Hello TREGgers, I have a question about UL 1950 heating requirements:
Which line feeding conditions would you recommend for the heating test (clause 5.1) of a PSTN modem or telephone? According to UL 1950, the test conditions for the heating test for this type of equipment should be taken from "the manufacturer's datasheet". One safety laboratory we know use 56.5 V and 400 ohm as test conditions. 56.5 V is OK with us (being one possible line voltage) but we don't agree with the 400 ohm as it seems too harsh to be reflecting Real Life. Or? The lab says this is the "worst case feeding under NORMAL operating conditions" i.e. with a functional PBX. I know 56.5V/400 ohm is specified in Part 68 but do these conditions really exist IRL? According to EIA/TIA 464-B, 800 ohm is a more reasonable value. As curiosity, I can mention that another lab (located in the same continent) don't even go offhook when performing the heating test... Well, for me this is like testing a toaster without putting down the handle. Most modern modem DAA designs will behave like toasters during this test so the analogy is not so farfetched as it seems. Can anyone comment on this? Any information you may have is highly appreciated. Thanks a lot for your help, Roger Magnuson TGC AB, Sweden
