Transcript Electrical Safety - Qualified Employees

For Qualified Electrical Workers
Electrical Hazards
 SHOCK. Electric shock occurs when
the human body becomes part of the
path through which current flows.
 The direct result can be electrocution.
 The indirect result can be injury
resulting from a fall or movement into
machinery because of a shock
 BURNS. Burns can result when a
person touches electrical wiring or
equipment that is energized.
 ARC-BLAST. Arc-blasts occur from
high- amperage currents arcing
through the air. This can be caused
by accidental contact with energized
components or equipment failure.
 ARC-BLAST. The three primary
hazards associated with an arc-blast
are:
• Thermal radiation.
• Pressure Wave.
• Projectiles.
 EXPLOSIONS. Explosions occur
when electricity provides a source of
ignition for an explosive mixture in
the atmosphere.
 FIRES. Electricity is one of the most
common causes of fires both in the home
and in the workplace. Defective or misused
electrical equipment is a major cause.
EFFECTS ON THE
HUMAN BODY
Factors:
Current and Voltage
Resistance
Path through body
Duration of shock
Effects of AC Electricity
 More than 3 mA- Painful shock- cause
indirect accident
 More than 10 mA- Muscle contraction –
“No Let Go” danger
 More than 30 mA- Lung paralysis, usually
temporary
Effects of AC Electricity
 More than 50 mA- Ventricular fibrillation,
usually fatal
 100 mA to 4 A- Certain ventricular
fibrillation, fatal
 Over 4 A- Heart paralysis, severe burns
Electrical Equipment
Examination of equipment
 Electrical equipment must be free of
recognized hazards that are likely to
cause death or serious physical harm to
employees.
Examination of equipment
Safety of equipment must be determined
using the following considerations:
Suitability for installation and use
Mechanical strength and durability
Electrical insulation
Heating effects under conditions of use
Examination of equipment
Safety of equipment must be determined
using the following considerations:
 Arcing effects
 Classification by type, size, voltage,
current capacity and specific use
 Other factors
Splices
Conductors must be spliced with:
Splicing devices suitable for the use
Brazing, welding or soldering (with a
mechanically and electrically secure joint
before soldering & then soldered)
Splices
All splices and joints and the free ends of
conductors must be covered with an
insulation equivalent to that of the
conductors or with an insulating device
suitable for the purpose.
Marking
Electrical equipment may not be used
unless the manufacturer’s name,
trademark or other identification is on the
equipment.
Other markings must be provided giving
voltage, current, wattage, or other ratings
as necessary.
Markings must be durable enough to
withstand the environment.
Identification
Each disconnecting means must be
legibly marked to indicate its
purpose, unless located and arranged
so that its purpose is evident.
These markings must be durable
enough to withstand their
environment.
600 volts, nominal, or less
Working space about electrical
equipment.
This section refers to a person
qualified to work on electrical
equipment, usually an electrician.
Working clearances
 Except as required or permitted, the
dimension of the working space in front of
live parts (600 volts or less) and likely to
require examination, adjustment, servicing,
or maintenance must be at least three feet.
 The workspace in front of electrical
equipment must not be less than 30 inches
wide.
 Working spaces may not be used for
storage.
600 Volts or less
Guarding of live parts operating at 50 Volts or
more.
The purpose of this requirement is to
protect any person who is in the vicinity of
electrical equipment against accidental
contact, not just electricians.
600 Volts or less
Guarding of live parts.
Guard against accidental contact by:
(A) Location accessible only to qualified
persons
(B) Permanent, substantial partitions or
screens
600 Volts or less
Guarding of live parts.
Guard against accidental contact by:
Location on a suitable elevated balcony or
platform
Elevation of 8 feet or more above the floor or
other working surface
600 Volts or less
Guarding of live parts.
In locations where electrical equipment
would be exposed to physical damage,
enclosures or guardians must be so arranged
and of such strength as to prevent such
damage.
