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
