Electrical Projects Except in newly constructed buildings, ac outlets are usually of the conventional nonpolarized type which do not provide secure grounding of the appliance. Polarized three-hole outlets are being installed in many new buildings so they will accommodate either the standard two-prong plug or the three-prong polarized plug. It is easy to replace a conventional two-hole ac outlet with a three-hole polarized outlet. The procedure for installing a polarized outlet is as follows: The black wire is connected to the gold screw terminal of the outlet and the white wire to the silver screw terminal. The ground terminal of the outlet should be connected to the green wire (if there is one) or through a short wire to the outlet box. Sometimes, the original installer has run a separate ground wire to the outlet which can be connected to the ground terminal of the new outlet. If the wires to the box have not been run through conduit or armored cable, the box may not be grounded. In that case, the box should be grounded to a cold-water pipe or other nearby ground.

To determine if the box is grounded, without having to remove it from the wall, use a neon test lamp as follows. First, push the test leads of the neon lamp into the two vertical slots of the outlet. This will indicate the presence of ac voltage if the lamp glows. Then, push one test prong into the round grounding hole (above the vertical slots) and the other test probe into the left-side vertical slot. If the box is grounded, the lamp should glow. If the lamp does not glow then but does glow when one test probe is plugged into the round hole and the other into the right-side vertical slot, the outlet is incorrectly wired.




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October 13, 2008