FEATURE THERMAL IMAGING A QUESTION OF STANDARDS
When specifying an infrared window IRISS explains how can you define the functionality and safety aspects required before attempting to modify an electrical enclosure in any way
ANSI/NFPA 70 where ambient temperatures do not exceed 40°C. UL 746C is a standard to test
performance of polymeric (plastic) components and identifies the ability of a window to withstand impact or flame. UL 1558 is relevant to viewing panes and
Components such as IR windows must be subject to standard industry tests to confirm they meet the mechanical strengths and environment properties for each electrical cabinet or assembly to which they are being fitted
he minimum requirements necessary for certifying a product to UL standards are usually sufficient to ensure the safe and reliable operation of the product - true or false? In the case of an infrared (IR) window
T
this is not necessarily true as specific application details must be factored in before its use can be deemed ‘safe’. UL is a US-based, Nationally Recognised
Testing Laboratory (NRTL) and worldwide safety consulting and certification company that performs safety testing. UL is the only organisation to have a defining standard (UL 50V) for infrared windows. These devices are basically data collection ports for infrared inspection by thermal imaging cameras that are designed to allow electrical inspections to be conducted with the utmost safety when the system is under load. They ensure the electrical enclosure
remains in a ‘safe and guarded condition’ so the risk of arc flash or electrocution injury is eliminated.
CONSIDER THE BIGGER PICTURE Not all infrared windows were created equal. Hence, anyone specifying an IR window needs to dig deeper than the UL 50V standard to be 100% confident in the suitability of the chosen window type. This base line standard simply verifies that the window provides a means for passage of infrared radiation but it carries an important caveat. UL 50V specifically
10 NOVEMBER 2016 | FACTORY EQUIPMENT
states: “meeting the requirements for this standard do not assure the window is suitable for use in any application and that suitability for continued use requires additional evaluation as to the performance characteristics necessary for the installation.” So what other certifications should you
look for when specifying an infrared window? The following provides more detail in defining the functionality and more importantly, the safety aspects required before attempting to modify an electrical enclosure. UL/NEMA 50E are environmental standards which apply to electrical enclosures that are intended to be installed and used in non-hazardous locations. These include enclosures for indoor locations only (NEMA types 1, 2, 5, 12, 12K and 13) and those for both indoor and outdoor locations (NEMA types 3 and 3R). NEMA ratings can be self-certified when the manufacturer has third party tests to support the assigned ratings. More common to Europe are Ingress Protection (IP) ratings that can be mapped to equivalent NEMA enclosure ratings with the fundamental difference that IP ratings must be tested and certified by a third party laboratory. UL 508 requirements cover industrial
control panels intended for general industrial use, operating at 1500V or less. This equipment is intended for installation in ordinary locations in accordance with
IR windows fitted into metal-enclosed, low voltage (<600V) power circuit breaker switchgear assemblies. This standard requires the impact resistance of an assembly to be tested with the window closed; an essential criteria is that is that a 12.7mm diameter rod should not be able to pass through the window or cover. IEEE C.37.20.2 section a.3.6: this standard and test procedure for viewing panes mounted in electrical equipment with ratings above 1kV requires viewing panes to withstand both impact and load tests. Unlike UL this does not give any dispensation for material composition of the IR viewing window or whether or not covers are fitted. This simple test requires that both sides of the IR viewing window be subjected to impact and load and that neither side can crack, shatter or dislodge. For crystal optic based IR windows this is a requirement that is impossible to meet. IEC 62271-200 provides a controlled arc
flash test for 52kV and below on metal- enclosed switch gear. The test is performed at 6kV using a current of 31.5 KA for a duration of 0.5 seconds. The procedure determines the amount of pressure and heat installed components on switchgear can survive and still maintain integrity.
MEETING STANDARD INDUSTRY TESTS It should be noted that an ‘arc tested’ or ‘arc resistant’ rating can only be given to a completed assembly and not a single component within that assembly. Electrical cabinet designs and
dimensions are infinite and we MUST NOT use data from one cabinet design to another unless they are identical in every way. This is why components such as IR windows can never carry a generic arc rating and must be subject to standard industry tests to confirm they meet the mechanical strengths and environment properties for each electrical cabinet or assembly to which they are being fitted.
IRISS T: 01245 399713
www.iriss.com
Page 1 |
Page 2 |
Page 3 |
Page 4 |
Page 5 |
Page 6 |
Page 7 |
Page 8 |
Page 9 |
Page 10 |
Page 11 |
Page 12 |
Page 13 |
Page 14 |
Page 15 |
Page 16 |
Page 17 |
Page 18 |
Page 19 |
Page 20 |
Page 21 |
Page 22 |
Page 23 |
Page 24 |
Page 25 |
Page 26 |
Page 27 |
Page 28 |
Page 29 |
Page 30 |
Page 31 |
Page 32 |
Page 33 |
Page 34 |
Page 35 |
Page 36 |
Page 37 |
Page 38 |
Page 39 |
Page 40 |
Page 41 |
Page 42 |
Page 43 |
Page 44 |
Page 45 |
Page 46 |
Page 47 |
Page 48 |
Page 49 |
Page 50 |
Page 51 |
Page 52
