Hi Chris:
"What if the overlay is a membrane key pad or has embedded LEDs?" Depends on whether the circuits for the keys or LEDs are "Limited Power" as defined in IEC 950, Sub-clause 2.11. The issue is: What parts and circuits require a fire enclosure? The answer to this question is found in IEC 950, Sub-clause 4.4.5.1. Parts and circuits NOT requiring a fire enclosure are in Sub-clause 4.4.5.2, third dashed paragraph. If the parts and circuits are "Limited Power," then the overlay can be plastic material rated HB. If the parts and circuits are NOT "Limited Power," then the overlay must be plastic material rated V-1 or V-0. Hope this helps. Best regards, Rich
