Hi Alex:
> If a product (product + external non-earthed double > insulated power supply) has been approved for Safety > based on the "Double Insulation" method, what would > be the possible Safety, or any other, consequences if: > > 1. It was decided to earth the COM ports on the product > either via an attached PC or straight earth wire? and You didn't say, but usually the product with an external power supply is supplied by low voltage such as SELV. When this is the case, the product is Class III. A Class III product may be interconnected with a earthed (Class I) product via functional earth circuits. Often, under these conditions, the accessible conductive parts of the Class III product become earthed through the functional earth. Likewise, a Class III product may be connected to earth via a functional earth wire, although this would be a separate and independent user installation. Since you can't control the user installation, you cannot rely on this action for product safety. However, a Class III product, by definition, has no safeguards for electric shock, so earthing the product does not provide a safeguard against electric shock. > 2. Change the power supply to an earthed type (3 wires, > LNE) and the DC Gnd connected to this earth? The power supply for a Class III product may be either Class I or Class II. Best regards, Rich 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 [email protected] Instructions: http://listserv.ieee.org/listserv/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: Richard Nute: [email protected] Jim Bacher: [email protected] All emc-pstc postings are archived and searchable on the web at: http://www.ieeecommunities.org/emc-pstc
