This analysis is a good overview on requirement for connection to an IT power system. Much better than my somewhat glib reply.
In general, I have not demanded that agency-issued certs specify IT power in the conditions of acceptability if the construction documentation and test data clearly indicate conformity to IT power connection requirements. And I have never been concerned that my UL reports specifically stated for connection to a TN power system, as there is no market for IT in North America. But based on Mr Gies's reply, and the marginal quality of recent agency reports, I think that I must insist that the conditions of acceptability for my Class II/2 products state the power systems. I hate it when other people make me think on Fridays... luck, Brian > -----Original Message----- > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf > Of Don Gies > Sent: Thursday, October 11, 2007 4:51 PM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: RE: Class II PSU for IT power systems > > Kris, > > If you have an electronic copy of the standard, do a search > on "IT" and > determine if the clause is applicable. For instance, if you > do so with IEC > 60950-1, 2nd Edition, you will hit on 1.5.8, concerning > components connected > between line and earth. Not applicable. Next is a > installation manual note > in 1.7 as to whether your equipment has been evaluated for > IT systems--hold > the thought there. Then you go to 2.7.4, or overcurrent > protection. The > clause says that you don't have to be concerned about > protection against > earth faults if you do not have an earth connection, and you > only need one > protective device against overcurrent. Next is 3.4.6 concerning > disconnects. The wall plug-in unit is your disconnect. > Next, and possible > most significantly, if your Class II unit had a heater, > 4.3.7 would require > a temperature-sensing device to disconnect both the line and neutral > conductor. I suspect your plug-in unit contains no heaters, > but if it did, > and you only had only one cutout, you can still draw current > through the > unprotected supply lead to earth even after the line > conductor cutout opens > if your impedance to earth is not infinite in the IT > circuit. Lastly, you > go to 5.1.3, or touch current, and since this section does > not exempt Class > II products, you have to consider touch current and the > applicable circuits > in IEC 60990. > > Going through the above, I would say yes, you can consider > IT supplies for > Class II wall-plug in units under IEC 60950-1, but there is > probably no > impact. > > Regards, > > Don Gies, N.C.E > Senior Product Compliance Engineer > Alcatel-Lucent > Murray Hill, NJ 07974-0636 USA > > > -----Original Message----- > From: Carpentier Kristiaan [mailto:kristiaan.carpent...@thomson.net] > Sent: Friday, October 05, 2007 9:59 AM > To: EMC-PSTC@LISTSERV.IEEE.ORG > Subject: Re: Class II PSU for IT power systems > > Brian, > > I am referring to IT power distribution system and a class > II wall plug, > thus w/o a PE pin. > My assumption is that this wall plug does not have to comply with > additional requirements related to IT power distribution > system because > there is no connection to PE. Nevertheless, some CB reports > state that > tests have been done on the wall plug for IT power > distribution system > and some other don't. > > Best regards, > > Kris Carpentier > Regulatory & Approvals > > -----Original Message----- > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org] On Behalf Of Brian > O'Connell > Sent: vrijdag 5 oktober 2007 15:50 > To: emc-p...@ieee.org > Subject: RE: Class II PSU for IT power systems > > If I am not missing something obvious, the construction answers the > question. > > Class II construction does not have to depend on a > protective earth for > protection against shock, so there is no need for the ground pin. > > Perhaps we have a 'terminology disconnect' - are you > referring to an "IT > power distribution system", or perhaps a "Class 2 output" ? > > Note that for connection to an IT power distribution system > (which could > be either isolated or separated by some impendence from any 'system' > earthing), it may not be possible to clearly indicate the earthed > conductor to mains, so there are additional requirements for mains > disconnect. > > I have advised designers, for equipment designed to be > connected to an > IT > power distribution system, to not rely on any ground bonding for > protection against shock. > > Additional note - UL listings will sometimes indicate "IT > Power Source"; > this is NOT referring to an IT power distribution system. > > luck, > Brian > > > -----Original Message----- > > From: emc-p...@ieee.org [mailto:emc-p...@ieee.org]On Behalf Of > > Carpentier Kristiaan > > Sent: Friday, October 05, 2007 2:18 AM > > To: emc-p...@ieee.org > > Subject: Class II PSU for IT power systems > > > > Hi Group, > > > > Does it make sense to test a Class II wall plug PSU for IT > > power systems > > as there is no PE pin on such a PSU? > > Some CB reports mention that testing for IT power systems > is done and > > some don't. > > > > Best regards, > > > > Kris Carpentier > > Regulatory & Approvals - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. Website: http://www.ieee-pses.org/ To post a message to the list, send your e-mail to emc-p...@ieee.org Instructions: http://listserv.ieee.org/request/user-guide.html List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas emcp...@ptcnh.net Mike Cantwell mcantw...@ieee.org For policy questions, send mail to: Jim Bacher: j.bac...@ieee.org David Heald: emc-p...@daveheald.com All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc ______________________________________________________________________ This e-mail has been scanned by MCI Managed Email Content Service, using Skeptic(tm) technology powered by MessageLabs. For more information on MCI's Managed Email Content Service, visit http://www.mci.com. ______________________________________________________________________
