Designating a product as a Class I, Class II, or Class III is not a requirement in any safety standard that I know of.
We safety professionals use the Class designations to evaluate the safeguards in the product. We fool ourselves by designating the Class, and, often, by ignoring other Class construction within the product. I prefer not designating the product class, but designating where the Class I and Class II construction exists within the product. For a moment, consider the common "brick" power supply used with laptops and other computer peripherals. Most are insulation encased. Some have a mains cord with a PE (protective earth). In today's SMPS, there is no grounded barrier in the transformer, so Class I construction is not used in the transformer as a barrier between the mains and the SELV output. Instead, the construction between mains and SELV is Class II. So, what is the PE used for? In most "brick" power supplies, the PE is used to connect the system FE (functional earth) to earth. (Often, one pole of the d.c. output is connected to FE.) If the "brick" employs Y1 EMI capacitors, the earthed side if the capacitors is FE. Is the "brick" a Class I or Class II product? If the "brick" employs Y2 EMI capacitors, the earthed side if the capacitors is PE. Is the "brick" a Class I or Class II product? If the d.c. FE passes the high-current test, but not the constructional requirements, is the FE a PE and is the product a Class I product? The argument as to the Class designation of a product is futile and not useful (and unending with no conclusion). Best regards, Rich - ---------------------------------------------------------------- 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>
