Section I: Principals of Electricity

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Section I Principals of Electricity
Statistics Ohms Law Alternating vs. Direct
Current Effects on the Human Body Lab Safety
Manual
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Yearly Statistics in the US involving Electrical
Accidents 200,000 - Accidents
150,000 -
Fires
700 - Deaths

Electrical Accidents are the third
leading cause of industrial deaths in the US
(NIOSH Alert, December, 1986, Publication Number
87-103.) This course covers electrical safety
involving household level voltages (240 and
below), and is not intended to cover power line
applications. Overhead lines are not insulated
and carry between 7,200 and 500,000 volts. Never
allow a conductor to touch an overhead power line
(aluminum ladder, CB antenna, tent pole, backhoe
shovel, TV antenna etc.)
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Ohms Law of Electricity
Voltage is almost always a constant so electrical
current levels are determined by the resistance
to flow. When there is a potential for
electrical shock we can protect ourselves by
maximizing our resistance to current flow. This
is done by wearing insulating shoes and gloves,
and by not making direct contact with a source of
ground potential such as plumbing or other
sources of ground.
V I R V electrical potential (volts) I
electrical current (amps) R resistance (ohms)
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Our skin provides us with a natural barrier or
resistance of approximately 1,000 to 100,000 ohms
depending on several factors including skin
thickness and surface moisture.
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Alternating current or AC is what comes out of
wall outlets. In the United States the direction
of flow of AC changes at a rate of 60 cycles/sec
(hertz). Direct current or DC flows in one
direction. Properties Shocks involving AC tend
to push the recipient away while shocks involving
DC tend to grab hold of the recipient making it
difficult for them to get away from the shock
source.
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Effects of Electrical Shock on the Human
Body Direct Current Alternating
Men Women Men Women Perception
Threshold 5.2 3.5 1.1 0.7 Painful Shock
0.5 62 41 9.0 6.0 Painful Shock
99.5 90 60 23 15 Ventricular
Fibrillation 500 500 675 675 All Units are in
milliamps Reference Introduction to Safety in
the Chemical Laboratory, N. T. Freeman, J.
Whitehead, Academic Press, New York, 1982, pg. 41.
Lower levels of AC than DC will produce painful
shocks in humans while lower levels of DC than AC
can lead to fibrillation of the heart muscle.
Women are more sensitive to the effects of both
AC and DC than are men.
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The University of Georgias policies governing
electrical safety can be found in the Laboratory
Safety Manual (http//www.esd.uga.edu) in Section
2.X, and additional locations.
Section Contents
2.X Power cords, extension cords, surge
protectors 2.I.2.f Bonding and grounding
of flammable liquid containers 2.IV.E Spark
sources and flammable materials 2.VIII.B Explosio
n proof refrigerators for flammable material
storage Appendix J-21 Explosion proof
refrigerators for flammable material storage
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Section II Common Electrical Problems
Extension Cords and Power Strips Power
Cords Solvents and Electricity Water and
Electricity Laboratory Equipment Capacitors and
Transformers
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Power Strips
Power strips are approved for use only with
computers and computerized equipment. They must
be UL 1449 rated (surge suppressed). Power
strips should be used sparingly. Care must be
taken not to overload power strips.
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Extension Cord Hazards
Extension cords are approved for temporary use
only. If extended use is required, hard wiring
such as a new outlet should be installed.
Extension cords are easily frayed, a condition
which may expose bare wires. If not properly
placed, extension cords may also become a trip
hazard.
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Common Power Cord Problems
Exposed Wires
Power cords are doubly insulated and should be
replaced if the outer layer of insulation becomes
frayed exposing wires.
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Short circuit
Shorts cause a great increase in the flow of
current through the cord producing heat and
perhaps initiating a fire. Overloads occur when
more current flows through a cord than it is
rated to handle. Power strips can be overloaded
if too many high current draw devices are plugged
in at one time.
Short
Normal
Plug
V IR As
resistance decreases, current increases.
Overloaded circuit
Outlet or Power Strip
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Common laboratory equipment such as centrifuges
and ovens are high current draw devices. If two
or more high current draw devices are plugged
into the same outlet or power strip an overloaded
circuit may result.
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Overloaded Circuit
Another common way in which power cords can be
overloaded is by plugging one power strip into
another. All of the current drawn by any device
plugged into any of the strips must flow through
a single cord
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Care must be taken to insure that power cords do
not come in contact with hot surfaces such as the
top of a hot plate where they may melt exposing
bare wires. Frayed or melted cords should be
replaced immediately before bare wires are
exposed.
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Solvents and Electricity
Common household refrigerators employed in
laboratories must have a LABORATORY USE ONLY
sticker. Household refrigerators should never be
used for the storage of flammable liquids due to
the many spark sources that are present.
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The NFPA (National Fire Protection Association)
diamond provides a quick visual indication of the
hazardous properties of a substance. A rating a
rating of 3 or 4 indicates a severe hazard.
Flammable liquids (NFPA flammability rating of 3
or 4) that require refrigeration must be kept in
either an explosion proof or a flammable storage
refrigerator.
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Explosion proof and flammable storage
refrigerators are specially designed for
flammable liquid storage. The interior of these
two types of refrigerators do not contain any
potential spark sources such as lights and
switches.
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Flammable solvents must never be heated with an
open flame or other potential ignition source.
When solvent heating is required, mantles or
other spark free sources must be employed.
Mantle heaters must be plugged into a control
device such as the Variac pictured in the lower
right hand corner of the illustration. Mantles
must never be plugged directly into a wall outlet.
Mantle Heater
Variac
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Variacs and other spark sources such as power
strips must be located outside of any fume hood
where flammable vapors are present.
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Bonding Strap
Grounding Strap
Dispensing Container greater than 5 gallons
 
