Voltage, VA, and Touch/leakage current limits allowed by IT SELV/Class I construction exceed NEC article 725 limits - and can be dependent on the whims of AHJ/local code.
Voltage, VA, and Touch/leakage current limits allowed by UL1310 for Class 2 source and Class II construction will meet non-wet NEC limits. Of course, our discussion is only hypothetical as the OP did not indicate end-use safety standard and nor operating environment nor national market. Brian > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf Of John > Allen > Sent: Monday, November 16, 2009 11:36 AM > To: 'Brian O'Connell'; 'EMC-PSTC' > Subject: RE: A very basic safety question. > > Brian > > Whilst I think I know what you may be getting at, the fact > is that an output > considered to be SELV ("Safety Extra Low Voltage", after > all) of a correctly > designed and built Class I device which is connected to to a > correctly > designed and grounded (earthed) supply building system will > be safe, unless > two faults (insulation + grounding) develop - otherwise how > can it be called > "SELV"? > > That, for years, has been the accepted case for IT equipment > where - until > the now widespread use of laptops and other equipment with > Class II PSUs - > almost all such equipment was, and is, Class I. Correctly > installed and > used, this type of equipment is deemed adequately safe in terms of > leakage/touch currents in (al?)most all countries to > (al?)most all codes - > otherwise we have all been living under a severe > misconception for those > many years! > > However, I do agree with you that a poorly designed Class I > PSU, and/or one > connected to a supply system with imperfect or non-existant > grounding, is > another matter. Nevertheless, correctly designed Class I > equipment will not > generate leakage/touch currents in excess of the accepted > limits (given that > the "accepted limits" may or may not be themselves > adequately low in some > circumstances, because getting a "belt" from 3.5mA, or even > 0.75mA, of > leakage current is NOT a pleasant experience!) unless it is > deemed to be a > "high leakage current equipment" per 60950 (etc.). > > Therefore, I think you would need to illustrate your > statement with some > credible examples to back it up. > > John Allen > (The UK one!) > > > -----Original Message----- > From: [email protected] [mailto:[email protected]] On Behalf Of Brian > O'Connell > Sent: 16 November 2009 17:20 > To: 'EMC-PSTC' > Subject: RE: A very basic safety question. > > > For most IT and AV stuff, Class III equipment has no requirement for > protection from electric shock. Any power connected to a > Class III device > must be considered safe to contact. > > A power source with Class I construction, with a SELV output will not > necessarily be considered safe to touch (leakage, inherently > limited power, > etc). Local code requirements could also effect power source > requirements. > > Brian > > -----Original Message----- > From: [email protected] [mailto:[email protected]]On Behalf > Of Piotr Galka > Sent: Saturday, November 14, 2009 2:05 AM > To: EMC-PSTC > Subject: A very basic safety question. > > All, > > Consider two power supplies, both AC230V to DC12V: > PS1 - with basic insulation and one of its output terminals > grounded with > protective conductor, PS2 - with double or reinforced insulation and > floating output. > > I understand that PS1 is CLASS I equipment, and PS2 is CLASS > II equipment. > > Now consider the 12V powered device connected to one of > them. Is that device > CLASS III equipment in both cases? > > Best Regards > > Piotr Galka > MicroMade > Poland - This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. To post a message to the list, send your e-mail to <[email protected]> All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc Graphics (in well-used formats), large files, etc. can be posted to that URL. Website: http://www.ieee-pses.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 <[email protected]> Mike Cantwell <[email protected]> For policy questions, send mail to: Jim Bacher: <[email protected]> David Heald: <[email protected]>
