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ELECTRICITY
Electricity has
been around since the beginning of time in the forms of lightning and static
electricity. In 600 BC in Greece, it was observed that amber rubbed with wool
would attract light objects such as straw, feathers, and bits of wood. Around
1570, William Gilbert, the man who is credited with coining the word
“electricity,” discovered electrical properties in items other than amber. The
electric light bulb was invented in 1802, and Thomas Edison was the first person
to successfully market an incandescent lamp, in 1879.
With the ever-expanding use of electricity, the need was recognized for a
national standard to regulate electrical installations nationwide. The National
Electrical Code came into being in 1897. Through the National Fire Protection
Association it became NFPA 70 and remains the same today. It is the electrical
standard for the United States and other foreign countries, including Mexico.
The code is not a training manual; rather, it is a uniform standard used by
inspection agencies, designers, insurance companies, and others who are
responsible for electrical installations. The code is a minimum requirement for
safe installations, and parts of the code became Subpart S and Subpart K of
OSHA’s standards.
GROUNDING
When electricity became part of our lives,
whether in the workplace or at home, effective grounding became our means of
protection. Grounding is still a required method of protection from shock in the
event of an electrical fault. This is the separate wire that is run with the
circuit conductors and connected to the non-current-carrying metal parts of
equipment that could become energized because of a fault.
A grounding conductor is also required in cords that are connected to tools,
equipment, and appliances. The only exception is if the tool is supplied through
an isolation transformer with an ungrounded secondary of not over 50 volts or
uses a system of approved double insulation. The grounding conductor gives a
direct path back to the grounding electrode (ground rod, structural steel, etc.)
if a fault occurs.
When the transistor was invented, we entered into a new era. Now, we were faced
with items such as transistor radios, which operated on batteries or regular
household current. In the mid to late 1960s, one could hardly read a newspaper
or watch the evening news without reading or hearing about a kid or kids being
electrocuted. Typically they would be sitting in the bathtub when their radio
(plugged into household current) fell into the tub, and electrocuting them.
Hairstyles were changing during this period, and the hand-held hair dryer became
a part of practically every household. They posed a problem because they were
primarily used in the bathroom, near the lavatory. This presented additional
hazards because the water piping system was grounded, and a fault in the hair
dryer along with someone coming in
contact with the faucets could result in serious electrical shock or
electrocution.
These factors led to introduction of Ground Fault Circuit Interrupters
(GFCIs).
UNDERSTANDING GFCIs
One of the items covered in the National
Electrical Code is Ground Fault Circuit Interrupters, or GFCIs. The GFCI is
probably the most significant life-saving device ever invented for protection
against serious injury or death caused by an electrical shock.
The GFCI is designed for “personal” protection, not for protection of equipment
or the conductors of a circuit. While grounding is required and is a vital part
of the safety of both people and equipment, the grounding conductor has nothing
to do with the operation of GFCIs.
The GFCI senses an imbalance of current between the “hot” and “neutral
conductor.” The GFCI really does not care about the current draw (amps) passing
through, as long as it is within the designed limits of the device. Rather, it
is monitoring the current difference in milliamperes between the hot and
neutral. A milliamp is .001 or 1/1000 th of an ampere. If this difference is at
5 milliamperes, plus or minus 1 milliampere, the device “trips out,” breaking
the circuit.
A handheld hair dryer that is rated at 1,400 watts, 120 volts, will have a
current draw of approximately 11.6 amperes, or 11,600 milliamperes. An
industrial 3/8-inch electric drill will have a current draw of between 4 and 6
amperes, or 4,000 to 6,000 milliamps.
While electricity performs many tasks for us and makes our lives more enjoyable,
it is basically lazy. The lazy part is that it will seek the path of least
resistance to a grounding source. The resistance in a copper wire used as the
grounding conductor is very low and will allow current to flow rather freely. In
the event of an electrical fault in equipment that has a grounding conductor,
the current will flow to ground on the conductor.
EFFECTS OF
ELECTRICITY
The adult body has about 500 Ohms of
resistance. If a person’s body were to become the path to ground, the body would
become a high impedance ground path. There is not enough current flowing through
the body to trip an overcurrent device (a fuse or circuit breaker; the GFCI is
not an overcurrent device.)
In order for an overcurrent device to trip, the current draw (amps) must exceed
the rating of the device. For example, a circuit breaker rated at 20 amperes
will not trip open until the current exceeds the 20 amperes. Using Ohm’s Law, on
a 120 volt circuit with 500 Ohms of resistance, the current level would be 240
milliamperes, or about 1/4 th of an ampere. Even though this seems like a small
about of current, it is quite deadly when passing through the body.
Shock in the range of 6 to 30 milliamps can be very painful, and the person in
contact cannot let go of the circuit. At around 50 milliamps respiratory arrest
is possible, with severe muscular contractions. Ventricular fibrillation starts
around 67 milliamperes of current. This is when the heart basically starts
fluttering and is not pumping blood through the system. If not stabilized, death
is a real possibility.
So you can see that if the GFCI is functioning properly, the current level will
never reach the danger point—because it trips at 5 milliamperes.
TESTING GFCIs
UL 1943 is the standard for testing GFCIs. Each
manufacturer must ensure that its product meets this standard. Included in the
listing and labeling for GFCIs are instructions that they be tested monthly.
Both the National Electrical Code and OSHA’s electrical standards require that
equipment shall be used and installed in accordance with any instruction
included in the listing and labeling. The purpose of this is to ensure as much
as possible that the device is functioning properly.
The test is a very simple procedure where one can press the test button on the
device to ensure that it does trip, breaking the circuit. This test button
creates a difference of 5 milliamperes between the hot and neutral through a
resister built in the device. There are GFCI testers in the marketplace where
you can test the polarity of a receptacle and also trip the GFCI. I have stated
that the grounding conductor has no part to play in the operation of the GFCI,
but using the external tester the grounding conductor must be present because
the tester is using the hot and grounding conductor to trip the device.
ARE YOUR GFCIs
WORKING?
We take for granted that our GFCIs are
providing protection if we can operate a tool, hair dryer, or other item through
them. Yet this is not always the case. While the device will allow current to
flow through it, the monitoring of the current may not be taking place.
Built into the device is a metal oxide varistor (MOV) used as a surge
suppressor. The MOV absorbs the voltage surge and converts it into heat.
Repeated surges can degrade the MOV, still allowing current to flow but not
providing the protection required. Voltage surges such as lightning strikes in
the area can cause a surge, as can utility company switching. In the event a
GFCI trips out, is reset, and power is restored, you should go a step further
and press the test button to insure that the device trips open to stop the
current flow. If the device will not trip open, or if it trips and current
continues to flow, the device is defective and must be replaced.
Some parts of the country are more susceptible to lightning strikes than others.
This is a primary cause of GFCI failures. The International Association of
Electrical Inspectors obtained information from the American Society of Home
Inspectors about its findings in inspecting residences. This survey only covered
parts of the United States, and some of the figures are staggering about the
number of GFCIs that do not operate properly.
In parts of Florida, up to 58 percent of the GFCI circuit breakers were
defective, and 33 percent of the receptacles. Of the states from which
information was obtained, Washington state had the least number of failures. The
survey covered parts of New York, Florida, Texas, California, Washington, and
Illinois. IAEI, ASHI, and the National Electrical Manufacturing Association are
joining forces get data from each state to give a true picture of the failures
throughout the United States.
THE BOTTOM LINE FOR
SAFETY
If you follow just these two steps, whether at
home or at work, you can help ensure that your GFCIs function as life-protecting
devices.