 
Earth Ground
When dispensing flammable liquids from containers
larger than 5 gallons, the containers must be
bonded and grounded to prevent build up of static
electricity. Bonding is achieved by making a
conducting connection between both containers
using grounding straps or thick copper wire.
Grounding is achieved by making a conducting
connection between the larger vessel from which
liquids are dispensed, and earth ground. When
non metal containers are employed, bonding and
grounding is performed by making direct contact
with the liquid.
 
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Many plastics such as those found in truck bed
liners readily hold static charge. Explosions
can occur when gas cans are placed on a bed liner
before they are filled. The build up of static
electricity is most likely to be a problem on
cold dry days.
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Water and Electricity
Outlet without GFCI
Eyewashes should be located away from electrical
devices and outlets. Outlets within six feet of
a sink or other source of plumbing must be GFCI
protected in order to minimize shock hazards. An
unprotected outlet (non-GFCI) is illustrated
above.
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Safety showers must not be located directly over
switches, outlets, equipment, or other sources of
electrical energy such as those shown in the
picture to the left.
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Oil immersion baths are often employed to control
the temperature of a reaction. The wire coil
that comprises the heating element must be hard
wired (soldered to a plug and insulated). Oil
immersion baths should never be connected to a
source of electrical power by the use of banana
clips or other temporary connections.
Exposed Wiring
Oil immersion bath
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Power supplies represent a potentially lethal
source of electrical energy. Exposed connectors
such as banana clips (alligator clips) should
never be attached to a power supply or any other
high voltage, high current producing device.
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Cable Connectors
BNC connectors are used with standard (household)
very low voltage devices such as cable TV boxes.
BNC connectors should never be used for high
voltage applications. MHV connectors are often
used to connect equipment to high voltage sources
such as power supplies. MHVs have recessed
signal leads or feed-throughs, and have
additional shielding at the end of the connector
BNC
Signal lead or feed-through
Additional shielding
Recessed lead
MHV
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Capacitors are located inside of all laboratory
equipment. They come in many different shapes
and sizes. Capacitors can remain energized and
produce harmful shocks long after a piece of
equipment has been unplugged.
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A discharge delivering 10 joules of energy can be
lethal. Ten joules of energy can be delivered by
the discharge of even small highly energized
capacitors (0.2 microfarads charged to 10 KV
etc.). Capacitance (mF) 0.2 20 80 320 3000 Charg
e (KV) 10 1 0.5 0.25 0.1 Note that 320
microfarad (and larger) capacitors can deliver
lethal shocks when charged to household voltage
levels (250 V).
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Capacitors may also contain PCBs or
polychlorinated biphenyls. Capacitors which
contain PCBs must be disposed of properly in
accordance with regulations governing PCBs.
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Typical Transformer
Transformers are potential sources of high
voltage and may also contain polychlorinated
biphenyls.
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Electrophoretic equipment containing high voltage
power supplies and signal leads are found in many
laboratories. Care must be taken to use only
approved equipment. Electrophoretic set-ups
should never be homemade or modified. Leads
should be checked periodically for frays.
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Section III Working Safely with
Electricity
Grounds and Wires Circuit Testers Surge
Suppressors and GFCIs Lock Out/Tag Out Safety
Rules First Aid Fire Fighting
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Three types of Ground Connections
Three types of ground connections are commonly
found. Virtual (also know as floating) grounds
are not true grounds and may be energized. If a
connection is made from an energized virtual
ground to either an equipment or an earth ground,
current will flow (shock potential).
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Outlet Wire Color Conventions
Several different outlet wiring color conventions
exist, but dont take anything for granted. It is
always best to check rather than to assume that a
wire is hot or neutral based upon the wire color.
Typically the hot wire is black, the neutral or
return wire is white, and the ground wire is
green.
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Light Configuration Condition
Open (unconnected) ground Open neutral
Open hot
Hot and ground reversed
Hot and neutral reversed Correct
wiring
Inexpensive circuit analyzers can be used to
determine if an outlet is wired correctly. Open
ground means that the receptacle is not connected
to earth ground. The term hot and neutral
reversed is also called reversed polarity.
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Connection testers are use to determine if a
circuit is energized. Multimeters are used to
measure the voltage, resistance, or current flow
of a circuit or resistor. Both devices should
only be used by trained personnel.
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Function of a Typical Surge Suppressor
Input wave form Output wave form
Surge suppressors reduce voltage spikes and
transients (surges). All surge suppressors
and/or power strips used on campus must be UL
(Underwriters Laboratories) 1449 rated. Check
the back of your power strip/suppressor for a UL
sticker.
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Function of a Typical GFCI
Load
A GFCI or ground fault circuit interrupter shuts
off the flow of current upon sensing a fault
condition such as an electrical shock. Switches
quickly open in the GFCI device in order to
prevent the shock victim from receiving a lethal
amount of electricity.
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GFCI Use
Any outlet within 6 feet of a sink or other
source of plumbing should be equipped with a
GFCI. Recalling Ohms law, VIR, very low
resistances such as an earth ground (plumbing
etc.) allow for very high levels of current flow.
GFCI device may be located at a circuit breaker
instead of an outlet. This arrangement allows
several outlets to be protected with a single
GFCI device.
Typical GFCI Outlet Receptacles containing a GFCI
are noted by the test and reset buttons, and
should be tested monthly to insure proper
operation.
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Breaker locked in off position
Lock out/Tag out
To insure the safety of repair personnel,
electrical panels and equipment with electrical
panels must be locked out and equipment tagged
out of service before any repairs are performed.
The lock must never be removed from an electrical
panel until repairs have been completed, and only
then by an individual with the appropriate
authority. Repairs must only be performed by
trained professionals.
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Common Lock-out Signage
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Common Tag-out Signage
Locked out and tagged out equipment must be
clearly labeled so that no unauthorized personnel
turn on the power or try to use equipment that is
under repair.
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Rules for Working Safely with Electricity
1. Dont attempt any work that you feel
uncomfortable performing. 2. Wear proper
insulating boots and gloves as necessary. 3. Follo
w Lock-out Tag-out procedures as required. 4. For
higher voltage applications, keep one hand in
your back pocket to keep a circuit from being
completed across your heart. 5. Know the location
of any kill switches and cut off
switches. 6. Before working near capacitors,
allow them to fully discharge. 7. Post emergency
numbers by the telephone. 8. Never touch an
energized person with your bare hands but rather
use a wooden broom or other non-conductor to push
them away from a source of current.
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First Aid for Electrical Shock Victims