Over 600 Volts
Workspace around equipment.
Sufficient space must be provided and
maintained around electrical equipment to
permit ready and safe operation and
maintenance.
Work Area Illumination
(Over 600 Volts)
 Adequate illumination must be
provided for all working spaces around
electrical equipment.
 The lights and switches must be
arranged so that persons making repairs
or turning on lights wont contact live
ports.
Elevation of unguarded
live parts
 Unguarded live parts above working space
must be maintained at elevations not less
than specified in Table S-3 of the OSHA
Standard.
 The minimum is 8 feet.
Grounded and grounding
conductors
The grounded conductor is an energized
circuit conductor that is connected to
earth through the system ground. It is
commonly referred to as the neutral.
Grounded and grounding
conductors
The equipment grounding conductor is not
an energized conductor under normal
conditions. It is energized only if there
is a leak or fault in the normal current
path and directs current back to the
source.
Grounded and grounding
conductors
The National Electric Code requires that:
The grounded conductor (neutral) be
continuous white or natural gray.
The equipment grounding conductor be
green, green with yellow stripes or bare.
Polarity of connections
No grounded conductor may be
attached to any terminal or lead so
as to reverse designated polarity.
Reversed polarity is a condition when
neutral conductor is incorrectly
connected to the “hot” terminal of a
plug, receptacle or other connector.
Overcurrent protection
600 Volts or less
Conductors and equipment must be protected
from overcurrent conditions.
Fuses and circuit breakers are designed to
disconnect a circuit from its supply source
when a maximum allowable heat is
reached.
Overcurrent devices must be readily accessible
but not located where they will be
exposed to physical damage or in the
vicinity of easily ignitable material.
Grounding Paths
The path to ground from circuits,
equipment, and enclosures must be
permanent and continuous
Grounding Tools
Tools likely to be used in wet and
conductive locations need not be
grounded if supplied through an
isolating transformer with an
ungrounded secondary of not over 50
volts.
Double Insulation
Listed or labeled portable tools and
appliances protected by an approved
system of double insulation, or its
equivalent, need not be grounded.
However, they must be distinctively
marked.
Electrical Tools
Double Insulated
 They work with GFCIs
 Casing must be labeled
 Tool must be inspected
 Extension cord must be three-prong
Wiring methods.
General requirements.
No wiring system of any type shall
be in ducts used to transport dust,
loose stock or flammable vapors, or
used for vapor removal or
ventilation of commercial-type
cooking equipment.
Temporary Wiring
Temporary electrical power and lighting
wiring may be of a class less than would be
required for a permanent installation.
Permitted for 600 volts or less.
During and for remodeling, maintenance
repair, or demolition or similar activities.
Temporary Wiring
Uses permitted for over 600 volts
only during tests, experiments
and emergencies.
Lighting
Lamps for general illumination must
be protected from accidental
contact or breakage.
Protection can be provided by an
elevation of 7 feet or by a suitable
fixture with a guard.
Conductors entering boxes,
cabinets, or fittings.
 Conductors entering boxes,
cabinets, or fittings must be
protected from abrasion.
 Unused openings in cabinets,
boxes, and fittings must be
effectively closed.
Electrical box covers
 All pull boxes, junction boxes, and fittings
must be provided with approved covers.
 Metal covers must be grounded.
 Outlet boxes must have a cover or a
faceplate.
 Outlet box covers with holes for flexible
cords must bushings or smooth, wellrounded surfaces.
Switchboards & Panels
 Panels must be mounted in approved
cabinets or boxes and must be dead
front.
 Others are accessible only to qualified
persons.
Flexible Cords & Cables
Flexible cords & cables.
Allowed uses:
Pendants
Wiring fixtures
Portable lamps or appliances
Elevator cables
Wiring cranes or hoists
Flexible cords & cables.
