Mr. Varju gave a very good summary of the requirements to Mr. Lee, but I need to clarify that there has been an update to the 12 Megohm max. static discharge resistor requirement. That resistor has been replaced by a high voltage surge test.
The reference is UL Bulletin dated November 9, 1995, under subject 1950. Section 5 of the bulletin reported on the results of the Binational AdHoc group on "ITE with provisions for connections to outdoor antenna and cable systems" (pages 7 through 10 of the bulletin). The conclusion, found on page 10, is that UL now requires a voltage surge test instead of the static discharge resistor. The surge is either per IEC 65 (50 discharges from a 1 nf capacitor charged to 10 KV), or per UL 1492 (4 discharges from a 0.1 uf capacitor charged to 10 KV). The manufacturer has the option of either test. The manufacturer does NOT have the option of using the resistor in lieu of the test, however. The effective date of that requirement was set as "upon publication" (page 3 of the bulletin). Since there were no comments from the industry in the 30 days allocated for response to the bulletin, this translates into the requirements being effective NOW. And by NOW, I mean that the surge test was enforced on my equipment in February of this year. Presently Listed constructions using the static discharge resistor will continue to be Listed and will not have to be subjected to the voltage surge test. to maintain the Listing. An interesting sideline is that this applies to both the Second and the Third edition of UL 1950, meaning that it also applies to the binational Standard (i.e. the Ad Hoc committee was Binational, the Third Edition is Binational, and CSA should also be enforcing this). Gabriel Roy Highes Network Systems Maryland --------------------------------------- snip ------------------------------------------ Mr. Lee: For a multimedia computer, there are two areas that you must address in addition to the considerations of a normal PC. 1. The modem. It must comply with the telecom requirements of Std 950. Also, in Canada, the modem must be approved by Industry Canada. In Europe, it must be approved by each country's telecom regulating body. 2. The TV tuner. Since the tuner may be connected to an external antenna, it can build up a very large static electric charge, and it is also exposed to possible lightning strikes. So a discharge path must be provided. Since Std 950 doesn't address this issue directly, CSA uses Std. No. 1 as a reference (this is the home entertainment - radio/TV standard). This standard requires that you provide a discharge resistor from the antenna to the neutral of the power supply. The exact values escape me right now (I'm at home) but I seem to recall that the resistor must be between 4Mohm and 12Mohm, 1/2W. By the way, UL requirements are almost identical, except that the subject resistor must be UL Recognized. I'm not sure what they are doing about this in Europe, but the applicable standard is IEC 65. Regards, Egon Varju CSA Pacific