• The most common symptom of electrical shock is
  physical shock. Signs of physical shock include
• Cold, clammy skin
• Pale face
• Chilled feeling or patient is physically shaking
• Nausea or vomiting
• Shallow breathing.

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Approved Treatment for Physical Shock Patients

• Keep patient lying down
• Keep airway open
• Elevate patients legs if no bones are broken
• Keep patient warm if conditions are cool or damp
• Give fluids if patient is able to swallow
• Never give alcohol to patient
• REASSURE the patient

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Test tag should be current
Electrical Fires
Dry chemical extinguishers (also know as ABC
extinguishers) are approved for fighting
electrical fires. The label indicates the type
of extinguisher that is present. Electrical fires
should only be fought if the situation is well in
hand. If you feel uncomfortable fighting a fire,
pull the alarm and exit the building.
ABC indicated on label
Small Nozzle
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Pressure Gauge
Type A fire extinguishers use water to put out
fires. They are not approved for use on
electrical fires. Type A extinguishers are
denoted by a pressure gauge at the top of the
unit that indicates whether or not the
extinguisher is fully charged. All type A
extinguishers have been removed from service on
the UGA main campus.
Label indicates type A
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Type B or carbon dioxide (CO2) fire extinguishers
should also not be used to fight electrical fires
due to the possibility of moisture condensing on
electrical circuits. Carbon dioxide
extinguishers are denoted by the large funnel
nozzle.
Funnel Nozzle
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This training was developed by Wes Kolar of the
UGA Environmental Safety Division. Please direct
any questions or comments to ESD at the following
number (706 542-5801), or contact us through our
web site (www.esd.uga.edu).