video Short Circuit

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Transcript video Short Circuit

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What is an arc flash
5 min.
Video arc flash
5 min.
What causes an arc flash
10 min.
Video PPE
15 min.
PPE demo
10 min
Flash hazard
15 min.
***Flash hazard analysis
***Flash protection boundary ______
60 min.
An Arc flash is essentially a bolt of lightning that occurs around
energized electrical equipment. It can occur spontaneously and is
often triggered simply by the movement of air when an electrical
enclosure is opened.
Every person who has worked around energized electrical
equipment is familiar with arc flash – most have seen it first hand.
But it is kind of like a major automobile accident: No one really
expects it to happen to them, so people have a tendency to drive
with significantly less caution than they should.
So it is with arc flash, only worse. Similar to driving, you can make
a mistake, or you can be doing everything right when someone
slams into you.
Specifically, what is an arc flash? An arc flash is electric current
flowing through an arc outside its normal path where air becomes
the conductor of high thermal energy (more than 5,000 degrees
Celsius) and generates highly conductive plasma.
Arc flash will conduct all available energy and generate an
explosive volumetric increase of gases which blows electrical
system doors off and potentially generates shrapnel.
Arc Flash
Accident
- live cam.
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Accidental contact with energized parts
Inadequate short circuit ratings
Tracking across insulation surfaces
Tools dropped on energized parts
Wiring errors
Contamination, such as dust on insulating
surfaces
• Corrosion of equipment parts and contacts
• Improper work procedures
• The vast majority of arc faults occur when the door
is open or being opened.
An arc faults happens when electric current flows through air gaps
between conductors. Insulation failure and accidents caused by
touching a test probe to the wrong surface or slipped tool are the
most common causes of an arcing fault. The fault current
magnetic fields make conductors to separate producing an arc.
In other words, arc flash is caused by uncontrolled conduction of
electrical current from phase to ground, phase to neutral, and/or
phase to phase accompanied by ionization of the surrounding air.
Because of the expansive vaporization of conductive metal, a lineto-line or line-to-ground arcing fault can escalate into a three
phase arcing fault in less than a 1/1000 of a second. The heat
energy and intense light at the point of the arc is called arc flash.
Short circuits and arc faults are extremely dangerous and potentially fatal
to personnel. The product of arc fault current and voltage concentrated in
one place, results in enormous energy released in several forms. Arc fault
generates large amounts of heat that can severely burn human skin and
set clothing on fire. Temperatures at the arc can reach four times the
temperature of the sun's surface.
The high arc temperature vaporizes the conductors in an explosive
change in state from solid to vapor. Copper vapor expands to 67,000
times the volume of solid copper. Conductive vapors help sustain the arc
and the duration of the arc is primarily determined by the time it takes for
over current protective devices to open the circuit. For example, fast
acting fuses may open the circuit in 8 ms or faster while other devices
may take much longer to operate and open. Metal is blasted and
splattered from the fault location. The arcing faults also produce large
shock waves that can blow personnel off their feet. The other exposure
risks to arcing faults include flying debris, severe sound waves, shock
hazard due to touching energized conductors etc.
Arc
Flash
Demo
Note:
1.Electrical equipment and circuit wiring are considered energized
unless placed in an electrically safe work condition such as
locked, tagged, tried, tested and grounded.
2.Standard PPE (i.e. Hard Hat, FRC, Safety Glasses and Safety
Shoes) is required for all electrical work.
3.PPE requirement (i.e. UV face shield) is based on the
assumption that work is performed within the arc-flash boundary.
4.Voltage rated gloves with leather protectors are required for all
energized work / voltage testing.
A dangerous condition associated with the release of energy
caused by an electric arc.
Arc flash incidents involving workers who are not properly
protected results in more than 2000 workers being admitted to
burn centers each year. The best protection from the arc flash
hazard is to establish an electrically safe work condition. If that is
not feasible, the alternative is to conduct a flash hazard analysis
according to a published safety procedure, then wear appropriate
FR clothing.
A study investigating a workers potential exposure to arcflash energy, conducted for the purpose of injury prevention
and the determination of safe work practices and the
appropriate levels of PPE.
An arc occurs when an insulating medium such as air
breached by a conducting component. An arc flash, defined
as the energy released during an arcing fault, occurs when
current flows through a medium that is not intended to
conduct electrical current. Because the arc current is not
intended, the arc current releases energy that also in not
intended, thus exposing a worker to unexpected hazards
A flash hazard analysis must consider the possibility that an
arcing fault might occur. If an arcing fault occurs, workers are
exposed to unexpected conditions. The flash hazard analysis
must determine the degree of the hazards associated with the
unintended conditions.
In an arc flash event, electrical energy is converted to other
forms. The other forms of energy include heat, pressure, IR,
UV, visible light, and energy at other electromagnetic
frequencies. As currently practiced, however, the flash
hazard analysis considers only exposure to thermal energy.
The analysis must determine the amount of thermal energy
to enable a worker to select appropriate PPE.
An approach limit at a distance from exposed live parts
within which a person could receive a second degree burn if
an electrical arc flash were to occur.
The flash protection boundary id the first issue to be defined
in a flash hazard analysis, the Flash Protection Boundary
defines the point at which FR protection is necessary to
avoid a second-degree burn. Any of all body parts of a worker
are required to be protected.
If a workers hand and arm are within the Flash Protection
Boundary, the hand and arm must be protected from the
thermal hazard. If a workers head is within the Flash
Protection Boundary, the workers head must be protected
from the thermal hazard.
A complete Fr clothing and equipment system that covers the
entire body, except for the hands and feet. This includes
pants, jacket, and bee-keeper –type hood fitted with a face
shield.
The personal protective equipment industry has experienced
a dramatic evolution of protective schemes and equipment
for workers. During this time, the term flash suit has not been
used consistently throughout the industry. This definition
clarifies the specific components that comprise a flash suit
and points out that a face shield may not be used when a
flash suit is required.
Both a shock analysis and an arc flash analysis are required before any person is
permitted to approach the exposed live part. There analysis must answer the
following questions:
• Does a shock hazard exist?
• Will the worker be exposed to the shock hazard at any point during the
work task?
• What is the degree of the hazard?
• What protective equipment is necessary to minimize the exposure?
• Does an arc flash hazard exist?
• Will the worker be exposed to a thermal hazard at any point during the
work task
• What is the degree of the arc flash hazard?
• What protective equipment is necessary to minimize exposure to the
thermal hazard?
• Does a co-occupancy hazard exist?
• What measures will be taken to minimize the impact of other work?
• Will other workers be exposed to an electrical hazard because of the
work task?
• Will the worker be exposed to any other electrical hazard while
executing the work task?
• What authorization is necessary to justify executing the work task while
the exposed conductor/s is/are energized?
Qualified workers who are permitted to work on or near
exposed energized conductors of circuit parts must select
and use work practices that provide protection from shock,
arc flash, and other electrical hazards. The work practices
that are used must minimize any potential for injury. For
instance, body position is one factor that a qualified person
should recognize as an element of the analysis that could
reduce exposure to electrical shock or arc flash.
The hazard / risk analysis must determine whether any
conductor will remain energized for the duration of the work
task. The analysis must determine the shock approach
boundaries and the Flash Protection Boundary.