Hi Bob, I believe that you are concerned about overloading the output wiring beyond its ampacity, so that's what my comment below addresses.
Output of 4A at 24Vdc could fall within the guidelines for Class 2 (UL 1310) or Limited Power Source (UL 60950-1) power supplies. If the power supplies you are using are separately certified as Class 2 or LPS, and outputs are not paralleled and run through a single set of wires, then I would guess your certifier may not look any further. Even if this is the case, it would be a good idea to make sure your wiring can carry at least 8A continuously. If this is not the case, then the easy way may be to just test in the end application, as Doug suggested. Also, make sure the input overcurrent protection falls within the guidelines or Conditions of Acceptability of the supplies. On Tue, Dec 23, 2014 at 11:28 AM, Doug Powell <doug...@gmail.com> wrote: > > Sorry all, > > My decimal place was off. Blame it on thumb typing. That should be 84.6 > Watts and for standards like IEC 60950-1 this may indeed meet the 100 VA > limit in Table 2B. > > > > Doug > > > > On Tue, Dec 23, 2014 at 12:08 PM, Doug Powell <doug...@gmail.com> wrote: > >> Bob, >> >> The quickest way to determine the need for output fusing is to do the >> test. That is a short to the output should not result in a hazard such as >> spread of fire, electric shock, ejecting of parts, lifted circuit traces, >> melted insulation, etc. >> >> You use the word small, but 4 x 24= 816 watts. By the reckoning of most >> safety >> standards this is not low energy, meaning you can achieve ignition. >> >> >> Thanks, - doug >> >> Douglas Powell >> http://www.linkedin.com/in/dougp01 >> *From: *Bob LaFrance >> *Sent: *Tuesday, December 23, 2014 11:39 AM >> *To: *EMC-PSTC@LISTSERV.IEEE.ORG >> *Reply To: *Bob LaFrance >> *Subject: *[PSES] fusing outputs of small power supplies >> >> Greetings, >> >> >> >> I am curious to know what guidelines to use when fusing power supplies. >> I have a machine with some small 4amp 24v power supplies. I have placed >> breakers on the input side of supplies. I don’t know if the current limit >> circuits within the power supply can be expected to protect output wiring. >> I am mainly concerned with NFPA 7 & NEC, but I would like to hear UL or IEC >> thoughts on the subject. The power supply manufacturers I have asked don’t >> seem to know – that struck me as very odd. >> >> >> >> Many years ago I worked for a manufacturer of motor drives. We developed >> a software implementation of a motor overload relay and got UL 508 >> blessing. I am looking for similar arrangement. >> >> >> >> Thank you and Merry Christmas. >> >> >> >> >> >> Bob >> >> N9NEO >> >> >> >> >> - >> ---------------------------------------------------------------- >> >> 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 < >> emc-p...@ieee.org> >> >> All emc-pstc postings are archived and searchable on the web at: >> http://www.ieee-pses.org/emc-pstc.html >> >> Attachments are not permitted but the IEEE PSES Online Communities site >> at http://product-compliance.oc.ieee.org/ can be used for graphics (in >> well-used formats), large files, etc. >> >> Website: http://www.ieee-pses.org/ >> Instructions: http://www.ieee-pses.org/list.html (including how to >> unsubscribe) <http://www.ieee-pses.org/list.html> >> List rules: http://www.ieee-pses.org/listrules.html >> >> For help, send mail to the list administrators: >> Scott Douglas <sdoug...@ieee.org> >> Mike Cantwell <mcantw...@ieee.org> >> >> For policy questions, send mail to: >> Jim Bacher <j.bac...@ieee.org> >> David Heald <dhe...@gmail.com> >> >> > > > -- > > Douglas E Powell > > doug...@gmail.com > Skype: doug.powell52 > http://www.linkedin.com/in/dougp01 > - > ---------------------------------------------------------------- > > 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 < > emc-p...@ieee.org> > > All emc-pstc postings are archived and searchable on the web at: > http://www.ieee-pses.org/emc-pstc.html > > Attachments are not permitted but the IEEE PSES Online Communities site at > http://product-compliance.oc.ieee.org/ can be used for graphics (in > well-used formats), large files, etc. > > Website: http://www.ieee-pses.org/ > Instructions: http://www.ieee-pses.org/list.html (including how to > unsubscribe) <http://www.ieee-pses.org/list.html> > List rules: http://www.ieee-pses.org/listrules.html > > For help, send mail to the list administrators: > Scott Douglas <sdoug...@ieee.org> > Mike Cantwell <mcantw...@ieee.org> > > For policy questions, send mail to: > Jim Bacher <j.bac...@ieee.org> > David Heald <dhe...@gmail.com> > -- Scott Aldous Compliance Engineer Google 650-253-1994 scottald...@google.com - ---------------------------------------------------------------- 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 <emc-p...@ieee.org> All emc-pstc postings are archived and searchable on the web at: http://www.ieee-pses.org/emc-pstc.html Attachments are not permitted but the IEEE PSES Online Communities site at http://product-compliance.oc.ieee.org/ can be used for graphics (in well-used formats), large files, etc. Website: http://www.ieee-pses.org/ Instructions: http://www.ieee-pses.org/list.html (including how to unsubscribe) List rules: http://www.ieee-pses.org/listrules.html For help, send mail to the list administrators: Scott Douglas <sdoug...@ieee.org> Mike Cantwell <mcantw...@ieee.org> For policy questions, send mail to: Jim Bacher: <j.bac...@ieee.org> David Heald: <dhe...@gmail.com>
