From: John Trovato <[email protected]> Subject: Re: telco spacing, listings, etc.
Please refer to the requirements for TNV-1 circuits in the 4th amendment of IEC 950. My understanding is that there are no creepage and clearance requirements for T1 or E1 circuits. In fact, it is plainly stated in CTR 12 and 13 that the E1 circuit used to connect to leased lines are SELV. At one time this was not the case. The most stringent test requirements that I know of are those outlined in the Australian deviations to 950, which require both the dielectric and impulse tests to be applied. Australia used to require supplementary insulation between TNV and SELV, even on E1 circuits, based on 250 volts. That is no longer the case with amendment 4. If anyone has a different view, please correct me because I have always found this to ambiguous. At 07:20 PM 1/27/98 -0500, you wrote: >Dear People, > >Well, I'll be the first to say it - >I must be the dumbest person around. > >After having several very patient souls email me >off-line with suggestions I'm still in a quandary. >That is absolutely no reflection on these good people. > >If my product connects to a dry T1 line, the signals >on the T1 line are 3 volt signals. I have a very >technical report detailing results from the >signal mask. In some cases, the report even specifies >milli-volts. All digital. No analog. > >Someone did mention (off-line) that the US views the >T1 line as SELV with the capability of hitting 150 volts. >So, you go to Table 6, UL-1950 and lo n' behold you get >1.6 mm for Basic. That's (TIP or RING) -> GND and >(TIP or RING) -> the other side of the line isolation >transformer. Imposing SELV Basic insulation requirements >thus causes testing to be done at 1,000 volts (Table 18). > >He went on to say that Europe considers the E1 line >as NOT SELV with the capability of hitting 250 volts. >They impose primary voltage standards. Thus, you go >over to Table 6, EN-60950 and lo n' behold you get 2.5 mm. >BUT, that's only for That's (TIP or RING) -> GND. >Spacing to traces on the other side of the line >isolation transformer are doubled for reinforced >insulation and that is 5.0mm. Imposing primary >voltage requirements thus causes testing to be done >at 3,000 volts (also Table 18). > >Both standards agree of 0.4mm for inner layers. > >Now, standards and requirements for primary and secondary >traces outside of telco? No problem. > >But, I'll be damned if I can get someone to tell me (no insult >intended to anyone - maybe it's my stupidity) the rationalization >to "working voltage" of the T1 or E1 line that gets me some >resolution to Table 6 in either standard. And I'll be damned >again if I can find anything in my UL, FCC or CTR reports >or standards that mention anything close to 150 volts for >domestic stuff or 250 volts for European. > >Didn't mean to offend anyone that has helped so far. >The discussion both on and off line has been an eye opener. >Just very frustrated. I'm trying to define and write up >some agency design criteria for engineering. > >And don't be afraid to email me off-line, either. > >mailto:[email protected] > >Regards, Doug > > >
