Electrical Grounding Systems and Ground Wires

How Electrical Ground Systems and Ground Wires Work

Normally an electrical ground system and its associated ground wires do nothing. Under normal circumstances no current should flow through them.

However, in the event that a circuit failure does occur, where electricity is somehow directed from the current carrying wires to the metal surface, such as the metal on a light fixture, the electrical ground system works to protect you from electrocution and fire. The electrical ground, in conjunction with the circuit breaker back at the main circuit panel, will instantly cause the circuit breaker to trip, or shut off, stopping the flow of electricity to the circuit and thus preventing the risk of electrocution and fire.

If an electrical ground system was not connected properly to the metal light chassis, and a circuit failure condition occurred, the metal light chassis could potentially be sitting at a 120 volt potential. When someone touched the metal light chassis they could provide a path to ground (ground fault condition), thus causing electricity to flow through them resulting in electrocution. Likewise, if a piece of clothing or some other object was draped over the metal light fixture in this failure condition, current could begin to flow from the metal light fixture, through the object and to Earth ground. The object could heat up and actually catch on fire as a result. Thus an electrical ground circuit, established via the ground wire in an electrical cable plays an important role in protecting your life and property.

What is the Risk of an Electrical Circuit Failure?

It is higher than you might think. If you look into an electrical outlet box, or a light fixture you will frequently see wires tied together with wire nuts. Occasionally wires springs free from wire nuts, or become untwisted. When this situation occurs a “hot” wire could wind up sending current directly onto the metal electrical box or metal light fixture. When this happens you have a circuit failure condition and an electrocution / fire hazard.

Creating Electrical Ground Circuits

Creating an electrical ground circuit is easy to do with today’s home electrical wiring cable technology. Non Metallic (NM) sheathing cable, a.k.a. Romex cable, which is predominately used in home construction today, consists of “hot” and “return” wires as well as a bare copper wire. The bare copper wire should be attached to every piece of metal that the sheathing flows through or comes in contact with, e.g. metal electrical box fixtures, light fixtures, and other electrical appliances. The process of connecting the bare copper wire to the metal surfaces is referred to as “Bonding”. Bonding should be done using green wire nuts, copper crimps, or other techniques that meet national and local electrical codes.

It is also important to never tie, or connect, ground wires and neutral wires together, except at the main circuit panel on the electrical ground / neutral bus bar. The neutral wire is a normal “return” wire for the current flowing through the circuit. By tying the neutral and ground wires together in a circuit, e.g. in an electrical box, you have effectively enabled current to flow through both the neutral and ground wire, which defeats the purpose of the electrical ground system.

The electrical ground / neutral bus bar are connected to an earth ground that normally consists of a very heavy gauge copper wire that is attached to a metal grounding stake that is sunk into the Earth several feet.

Metallic Sheathing Cable Besides NM sheathing cable, there is also metallic sheathing cable that is used in both residential and commercial wiring. Metallic sheathing cable offers the advantage of having the sheathing act as the electrical ground wire itself. However, metallic sheathing cable is more difficult to pull through framing studs, and thus less frequently used today in residential wiring. GFCI Breakers / Receptacles In additional to electrical grounding systems and ground wires, today’s national and local electrical codes also call for the use of Ground Fault Interrupt Circuits (GFCIs) breakers and receptacles to be used in parts of a home that are in close proximity to water, e.g. kitchens, bathrooms, garages and basements.

GFCI breakers and receptacles can measure the inflow versus outflow of current, and when they sense the slightest change between the two, can cause the circuit to be interrupted and immediately stop the flow of electricity, thus preventing the risk of fatal electrocution.

So when working on a home electrical wiring project, do not neglect the bare ground wire. It plays an important role in your home’s electrical wiring system by protecting both you and your home from dangerous hazards.