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Engineering DesignNews

Fun Fact Friday: Electrical Arc Flash Analysis

By April 19, 2019No Comments4 min read

One of the services provided by Encorus’s Engineering Design Group is electrical arc flash
analysis. Electrical arc flash analyses are a safety precaution used to prevent explosions
in industrial settings which utilize high electrical voltage. Director of Engineering
Design and Lead Electrical Engineer Tom Gilmartin offers more information on the subject.
According to Gilmartin, “When an energized wire touches another directly, this is known in
engineering as a fault, and commonly referred to as a ‘short’.  When this happens, the flow of
electrical current through the short has only the resistance of the wires from the generator to the
fault to limit its passage.  Generally, this resistance is very low, so the current flowing in the wire
rises very rapidly.  In a large home, the entire house has a maximum current of around 200
amps, although generally a house will never require this full current.  When a fault occurs in a
home, the current can rise as high as 20,000 amps, and in an industrial setting it is not
uncommon to see fault currents of 200,000 amps.  For a point of reference, lightning strikes are
typically around 1 million amps.  This high current can cause the phenomenon known as ‘arc

Arc flash can occur when a very high current flows between two shorted wires.  As the current
rises, high amounts of energy are released at the point of the short, and the wires start to melt.
As the wires melt, the current will jump the gap, which is known as an ‘arcing current’,
commonly referred to as a spark.  The arc is actually made up of super-heated air known as
‘plasma’. The plasma can reach temperatures of 20,000 degrees.  As the arc forms and the
temperatures rise, the metal of the wires begins to vaporize.  If the arc is sustained long
enough, the vaporization of the metal can cause an explosion, which can approach the energy
levels released by blowing up a stick of dynamite!  Because of this, circuit breakers are used to
detect these high currents and open the circuit, which instantly cuts off the energy flow to the
arc before the energy can cause an explosion.

Fortunately, the relatively low voltage of home electricity cannot sustain an arc long enough to
cause such an explosion, so there is no danger of this in a normal home.  In industrial settings,
however, arc flash is definitely possible and engineers and electricians take precautions to
mitigate these risks.  Electric codes give us plenty of guidance for designing circuits to minimize
the chances of arc flash, and electricians are trained to identify circuits where the danger is
high.  In addition, engineers perform arc-flash studies on large electrical systems to find the
areas of high risk, and design in precautions such as special arc-flash detectors or separate
settings for use during maintenance.  With these methods and training, the risk from arc flash
has been greatly diminished in the last decades.  Engineers and electricians are always on the
lookout for new ways to make electrical systems safer for everyone involved, including workers
and homeowners.”

Arc flash analyses are vital to the safety of people and equipment in industrial settings
with high electrical voltages. If you require an electrical arc flash analysis, contact Director of
Engineering Design and Lead Electrical Engineer Tom Gilmartin, PE, PMP, LEED AP at (716)
592-3980 ext. 124 or