Hi Treggers, I have a question regarding safety of customer premise equipment (CE) that is typically owned and installed at the customer side. This may have been raised before in this forum, but it may generate some interests for a lot of design engineers out there to come to term with the safety requirement standards (ie. EN 60950, AS/NZS 3260 and UL1950). These satndards are more or less similar to each other with minor changes to suit specific country.
Enough for introduction and now come to the points. With the current technology of ISDD, ATM, Intranet/Internet Conncetion, many equipments have been developed to take the advantage of these technology, however they are also required to provide the analog port for telephone, fax, modem connection. This is usually acheived by using off-the shelf IC such as SLIC (Subscriber Line Interface Circuit) to provide the voltage, current and ringing signal for these telephones, faxes to function. These equipment is also provided other connections such as RS232, Ethernet. Scenario 1: If the equipment is the PC card, the SLIC is drawing power from PC bus (earthed SELV) with step up DC-DC converter to provide the voltage to drive the SLIC to provide ringing signal (which is usually higher than SELV definitions). This port will be classified as TNV2 for internal building wiring so as the SLIC IC itself as there is no isolation inside the IC. (Discussion clauses is refer to clauses in EN60950) a) Does this POTS port (TNV2 circuit) require to have BASIC INSULATION (creepage and clearance) from earthed SELV (Clause 6.2.1.2 & table 19)? Clause 6.2.1.2 also said that "BASIC INSULATION is not required.....". Is it fair to say that BASIC INSULATION is not required since TNV2 and SELV are both connected to protective earth (PE) as the SELV of PC mother board and any ports on PC is connected to PE. The SLIC is also connected to PE in TNV circuit. b) Test procedure of clause 6.4.2, TNV2 port and (c) of Figure 18 do not apply. Is my intepretation in this scenario is correct. Scenario 2: Same as above, but this TNV ports may be wired outside of the building (ie. inter building connection). What is the requirement that applies here since it is subjected to lightning surge and power cross. Is it same as scenario 1 above but the equipment must pass ITU-T K.20, FCC part 68 lightning surge and power cross testing? Scenario 3: If the equipment is a stand alone equipment using DC Double insulated Power Plug Pack (Output 9-112VDC). In this case, even that the SLIC is drawing power from SELV circuit, SELV is unearthed and there is no protective earth is provided for both SELV and TNV circuit. Is it fair to say that BASIC INSULATION must be provided betweeb TNV and SELV. Any information would be helpful, Thanks, -- Aaron Bui (For general WEB posting: My views are just that and are not that of my employer)
