How To Diagnose and Correct Wiring Problems in Receptacles
Improper or careless wiring of receptacles, also referred to as outlets, is the most common electrical defect found in a typical home. Improperly wired outlets are a potential shock hazard and can cause electrical equipment to use more electricity and fail prematurely. Most of the electronic devices such as televisions, stereos, VCRs, video game consoles, and computers have a 3-prong plug due to the fact that the internal wiring is looking for power from one direction of the outlet; improper wiring may cause the device to prematurely fail or can even start a fire.
All receptacles should be wired such that the hot or live (black) lead is connected to a specific side of the outlet, and the neutral (white) lead to the other. A switch on an appliance that is plugged into the outlet will open and close on the hot side. This is done so when the switch is off, there will be no voltage inside the device or receptacle. On a typical receptacle, the hot side is the smaller of the two openings and the neutral is the wider of the two. A cord, where it mates to the appliance, will have one of the prongs wider so the hot and neutral sides line up correctly.
Reverse Polarity occurs when the hot (black) and neutral (white) wire connections are reversed. The hot wire must be connected to the brass screw, while the neutral wire is connected to the silver screw. Some older outlets do not have these colored screws, or the prongs are the same width so you should consider upgrading to prevent any problems.
Open Ground receptacles occur when the bare copper grounding wire is not connected to the green screw on the receptacle. It also occurs in older homes originally wired with a 2-wire system such as knob and tube or duplex wiring and where an upgrade has included a 3-prong receptacle. This is an unsafe practice and does not comply with current Electrical Codes that requires the original or replacement outlet be grounded correctly. If grounding does not exist, the outlet must be replaced with a 2-prong (non-grounding) receptacle or with a 3-prong GFCI (ground fault circuit interrupter) receptacle. The 3-prong GFCI receptacle must also be marked with a "No Equipment Ground" label that comes with the GFCI receptacle.
In some installations, the ground (bare copper) wire may have been connected to the metal receptacle box in which case some homeowners use an adapter, called a pigtail, connected to the cover screw of the outlet to achieve ground. This is an unreliable method and is against most Electrical Codes. As per NEC 250.134; 314.4; 404.9 All electrical equipment, metal boxes, cover plates, and plaster rings shall be grounded. It is much safer to upgrade to a 3-prong receptacle with the ground wire connected directly to the receptacle. Even though some devices and small appliances do not use a ground, it is necessary to provide proper grounding in all receptacles.
An Open Neutral receptacle does not have the neutral wire connected to the neutral terminal. Electrical current travels from the hot wire through the load (whatever is plugged in) and back via the neutral wire in a closed system. In open neutral installations, the circuit is completed through the ground wire which is intended to be the secondary path. In older installations, the neutral is shared by the opposing hot leg of the 240-volt service. This results in erratic voltages which could damage electronic equipment and pose a potential shock hazard.
The problem could be a loose or open connection in another outlet or junction box. Troubleshooting can be difficult, you can use this website as a guide to finding an open neutral in your wiring: The Circuit Detective's Diagnostic Tree - http://www.thecircuitdetective.com/treeopen.htm
Use a voltmeter or receptacle tester/analyzer to check the wiring on your receptacle. With a voltmeter, the voltage between the hot (small) prong and the ground (semi-circle) prong should measure about 100-125 volts. There should be no reading between the neutral (wide) prong and the ground prong. If these readings are reversed, the
outlet has reverse polarity. To correct the problem, the receptacle must be removed from its box and wired as follows:
Hot (black) wire connected to the brass screw (or the side with the narrow prong)
Neutral (white) wire connected to the silver screw (or the side with the wider prong)
Ground (bare wire) connected to the green screw
CAUTION: Turn off all power to outlet and verify that there is no voltage to the outlet before attempting to repair any outlet on your own. You may want to hire a qualified electrician.