> -----Original Message----- > From: Dwight Hunnicutt [SMTP:[email protected]] > Sent: Friday, July 10, 1998 2:13 PM > > does not "permanence" also imply a permanent connection, as in a hard > ground stud? > > D > Let's look at that. I've looked through IEC60950/A4 and found no significant difference wrt this from 74/484/CDV. The only thing I found in 74/484/CDV relates to the waiver of Basic Insulation in Subclause 2.3.2, similar to how the notes to Table 19 in IEC60950/A4 work.
Assuming no substantive changes to 74/484/CDV, Subclause 2.3.2 for the 3rd ed of IEC60950, the 3rd dashed paragraph says Pluggable Equipment Type A needs a separate terminal, in addition to, "the main earthing terminal." So this is a lot like the Supplemental Grounding Terminal from UL1459/CSA225. The 4th dashed paragraph says Pluggable Equipment Type B either need the same as Pluggable Equipment Type A or a marking on the equipment and in manuals telling users to disconnect TN connections prior to unplugging. Other than that, Subclause 6.1.1 says, if equipment relies on earthing to protect a TN, instructions need to be provided to maintain earthing integrity. Permanence, in the context of the Standard, is preceded by those all important words, "for example." This does not impose a requirement for "permanence." IMHO, this "example" should be moved to a note, because too many people read it as a requirement when it should not be taken as such. Regards, Peter L. Tarver (that's right, he called me Spud) Nortel [email protected] > Peter Tarver wrote: > > > > Ron, you are correct that 6.4.1 makes testing between a TNV-1 or -3 > circuit > > and an SELV circuit moot, if there is a common earthing connection > between > > them. With regard to determining the reliability of the earthing of the > > TNV-1 or -3 circuit, the method of 2.5.11 would be used, with the test > > current set to 2A. UL, CSA and TUV Rheinland NA have endorsed the 2A > value. > > > > Regards, > > > > Peter L. Tarver, PE > > Senior Regulatory Engineer > > Homologation Engineering > > Nortel, MPK > > ESN 655 > > V: 408-565-2453 > > F: 408-565-2575 > > > > > -----Original Message----- > > > From: [email protected] [SMTP:[email protected]] > > > Sent: Thursday, July 09, 1998 4:57 PM > > > > > > Alan, > > > > > > You stated that: > > > >Paragraph 5 of clause 6.4 of EN60950/A4 which follows items a) b) > > > >and c) states the following: > > > > > > > >'These requirements do not apply where circuit analysis and > > > >equipment investigation indicate that safety is provided by > > > >other means, for example between two circuits each of which > > > >has a permanent connection to earth.' > > > > > > Your reference to 6.4 above should actually be 6.4.1 which > specifically > > > refers > > > to electrical separation (see also Table 19), not the impulse test of > > > 6.4.2.1. > > > However, if a TNV-1 or TNV-3 circuit and an SELV circuit are > permanently > > > connected to earth, then there may be no separation requirements > between > > > them, > > > therefore, no testing should be required, if I'm reading the standard > > > correctly. > > > > > > If an overvoltage fault occurred (such as an impulse of 6.4.2.1 that > you > > > mentioned) between unearthed TNV-1 or TNV-3 circuits or conductive > parts > > > and an > > > SELV circuit (in this case), that fault current must be reliably > routed > > > to > > > earth (see 2.3.3.3). In particular, the "permanence" of the SELV > > > connection to > > > earth is described in 2.5.11, particularly the 2nd to last paragraph. > See > > > also > > > 6.3.2. > > > > > > I hope this answers your questions and that you will be soon out of > your > > > misery. :-) > > > > > > Comments anyone? > > > > > > Best regards, > > > Ron Pickard > > > [email protected] > > > > > -- > > DWIGHT HUNNICUTT > Sr. Compliance Engineer > > **************************** > * <[email protected]> * > * (510) 413-1349 direct * > * (510) 492-0808 fax * > * VINA Technologies,Inc. * > * 42709 Lawrence Place * > * Fremont, CA 94538 * > ****************************