Allowed uses:
Connect stationary equipment to
facilitate frequent interchange
Prevent transmission of noise or
vibration
For removal for
maintenance/repair
Flexible Cords
Flexible cords and cables must be
protected from accidental
damage.Sharp corners or
projections must be avoided.
Protection must be provided when
passing through doorways or other
pinch points.
Flexible cords & cables.
May not be used:
As a substitute for the fixed wiring of a
structure.
Where run through holes in walls, ceilings
or floors.
Flexible cords & cables.
May not be used:
Where run through doorways, windows, or
similar openings
Where attached to building surfaces
Where concealed behind building walls,
ceilings, or floors.
Flexible cords and cables.
Flexible cords must be used only in
continuous lengths without splice or
tap.
Hard service flex cords, No. 12 or larger,
may be repaired if spliced so that the
splice retains the insulation, outer
sheath properties, and usage
characteristics of the original cord.
Flexible cords and cables.
Flexible cords must be connected to
devices and fittings so that strain
relief is provided which will prevent
pull off from being directly
transmitted to joints or terminal
screws.
Hazardous Locations
Hazardous (classified)
locations.
Equipment, wiring, and installations of
equipment in hazardous (classified)
locations must be intrinsically safe,
approved for the location, or safe for
the location.
Hazardous Locations
Class I locations
 Locations in which flammable gasses
or vapors are or may be present in the
air in quantities sufficient to produce
explosive or ignitable mixtures.
Hazardous Locations
Class I, Division 1
Location in which hazardous
concentrations of flammable gases
or vapors may exist:
(a) Under normal operating conditions
(b) Because of repair or maintenance
operations or leakage
(c) Because of breakdown or faulty
operation
Hazardous Locations
Class I, Division 2
Location in which flammable gases or
vapors are:
(a) Normally confined within closed
containers or systems
(b) Normally kept below hazardous
concentrations by ventilation
(c) Normally kept below hazardous
concentrations by positive-pressure
ventilation (adjacent to Division 1)
Hazardous Locations
Class II Locations
Locations which are hazardous
because of the presence of
combustible dust.
Hazardous Locations
Class II, Division 1
Location where combustible dust may be
present due to:
(a) Normal operations
(b) Mechanical failure or abnormal
operation of machinery or equipment
(c) combustible dust of an electrically
conductive nature may be present.
Hazardous Locations
Class II, Division 2
Location where:
(a) Combustible dust will not
normally be in suspension in
ignitable quantities
(b) Dusts may be in suspension as a
result of an infrequent
malfunction of handling or
processing equipment.
Hazardous Locations
Class III Locations
Locations that are hazardous because
of the presence of easily ignitable
fibers but in which such fibers are
not likely to be in suspension in
the air in quantities sufficient to
produce ignitable mixtures.
Hazardous Locations
Class III, Division 1
Locations in which easily
ignitable fibers or materials
producing combustible flyings
are handled, manufactured or
used.
Hazardous Locations
Class III, Division 2
Location in which easily ignitable
fibers are stored or handled,
except in the process of
manufacture.
Protective Equipment
Protective Equipment
Insulating blankets,matting, covers,
line hose, gloves, and sleeves made
of rubber must meet specified
requirements for manufacture,
marking, electrical properties,
workmanship and finish.
Care and Use
 Electrical protective equipment must be
maintained in a safe, reliable condition.
 Specific requirements for in-service
care and use are required for insulating
blankets, covers, line hose, gloves, and
sleeves made of rubber.
Qualified Employees
Qualified Employee
(Qualified Person)
One knowledgeable in the
construction and operation of the
electric power generation,
transmission, and distribution
equipment involved, along with
the associated hazards.
Qualified Employee
(Qualified Person)
 Must have the training required by the
OSHA Standard
 Must have undergone on-the-job
training and has demonstrated an
ability to perform duties safely under
the direct supervision of a qualified
person.
Electrical Safety for
the Qualified
Employee