Electrical Outlets 3 vs. 2 prongs
Within the past 50 or 60 years, residential homes were typically required to have three pronged outlets installed for electrical appliances. But for older homes that haven’t undergone electrical upgrades or renovations, you may find two pronged outlets. So what is the difference? Is one better or safer than the other?
In both the two prong and three prong outlet, there is a larger vertical slot on the left and a slightly smaller vertical slot on the right. The left slot is the Neutral. The Neutral is conventionally wired to the white wire and ultimately terminates in the main circuit breaker panel to a bus bar connected to earth ground. The right slot is the Hot. The Hot is wired to the black wire and ultimately terminates in the main circuit breaker panel to a breaker.
In a three prong outlet, the lower hole in between the two slots is Ground. In modern wiring, the Ground is connected to a bare copper (or sometimes green) conductor that terminates in the main circuit breaker panel also connected to a bus bar connected to earth ground.
So where is Ground in a two prong outlet system? Typically in a two prong outlet system, the wiring was done with metal shielded cable clamped to metal outlet boxes. The metal shielded cable is clamped to the main circuit breaker panel which is itself connected to the earth ground. Then the metal outlet cover screw is sometimes used as earth ground, as it is connected to the chassis of the outlet which is connected to the metal outlet box and therefore ultimately grounded.
Under normal operation, electrical energy is provided to the Hot prong and returns to ground via the Neutral when used to power an electrical device. The Ground plug is connected to external metal components in the device such that if there was ever a short circuit or a fault, electrical energy will return to ground via the Ground. The Ground also removes the buildup of static electricity as a result of electrical operation of the device (i.e. motor, compressor).
In order to use a three prong plugged electrical device on a two pronged outlet system, typically an adapter is used to connect the Ground plug to the outlet screw. But in order for the adapter to work correctly, the Ground on the outlet (the outlet cover screw) needs to be verified.
So will a three prong plug electrical device work if the Ground plug is cut or pulled loose? The answer is yes, but there will be an increased risk of electrocution if there is a short circuit or electrical fault to the outside or case of the device. Furthermore, there may also be an increased risk of fire for higher power, higher amperage devices that specifically warn of an increased risk of fire from not having the required Ground.
So what about two prong plug electrical devices? Two prong plug devices today are supposed to be double insulated such that no single failure can result in exposed electrical voltage. Typically this is done through two layers or reinforced insulation of the device. For two-prong devices, however, there is still a need to use the plug in the right orientation (large blade into large slot, and small blade into small slot) in order to prevent reverse polarization (the switching of Hot and Neutral within the device).
ARCCA has engineers experienced and qualified to handle all your fire investigation needs including cases involving electrical issues.