Transcript Document
Electrical Safety
Introduction
Electricity is essential to modern life
Some employees work with electricity
directly
Some indirectly
Electricity is a serious workplace hazard
Electricity can be productive and safe
Agenda
Vocabulary
Misconceptions and myths about
electricity
Electrical shock and other injuries
Electrical hazards
Electrical safety for maintenance and
custodial employees
Electrical safety for offices and classrooms
Vocabulary
Voltage
Low voltage
High voltage
Current
Resistance
Conductor
Insulator
Ohm’s law
Voltage
Electromotive force
Electrical potential energy
– “Pressure”
Measured in volts (V)
Low Voltage
Electrical installations and electrical
equipment operating or intended to operate
on systems of 600 volts, nominal,
or less.
All work performed directly on or
in proximity to such electrical installations,
equipment, or systems.
High Voltage
Electrical installations and electrical
equipment operating or intended to operate
on systems of more than 600 volts.
All work performed directly on or
in proximity to such electrical installations,
equipment, or systems.
Beyond the scope of this training.
Current
The continuous movement of electrons
past a given point
Measured in amperes (amps) (A)
– Sometimes the symbol “I” is used
Resistance
Opposition to the movement of electrons
Resistance is used for direct current
Measured in ohms (Ω)
“Impedance” is the proper term for
alternating current
– “Resistance” is commonly used
Conductor
A person who collects tickets
on trains
A person who leads a orchestra,
band, or choir
Conductor
A substance or thing that allows
electricity (or heat) to flow by
passing energy from particle to particle
Silver, copper, gold, aluminum
Insulator
A barrier that wraps conductive materials
to protective against electric shock
A material with little or no
conductive properties
– High resistance
Glass, rubber, mica, and some plastics
Ohm’s Law
R =V/A
One volt will cause a current of one
ampere to flow through a conductor having
the resistance of one ohm
V=A* R
Ohm’s Law
V
(Volts)
A
(Amps)
R
(Ohms)
Electrical Misconceptions
Electricity tends to go to ground
– After it reaches ground, it disappears
Ground serves as just one of
the electrical loops that misdirected
current can use to get back to
the grounded power source
Misconception #2
If an electrical appliance or tool
falls into a sink or tub of water,
the item will short and trip
the circuit breaker
This may not happen because the
sink or tub may be non-conductive
and therefore not part of the
loop to ground
Misconception #3
AC reverse polarity is not hazardous
Many tools have switches in only
one of the two conductors serving
the item
The switch is supposed to be
on the “hot” conductor supplying
he power
Myths About Electricity
Electricity takes the path of
least resistance
Current will take any conductive paths,
high or low resistance, in order to return
to the source that provides it power
Small amounts of current will flow
through paths of high resistance
Myth #2
Double insulated power tools are doubly
safe and will always provide safety
Double insulated power tools can be
hazardous if dropped into water
Electrical current can flow out of the
power tool into the water
Myth #3
It takes high voltage to kill;
120 volts AC is not dangerous
Current is the culprit that kills
Voltage is a factor in determining
how much current will flow
Electrical Shock
A sudden and accidental stimulation of the
body’s nervous system by an electrical
current
Current will flow through the body
when it becomes part of an electrical
circuit
Electrical Shock Dynamics
Current
3+ mA
10+ mA
30+ mA
50+ mA
100+ mA
200+ mA
1500+ mA
Effect
Shock
Muscular contractions
Respiratory paralysis
Heart paralysis (can be fatal)
Ventricular fibrillation (usually fatal)
Heart clamps tight
Tissue and organs burn
Other Injuries
Burns
Falls
Injuries when machinery starts suddenly
Electrical Burns
Current passing through tissue generates
extreme heat
Skin damage at entry and exit
Internal tissue damage
Result from arcs or flashes
Thermal burns from overheated wires or
equipment or fires
Falls
Initiated by a shock
Muscles contract involuntarily
Worker can lose balance and fall
Machinery Injuries
Unexpected activation
Shock
Pinch
Crush
Shear
Electrical Hazards
Bare conductors
Insulation failure
Equipment failure
Static electricity
Heating and overheating
Electrical explosions
Bare Conductors
Live overhead wires most common
Working on rooftops
Repair of electrical systems
Capacitors
Insulation Failure
Heat and elevated temperatures
Moisture and humidity
Mechanical damage
Rodents, fungi
Chemical
incompatibility
Equipment Failure
Older portable tools
Energized housing
Broken connections
Wrongly replaced internal wiring
Lack of grounding plug
Static Electricity
Occurs when two different materials
contact and then separate
High voltage, low current
Flammable liquids
Lightning
Heating and Overheating
Use of electricity results in heat
Can cause accidental fires
Burns out equipment
– Equipment failure and ignition
Hot surfaces
Electrical Explosions
Rapid overheating from overcurrents
Caused by short circuits, power surges, or
lightning
Heated contaminants in oil-filled
breakers or transformers
Capacitors subject to wrong polarity
Safety for Maintenance and
Custodial Employees
Qualified electrical workers
Engineered protection
Safety considerations
Safe practices
