The ground wire is used in an electrical
circuit to allow current to flow back through the ground instead of through a
person and causing electrical shock. For example, if a live electrical
conductor touched the frame or case of an air-conditioning unit and was not
grounded, then whoever touched that air-conditioning unit would become part of
the electrical circuit if he or she provided a ground. In other words, that
person would receive an electrical shock, which could cause bodily harm or even
death. This condition is shown in Figure 1. The ground wire forces the path of
electrical current flow to pass through the electrical device that is used to
protect the circuit, such as a fuse or circuit breaker. The ground wire is identified
by the color green in almost all cases.
If an electrically powered tool require a
ground, it is equipped with a three-prong plug, as shown in Figure 2. On this
type of plug, the semicircular prong is the grounding section of the plug and should
never be cut off or removed. The same goes for extension cords; the grounding
prong should never be removed for convenience. It is important when using a
power tool that requires a ground that the technician makes certain the
receptacle is grounded. Electrical tools or cord with a ground prong that is
altered should be taken out of service until replaced or repaired. A grounding
adapter shown in Figure 3 is a device that permits the connection of a
three-prong plug to a two-prong receptacle. A grounding adapter should not be
used on a power tool with a three-prong plug unless there is a sure ground that
the grounding wire can be attached to. The technician should use caution when
using grounding adapters because in many older structures grounding is not
provided at the receptacle box. Most late-mode power tools are double insulated
and do not require a ground. This type of tool will have a plug with only two
prongs, as shown in Figure 4.
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| Fig 2. |
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| Fig.3 |
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| Fig.4 |
A ground fault circuit interrupter (GFCI) is an electrical device that will open the circuit, preventing current flow to the receptacle when a small electrical leak to ground is detected. Figure 5 shows a GFCI receptacle with an extension cord plugged into it. This type of receptacle is recommended for use with potable electric power tools. GFCIs are also available in the form of circuit breakers, as shown in Figure 6(a). portable GFCI interrupters are available for use where permanent units are not available, such as on job sites. They are designed to help protect the operator from being shocked. Use ground fault circuit interrupters when required by the NEC. There are also circuit breakers available that will interrupt a circuit when an electrical arc is detected, known as arc fault circuit interrupters (AFCI). Figure 6(b) shows an AFCI breaker that is capable of detecting dangerous arcs that are often caused by loose connectors or by damaged or frayed wiring. Electrical arcs may ignite combustible materials and cause structure fires. Dual purpose breakers are also available that act as both a GFCI and an AFCI. GFCI, AFCI, and dual purpose AFCI/GFCI breakers are very similar their appearance.
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| Fig 5 |
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| Fig 6 |