Tony - The UL746 series of standards are referenced in CSA/UL60950, Annex P.2. RTI is a material property evaluated in UL746B, Polymeric Materials - Long Term Property Evaluations. IIRC, guidance on the applicability of RTI is given in UL746C, Polymeric Materials - Use in Electrical Equipment Evaluations. Application of a similar requirement by either IEC60950 or EN60950 depends on the existence of equivalent IEC standards, which, while not directly referenced in IEC60950, 3rd ed., Annex Q, are indirectly referenced by 1.5.1.
RTI provides a temperature at which, over the long haul, the material properties (HAI, HWI, etc), in general, are reduced to not less than predefined percentages of "as received" properties. RTI for many materials are gimmes, typically 50C for thermoplastics and higher for thermosets, some molding compounds and may be higher for certain generic resin types. Higher RTIs than the "generic" are tested for, at the request of the manufacturer. Note that there is an RTI parameter "with impact" and "without impact." Thermal stress at 5 deg. C less than "actual" temperature is, at best, inconclusive for this part. UL746C will have alternative methods for occasions when material properties aren't up to snuff in their Recognitions. The ball pressure test doesn't seem called for and may or may not provide confidence of how the part will perform long term (you don't give enough detail on how the polymer is used). In any case, testing at 125C seems excessive. Regards, Peter L. Tarver, PE Product Safety Manager Sanmina Homologation Services [email protected] > -----Original Message----- > From: [email protected] > Sent: Tuesday, October 02, 2001 5:45 AM > > All, > > I am having some fun with a lab over RTI ratings > on plastics. Basically we > have a plastic moulding with a component mounted > directly on it. The RTI > of the plastic is 60C and the component is > getting to around 75C actual. I > have always looked at the flammability of > plastics 5V, V-0, V-1, etc but > never the RTI. Is this a just a UL1950 > requirement or is it in EN60950 as > well. We have done the thermal stress at 70C and > all is OK. They are > suggesting doing the ball pressure test at 125C, > however, I have only used > this for qualifying mains transformer bobbins, etc. > > Regards > > Tony Reynolds > ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: [email protected] Dave Heald [email protected] For policy questions, send mail to: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
