The Basics of Home Electrical Grounding
All circuits should be equipped with a grounding system to minimize the risk of electrical shock.
When the electrical codes were revised in 1962, they mandated that all 120-volt circuits be grounded; when the codes were revised again in 1999, they mandated that all 240-volt circuits be grounded. Grounding is simply making all metal parts of a circuit come in contact with the ground, which reduces their voltage to zero and prevents electrical shock or fire in the case of a malfunctioning electrical system.
Consider the following scenario: a hot wire on a ceiling light fixture that is not connected to a grounded circuit becomes dislodged. It comes in contact with the metal canopy of the fixture. A result of metal’s excellent conductivity is that the entire fixture would get extremely hot.
If you attempted to replace a lightbulb, for example, the electrical current in the fixture would seek to get grounded by using you as a channel to accomplish this goal. The upshot of this would be that you would receive quite an unpleasant surprise. A similar scenario may play out everywhere electricity and metal come into contact.
An electrical grounding diagram
However, none of this would be possible if the circuit was equipped with a grounding system, which is often a wire that connects to the neutral bus bar in the service panel and the metal casing of the light fixture. When the current attempts to complete its circuit by passing through the grounding wire, the fuse or circuit breakers will cut off all current flow, protecting both the circuit and your home from damage.
In most construction projects, nonmetallic sheathed cable (type NM) with a grounding wire is used instead of metallic cable. The unsheathed grounding wire of the NM cable is shown connected to the neutral bus bar in the service panel at one end and a grounding screw in the metal box at the other end in the figure to the right. In the case of a nonmetallic box, the grounding wire would need to be attached to the receptacle.
Instead of utilizing the receptacle illustrated, you might use a ground-fault circuit interrupter (GFCI) receptacle to provide additional protection. When this type of receptacle senses an imbalance in the flow of electricity, it shuts off the circuit quickly (within 1/40 of a second). This makes all the devices hooked up to that receptacle and all the devices “downstream” powerless.
There isn’t a need for ground-fault circuit interrupters (GFCIs) in a home’s entire electrical system. Still, they must be used in areas with wetness, such as bathrooms and kitchens, and in areas like decks and patios, where there is electricity.