It is often necessary to have an opening in the "fire enclosure" to
provide an operator or display panel. However, a PCB (V-1 or 5V or
better) or glass substrate (for LCDs) behind the opening is acceptable
as a continuation of the fire enclosure.
The trim or bezel can then be regarded as a "decorative" part outside
of the fire enclosure, requiring only HB or better flammability rating.
An oversimplified summary of minimum flammability requirements is:
Outside declared fire enclosure nominally HB
less than HB if quite small
Fire enclosure V-1 if
unit is 18kg or under
5V if unit is over 18kg
Inside fire enclosure nominally
V-2
PCB substrates V-1
Very small, or no substitute exempt from V-2,
material for required function no minimum cited
Note that "fire enclosures" can be (1) the external covers, (2) just under
the external covers, e.g. metal cages, (3) distributed within the outer
enclosure as needed, or (4) combinations of 1 thru 3.
No fire enclosure required for secondary circuits supplied by a "limited
power source" complying with 2.11, if components mounted on material
of V-1 or better, and wiring is of PVC, TFE, PTFE, FEP, neoprene or
polymide.
Regards,
George Alspaugh
Lexmark International Inc.
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