Lockout/tagout
Personal protective
equipment (PPE)
Qualified Electrical Workers
A person, designated by the district,
who by reason of experience or
instruction has demonstrated
familiarity with the operation
to be performed and the
hazards involved
Engineered Protection
Insulation
Grounding
Circuit breakers
Fuses
Ground-fault circuit interrupters
Insulation
Parts of electrical equipment coated with a
low-conductive material
Rubber mats to stand on
Rubber gloves
Insulated shoes
Grounding
Protects from shock
Safeguards against fire
Protects against damage to electrical
equipment
System Grounding
One conductor of the circuit is
intentionally connected to earth
Protects against high voltage contact
Stabilizes voltage in a system
Equipment Grounding
Equipment grounded by a permanent and
continuous connection or bond
Provides a path for dangerous fault current
to return to system ground
Enables protective devices to operate
Circuit Breakers
Guard against overloads of current
Ensure current flow does not produce
heat that causes temperature to rise
to dangerous levels
Break the current path
Thermal
Magnetic
Fuses
Guard against overloads of current
Ensure current flow does not produce
heat that causes temperature to rise
to dangerous levels
Break the current path
Melt when current exceeds a designated
value
Ground-Fault Circuit
Interrupters
Fast-acting electrical device sensitive to
very low levels of current imbalance
due to flow to ground
Reduces duration of a shock
Not an overcurrent device like a circuit
breaker or fuse
Types of GFCI
Circuit-breaker type
Receptacle type
Permanently mounted type
Portable type
Cord connected type
Circuit-Breaker Type
A direct replacement for a standard circuit
breaker
Installed in a panelboard
Includes the functions of a standard circuit
breaker
Can protect an entire branch circuit with
multiple outlets
Receptacle Type
A direct replacement for a standard
receptacle
Protects one or more receptacle outlets
Protects additional non-GFCI type
receptacles connected “down stream”
Very popular because of low cost
Permanently Mounted Type
Mounted in an enclosure
Designed to be permanently wired to the
supply
Frequently used around large commercial
swimming pools or similar wet areas
Portable Type
Designed to plug into existing non-GFCI
protected outlets
Contain one or more receptacle outlets
protected by the GFCI module
Easily transported from one location to
another
Approved for outdoor use
– Some are listed as rainproof
Cord Connected Type
Consists of an attachment plug which
incorporates the GFCI module
Protects the cord and any equipment
attached to the cord
Plug has non-standard appearance and is
equipped with test and reset buttons
Safety Considerations
Plan every job
Consider what could go wrong
Use proper tools
– Procedures, drawings and related documents
Isolate equipment from energy sources
Identify hazards that may be present
Safety Considerations
Isolate hazards
Test every circuit, every conductor, every
time before touching
Use PPE, when necessary
Do you have the skills, knowledge, tools,
and experience to perform this work
safely?
Safe Practices
Qualified and authorized electrical
technician
Voltages and frequency should be
identified so that proper precautions can
be implemented
Ratings of overcurrent protection chould
be checked to determine adequate
protection
Safe Practices
Work on de-energized systems
– Use buddy system for energized systems
Never touch a bare conductor until a
system has been de-energized and verified
Enclose and lock all exposed conductors
All removed grounding cables should be
replaced as soon as possible
Safe Practices
Cords should be inspected before using
Repair or replace if defective
All tools, equipment, and extension cords
should be grounded
Use nonconductive tape measures near
energized equipment
Safe Practices
Avoid working on electrical circuits or
equipment while clothing and/or shoes are
wet
Wet floor areas should be covered by dry
wood or rubber matting
Remove rings, watches, keys, and other
metal items before beginning work
Safe Practices
Plug power equipment into wall
receptacles with power switches in the off
position
Unplug equipment by grasping the plug
Check receptacles for missing
or damaged parts
Personal Protective Equipment
Insulating gloves
Insulating blankets
Insulating sleeves
Floor covering
Safety helmets
Safety in Offices and
Classrooms
Outlets
Cords
Machinery
Outlets
Do not overload outlets by using extension
devices to increase the number of outlets at
that socket
Cords
Keep cables, cords, and plugs clean and in
good repair
Protect cords that cross aisles and
walkways
Extension cords are for temporary use only
Extension cords must be 16 gauge
or larger
Extension Cords
Extension cords should not:
–
–
–
–
Be affixed to structures
Extend through walls, ceilings, and/or floors
Be placed under doors or floor coverings
Be subjected to physical or environmental
damage
Multi-Outlet Strips
Multi-outlet strips and surge protectors are
not considered extension cords
One multi-outlet strip should not be
plugged into another
Machinery
Report damaged or defective equipment
– Request repair or replacement
Unplug defective equipment
Carry equipment by the base
– Never by the cord
Do not touch grounded metal parts
Summary
Work environments depend on electricity
Electrical hazards are in all environments
Electrical safety requires effort