User's Manual

2 Fluke Corporation Concerned about arc-flash and electric shock?
The installation of IR windows, panes or ports
allows a thermographer to inspect live electri-
cal equipment without the removal of protective
covers and the exposure of equipment. An
arc-resistant window, unlike a port or pane,
provides additional protection for the thermog-
rapher in the event of an arc flash resulting
from unexpected component failures or work
on other parts of the system. This substantially
reduces the hazard rating for the inspections
and, in most cases, may allow the thermogra-
pher to work more safely minimizing the need
for excessively bulky and cumbersome protec-
tive clothing.
What is an arc-flash?
An electrical system can be subject to two types
of shorting faults:
•
Bolted faults
•
Arc faults
Bolted faults
A “bolted-fault” is everyone’s idea of a short
circuit: such as energizing the circuit with a
ground set in place. A bolted fault results in a
very high current; it is a low impedance short
because of the solid connection. Bolted faults
behave predictably and so conductors can be
rated to withstand the overcurrent for the time
required for an interrupt device to operate.
Bolted faults rarely result in an explosion.
Older switchgear which holds a “fault-rating”
will usually be rated for its ability to withstand
this high current for a particular time period. A
bolted “fault-rated” piece of equipment will usu-
ally have a BIL (Basic Impulse Level) highlighted
on the casing itself in the form of a fault current
for a set duration. E.g 100 kA for 5 seconds.
Arc faults
The second—and far more destructive—fault is
an arc-fault. This occurs when the insulation,
or more specifically the air separation, between
electrical conductors is no longer sufficient to
withstand their potential difference. This can
occur for many reasons. A dropped tool or any
other conductive element (even rust), introduced
between or near energized components may
compromise the insulating clearances. Often,
incidents occur when a worker mistakenly fails
to ensure that equipment has been properly
de-energized. Incidents can even occur when
a worker is simply removing a cover from a
piece of equipment. A significant proportion
of arc faults occur simply due to some form of
component failure and is not limited to human
interaction alone.
In contrast to the low impedance required for
a bolted fault, an arc-fault is a high impedance
short because the discharge occurs through air.
Figure 1. Demonstration of the power of an Arc Flash.
Photo courtesy of ewbengineering.