Receptacles that have only a hot and neutral slot are called polarized receptacles. By having a smaller hot wire slot and a larger neutral slot on a polarized receptacle, the electrical current flows the appropriate way through the circuit. For safe use of these receptacles, double-insulated power tools can be used in polarized receptacle circuits. These safety features can reduce the risk of electrical shock, but once again, my advice is to replace the receptacle and rewire if needed to convert the circuit into a properly grounded circuit and receptacle.
And while we’re on the subject of grounding, I’m often asked if using a receptacle adapter is OK. First of all, I’m not a fan of doing something half way. I’d rather change the receptacle to a grounded receptacle and have the ground wire connected to the receptacle and the box. Although you can use an adapter and connect the center cover-plate screw to the adapter to gain a ground if the box is grounded, it just seems like a skimpy, lazy way to fix the real problem, the need for a new receptacle.
Polarized receptacles became widely used in home in the 1920’s and were used in ungrounded systems until the 1940’s. That’s when armored cable, sometimes called Greenfield or BX cable, came along. It is a pair of insulated conductors, a black and white set of wires, wrapped in a metal sheath that provides a ground path. The short circuit or overload is drawn through the metal sheath back to the service panel. The more efficient addition on the 1940’s is the invention of metal conduit. It supplies a great path to ground through the use of metal fittings that connect to boxes and the electrical panel. To add even more grounding security, a ground wire can be pulled inside the conduit to be attached to both devices and the box that houses it.
So, the question is still asked, “Are polarized receptacles safe?” I’d like to pose this question to you, “Which type of receptacle do you feel is safer and which one would you want in your home?” You can use them if you want, but I feel the investment in purchasing grounded outlets far outweighs the cost of replacing them. If you become safety conscious, you’ll see the benefit of updating your home’s electrical devices as they need updating and this may include the electrical service panel as well.