Electrical Projects An appliance contained in a plastic housing and which has no exposed metal parts should not be dangerous to handle from the standpoint of electrical shock. On the other hand, a portable power tool such as an electric drill can be dangerous to handle, especially if the user is standing on a moist surface or touches a grounded object, unless the metal case of the tool is grounded through a three-prong power plug. It is now standard practice to equip hand tools with three-wire cords terminated in three-prong safety plugs. Power is transmitted through two of the prongs and two of the wires. The third prong is connected to ground through the electric outlet and its wire is connected to the metal frame of the tool. When there is no three-slot 115V outlet available, the tool can only be connected to the power line through a two-prong to three-prong adapter. The adapter has a pigtail lead which is supposed to be connected to the screw that secures the outlet faceplate. If the outlet box (and faceplate) are actually rounded, the tool case is grounded, making it safe to use.

However, when the device has a two-prong plug, it may be dangerous to use if it has ail internal ground. Consider the circuitry of a ground checker that can be assembled in a small minibox. It consists of a small 120V lamp, a DPST toggle switch, a three-hole 115V receptacle (Jl), a Fahnstock clip or binding post (J2), and a two-wire power cable equipped with a standard two-prong plug (P).




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October 6, 2008