper use and maintenance. Flexible cords are more vulnerable todamage than is fixed wiring. Flexible cords must be connected to devices and tofittings so as to prevent tension at joints and at terminal screws. Because acord is exposed these terminals become more vulnerable. Improperly connectedterminals is another common situation. When a cord connector is wet hazardousleakage can occur to the equipment grounding conductor and to humans that pickup that connector if they also provide a path to ground. Such leakage is notlimited to the face of the connector, but also develops at any wet portion ofit. When the leakage current of tools is below one ampere, and the groundingconductor has a low resistance no shock should be perceived. However, shouldthe resistance of the equipment grounding conductor increase, the currentthrough the body also will increase. Therefore, if the resistance of theequipment grounding conductor is significantly greater than 1 ohm, tools witheven small leakages become hazardous. GFCIs can be used successfully to reduceelectrical hazards on construction sites. Tripping of GFCIs or the interruptionof current flow is sometimes caused by wet connectors and tools. It is a goodpractice to limit exposure of connectors and tools to excessive moisture byusing water-tight or sealable connectors.

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