If the transformer is a 'certified' component, what are its ratings and conditions of acceptability?
Do the connected circuits in the end-use equipment have a required interrupt rating? What article of the code is being applied? Per admin law, Field assessment only done by a NRTL or AHJ. Any fuse where the melting integral will not cause problems with normal operations would be ok if the overload and s/c tests do not result in excessive winding temperatures. Transformers assessed per UL5085 or CSA No.66 series will indicate requirements for current interrupt component. Brian From: Kunde, Brian [mailto:brian_ku...@lecotc.com] Sent: Monday, October 31, 2016 8:59 AM To: EMC-PSTC@LISTSERV.IEEE.ORG Subject: [PSES] Low current Transformer OC Protection Greeting Experts. I often run into issues with safety inspectors during Field Evaluations regarding overcurrent protection of small transformers that are not thermally protected. These small transformers can draw such small amounts of current on both the primary and secondary, that finding a fuse within 300% (250%) of the primary or 167% of the secondary max load current is impossible. Even if we use the smallest fuse we can find (Littelfuse 218 series is 0.032A), this value can be over 3000% of the load current. Even if we provide thermal test data to an inspector, they will reply that our data is worthless to them as they only accept data from their own lab or other NRTLs. So am I missing something here? The NEC says I can use the next highest common fuse value. Is this acceptable even if the value is exceeds 1000% of the load current? Has anyone ran across this issue with inspectors? How best do we protect small transformers and meet the electric codes? Thanks in advance. The Other Brian ________________________________________ LECO Corporation Notice: This communication may contain confidential information intended for the named recipient(s) only. If you received this by mistake, please destroy it and notify us of the error. Thank you. - ---------------------------------------------------------------- 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> - ---------------------------------------------------------------- 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>
