In new or recently rewired homes, the electrical outlet receptacles will have three slots instead of two. The third slot is a ground connection used in conjunction with the three-prong plugs found on most modern appliances. It is a safety feature used for grounding the casing of electrical appliances and equipment. If an internal short develops between the wiring and the equipment or appliance casing, the ground connection will direct the current harmlessly to the ground.
For new homes built after 2008, a house electrical inspection should include checking to see if the outlet receptacles are tamper resistant. If the letters “TR” are marked on the face of the receptacle, they are tamper resistant. The National Electrical Code (NEC) mandated in 2008 the use of tamper resistant receptacles in new or renovated construction.
Tamper resistant receptacles have a shutter mechanism that will, in most instances, block access to the electrical contacts from anything but the electrical plug. It is an important safety feature, however not all municipalities have adopted the new code. If you are not sure whether your municipality has adopted it or not, check with your local Building Department.
Some electrical appliances and equipment do not have a grounding wire. In some cases, they are made with double-insulated plastic cases that prevent the user from touching anything electrically charged, even if an internal short would develop. Such equipment does not require a ground connection, therefore it can be used with the older two-slot receptacles as well.
The two-slot receptacles can be used for the grounding of appliances with three-prong plugs via an adapter, typically available at any hardware and electrical supply stores. To complete the ground connection when using the adapter, secure the small wire (pigtail) to the center screw on the receptacle cover plate.
The receptacles, whether two- or three-slot, should be checked to determine if they are electrically hot, whether the receptacles have reverse polarity and whether they are properly grounded. You can do this by using a simple plug-in tester available at any electrical supply store.
Reverse polarity indicates that the hot and neutral wires are connected to the wrong terminals in the receptacle. The switch on an appliance should disconnect the hot wire, keeping everything beyond the switch inside the appliance from being electrically hot when the switch is off.
In the case of reverse polarity, the switch disconnects the neutral wire so that everything beyond the switch will be hot, which could cause an electrical shock. The receptacles in the bathroom and kitchen are of utmost importance and you should make sure they have ground-fault circuit protection. Receptacles that are not properly protected for ground faults are potential safety hazards and the condition should be recorded on your worksheet.