User's Manual

11 Fluke Corporation Concerned about arc-flash and electric shock?
These confusing effects are increased further
when mesh is used on both sides of a poly-
mer optic. The radiation from the target is not
transmitted in a repeatable manner through
the IR window; instead, the radiation is in
part deflected back into the panel and in part
transmitted through the first mesh, only to be
absorbed by polymer and the remaining energy
deflected again by the outer mesh.
The resulting signal registered by the camera
may allow a thermographer to locate a hotspot
BUT the transmission of the optic cannot be
accounted for and modelled repeatably.
Window “Standards and codes”
An infrared window is first and foremost an
industrial electrical component: electrical design
and testing parameters must be applied.
Within North America, an electrical component
must be recognized by a Nationally Recognized
Testing Laboratory (NRTL) in order for that com-
ponent to be acceptable to OSHA. Underwriters
Laboratories (UL) are probably the most widely
known NRTL although there are others.
UL have standards and codes that apply to
differing electrical components and infrared
windows are no different. Some of the require-
ments are material specific whilst others are
functionality based.
For example, UL746C is a material standard
that must be adhered to if a product destined
for use as part of electrical equipment contains
polymers. If the product has no polymers used
in its construction, then UL746C does not apply.
UL50, by comparison, is a functional test
that is denoted by a type number and is har-
monized to the NEMA environmental test. In
order to obtain a simple UL50 Type 1 (Indoor)
certification, a product must show that it is
manufactured from components that are non-
corrosive. There are no environmental tests such
as hose-down or dust applied to type 1 compo-
nents. If a component is designed for outdoor
equipment, it will have a UL50 Type rating
higher than Type 1. A typical outdoor rating is
Type 3/12. To achieve Type 3/12, a compo-
nent is subjected to a series of vigorous tests
to ensure that the sealing system and general
construction are sufficient to maintain the envi-
ronmental integrity of the component when put
into service outdoors.
It is not possible to derive a North American
(NEMA) type rating from European (IP) rating.
Terms such as “equivalent to IP65” or “self-
certified” are often used by other manufacturers
whose product cannot pass the more stringent
North American environmental testing.
In order to be sure that an IR Window instal-
lation does not lower a panel’s environmental
integrity, the original NEMA classification of the
host equipment must be matched or exceeded
by the NEMA/UL50 Type classification of the
component. Reputable manufacturers will pro-
vide third party certification of the type rating of
the component, to prove due diligence.
Arc-resistant windows
The strength of crystal infrared window optics
has been increased to such an extent that they
can withstand the effects of an arc fault.
With the adoption of NFPA 70E and the
industry’s focus on arc-flash safety, installing a
product that can withstand arc-flash should be
a primary concern for any end-user.
Finally, some arc flash myths
It is important to separate the truth from the
myth:
•
“99.99 % of arc-flash events occur with the
cover removed”.
This statement is untrue: as mentioned earlier,
19 % of failures occur because of compo-
nent failures with equipment during normal
operation.
A simple industry pointer would be the manu-
facture of arc-resistant switchgear. If arc-flash
events only occurred with open covers, there
would be no market for arc-resistant switch-
gear: it is only “arc-resistant” with the covers
closed.
It is imperative that an infrared window prod-
uct is designed to withstand the pressure and
temperature of an arc-fault.