Home Electrical Grounding Systems are Designed to Protect your Life and Home
By Mark J. Donovan
When performing any type of home
electrical wiring it is extremely important to properly connect the ground
wires to all metal surfaces that the electrical circuit could potentially
come in contact with. Ground wires play an extremely important role in
protecting your life and property from electrocution and fire. As a matter
of fact, the national electrical code requires that all 120 volt and 240
volt circuits be electrically grounded to Earth ground.
The proper electrical grounding
process consists of making sure that every metal part in a circuit, or piece
of metal that could accidentally become part of a circuit, be properly wired
to Earth ground. The reason for this is that that Earth ground is at zero
potential, or zero voltage.
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.
Photo By Mark Donovan
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.
Photo By Mark Donovan
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.
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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.
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