Transcript Electical Safety Presentation

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Electrical Safety
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Introduction
•Each year, about 9% of the fatalities in
the American workforce is by
electrocution while working around
electricity. Many other workers are
injured.
Note: Based on Bureau of Labor and Statistics
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Electrical Safety
•This course is designed to present safe
electrical work practices. Since
electricity is the most widely used form
of energy in most facilities, it is
imperative that safe work practices are
followed.
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Introduction
• The Federal government, through OSHA, has
set a number of rules and regulations for
working with electricity. These rules are in the
29 CFR 1910.
• Michigan Rules:
 Part 39-Design Safety Standards for Electrical Systems
 Part 40-Electrical Safety-Related Work Practices
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Voltages
•The safety precautions in this
presentation will be used for voltages
between 50 volts and 600 volts. Most
hospital equipment is set up for 115
(120) volts for most plug-in devices.
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The “Code”
•It is important to remember that this is
an overview. The national and local
electric “Code” will take precedence
over any material in this presentation.
•Maintenance will follow the Code.
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Electrical Hazards
•29 CFR 1910.303(b)(1) requires that
”Electrical equipment shall be free from
recognized hazards that are likely to
cause death or serious physical harm to
employees”
•Michigan has adapted the appropriate
OSHA regulations
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Electrocution
•There are many sources of information.
However, the accepted information
states that a level of current between 70
and 200 milliamperes, if passed through
the heart, can cause ventricular
fibrillation. A milliamperes is 1/1000 of
an ampere.
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Ventricular
Fibrillation
Ventricular fibrillation means the heart
loses meaningful pumping action thus
causing death in a short period of time.
This happens when a small current
passes either (a) from head to foot, or
(b) from hand to foot and thru the heart.
About 100 milliamperes can do it
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Electrocution
•A typical household receptacle has about
15 Amperes
•15 Ampere x 1000 = 15,000 milliamperes
•It only takes ~ 100 mA to cause
ventricular fibrillation.
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Voltage
 Voltage: is the amount of electrical force
(electromotive force).
 This is the difference of electron and proton
potential.
 This measurement is between two points.
This can be between “hot” and neutral, or
between other charged items. Voltage is
measured in volts (E).
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VOLTS
RMS
Hot
Neutral VOLTS
One Cycle
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Voltage
120 V
0V
120 V
220 V
100 V
120 V
100 Volts
difference
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Nominal
 Nominal: is the term used for the stated
voltage for a given line. Example a 115
volt circuit may actually be 120 volts,
but is called 115 volts nominal.
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Current
•There are two different types of current:
AC-Alternating current
DC-Direct current
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Current
 Current: is the amount of electricity that
flows in a circuit. Current is measured
in amperes (I) (Amps).
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AC to DC
Rectified
RMS
Even flow of current
12V
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AC and DC
•Most existing equipment run on AC and
DC
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Resistance
 Resistance: opposes (uses) the flow of
current measured in Ohms (R). This is
caused either by the nature of the
material or work done.
 Example: A toaster wires get hot due to
resistance.
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Volts and Amperes
Resistance
Voltage but no amps
Force
Voltage & Current
Given point
Force and movement
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Ground
 Ground: Is the process of achieving
earth neutral. This can be achieved by
strategically placed earth grounds, or
through a combination water main and
earth ground. This ground should
supply the system with a ground wire
and neutral potential.
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Ground
•This is the symbol for ground.
•May be on the back panels of equipment.
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GFCI
•Ground Fault Circuit Interrupter
Prevents electrocution by detecting a
ground fault and opening the circuit up.
Activates at 5 mA 61 mA and 1/25 of a
second fault.
Note:Other sources have indicated between 4-7
mA and 1/40 of a second.
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Ground Fault
A fault between Hot and Ground
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GCFI-Receptacle
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GFCI
•Are used in wet areas
Bathrooms
Kitchens
Outside work
Maintenance
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Overcurrent
•Overcurrent is the extra amount of
current that passes through a circuit and
an overcurrent protection device that
usually opens the circuit.
•These devices are usually circuit
breakers or fuses. The fuses and
breaker are on the load side of the
disconnects.
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Overcurrent Protection
•A fuse or breaker usually works on the
principle that the extra amount of
amperage will cause a conductor to get
hot and either “blow” or move to open
an overloaded circuit.
•You have fuses or breakers in your
house and car.
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Short Circuit
•A short circuit is when there is a direct
contact between “hot” and “neutral”.
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Parallel Circuit
•Even with one open circuit branch, the
system is still hot.
•Don't become
part of this
120 volts
circuit!
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Static Electricity
•Static electricity is the buildup of the
difference of potential between
materials.
Positive

Negative
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Static Electricity
• Static electricity is the buildup of the
difference of potential between materials.
• Static electricity is high in voltage but low in
amperage (in most cases).
• This is why you feel the static release charge,
but usually it does not do physical bodily
damage.
• This spark can ignite flammable vapors and
dust.
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Static
charges
are
caused
by
friction.
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Clearance distance
around panel boxes
Normal voltage
to ground
Clearance distance
0-150
3 feet
151-600
3 ½ feet
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Safety Distance
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Disconnect Identification
3
1
2
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Plugs
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Receptacle
Return neutral side
Hot side
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Extension Cords
• 1910.305(g)(1)(iii) does not allow
flexible cords to be used:





As a substitute for fixed wiring
Running through holes
Running through doorways, windows, etc.
Attached to building surface
Behind walls, ceiling, or floors
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Extension Cords
•Additional material covered in
1910.305(g)(2)(ii-iii) requires that most
flexible cords will not be used with
splices, and will have a stress relief
fitting or device to prevent the cord from
pulling on the terminal screws.
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Temporary wiring:
•1910 305(a)(2) requires that temporary
wiring be used for that purpose and not
take the place of permanent wiring, and
only be in place for a maximum of 90
days for decoration and like items.
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Grounded Equipment
•Never use a plug with a missing ground
prong.
•Always check before plugging into a
receptacle.
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Three Prong Cords
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Three Prong Cords
•Never use a plug with the ground prong
missing.
•Inspect all plugs for missing or bent
blades or prongs.
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End
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