Darrell, Rich What if the overlay is a membrane key pad or has embedded LEDs? Then it is not a decoration. This is my situation How does this change the evaluation?
Regards Chris Wells Sr Des. Eng. Cutler-Hammer ------------- Original Text From: C=US/A=INTERNET/DDA=ID/richn(a)sdd.hp.com, on 4/30/97 6:29 PM: Hi Darrell: 1. Do overlays outside the 94HB enclosure material need a flame rating? The answer depends on which certification house you are submitting your product to. According to the standard, the overlay would be considered a "decorative part." A decorative part is defined as a part, outside the enclosure, which has no safety function. (IEC 950, Sub-clause 1.2.6.5.) According to the standard, decorative parts are required to be 94 HB or better. Except: "Small" decorative parts are exempt from being required to be 94 HB. "Small" is defined by example, nameplates, mounting feet, key caps, knobs and the like. (IEC 950, Sub-clause 4.4.4, third paragraph.) Some certification houses will tend to ignore ANY decorative parts, while other certification houses will negotiate what size or particular decorative part needs to be 94 HB. In practice, MOST plastics are UL-certified and flame-rated. I would be surprised if your overlay was not made of UL- certified and flame-rated material. Furthermore, overlays are usually not critical as to choice of material. So, the easy way out is simply use a UL-certified plastic for your overlay. 2. Double-sided tape, not required for safety or function. (If the tape is not required for function, then why use it? My guess is that the tape is required to hold an insulating sheet in place, and the insulating sheet is required for function; therefore, the tape is required for function.) If the insulating sheet is required for safety, then the tape would perform a safety function of holding the required insulating sheet in place. If this is the case, then the tape would need to be a UL-certified tape rated for the temperature incurred in the product. If the tape is truly functional, then the tape would be treated as a "small part." Specifically, flammability requirements do not apply to thin insulating materials such as adhesive tape used directly on any surface, PROVIDED that the combination of the thin insulating material and the surface comprise 94 V-2. (IEC 950, Sub-clause 4.4.3.3, third dashed paragraph.) 3. Adhesives not relied on for safety. Adhesives are addressed in IEC 950, Sub-clause 4.3.22. This only applies to securing specific safety-related parts. The requirement specifies tests for aging properties. There are no requirements for adhesives for functional purposes. However, UL 1950/CSA 950 address adhesives in Annex P.2, under Sub-clause 4.3.22. Adhesives must comply with the adhesive requirements of UL 746C (the standard which you like!). Be aware that some certification houses will want to evaluate the consequences of failure of the adhesive. That is, if the adhesive should fail, and the part should move around within the product, could it bridge a safety insulation, or short a circuit so as to cause a fire? 4. IEC 950 not helpful on plastics. I invite comments on the "user-friendliness" of IEC 950 and its clones. And for other standards. Which safety standard is "good" in regard of "user-friendliness"? What are those "good" characteristics? What are the characteristics of a "user-friendly" safety standard? Best regards, Rich r