I read in !emc-pstc that Andrew Wood <andrew.w...@landinst.com> wrote (in <e49d8b319a2fd5119e2808002bc33c591c8...@landuk1.landinst.com>) about 'CLASS 11(DOUBLE INSULATED) & 2/3-CORE CABLE', on Mon, 5 Nov 2001: > >All >I have a piece of equipment falling under the scope of EN6010.
Is that a typo or do you really think that is the number? > To set the scene >it is a low volume product, approx 0.5m cube, stainless steel enclosure and >will >sit on a bench in food cold storage areas. Mains lead connects via IP68 >connector. >It incorporates a SMPS for universal mains operation ( current draw approx >0.3A). > >Because of problems ensuring a reliable earth in some locations for its >predecessor, I have specifically designed it to be Class2 (double insulated). >Therefore safe for all markets. > >Now, ironically, I am encountering some "unease" with the UK sales dept. After >all everyone KNOWS that a metal box should be earthed. (I don't dismiss this >attitude lightly because it is no doubt shared by some of the customer base.) >Technically there is no problem with providing a 3-core cable and connecting >up >the earth conductor. And after all if 2 levels of protection is good, 3 levels >is better. > >Option 1 is obviously to stick with the design as is and educate >sales/customers >where necessary. If you provide the product with a moulded-on mains plug, they'll never know it's Class 2 unless they read the rating label! Are you sure that the capacitance between the internals and the metal case is low enough for there to be no detectable 'touch current' if someone touches earth with one hand and your box with the other? Such a detectable current is not hazardous but is extremely aversive - people won't like working with the product if it 'bites', even gently. Assume that all the internals are at half mains voltage to true earth, i.e. 115 V in UK. Now you need to get the touch current down to 0.5 mA at most, preferably 0.3 mA. 115 V and 0.3 mA means 8.3 nF maximum capacitance. Possible, with care. Will your SMPS meet the conducted emission limits with no earth connection? > >Option 2 is to provide a 3core product for the some markets and a 2core >product >for others. This goes against the original intention to have a universal >product. Yes. not convenient at all. > >Is there an option 3? ie provide 3core cable and explain in the manual that >product is designed to be safe without an earth but the earth may be fitted if >desired. What about the square in square symbol? If you provide a 3-core cable, you MUST NOT refer to the product as 'Class 2' or put the double-square symbol on it. But you can explain in the instructions book, if you want to. > -- Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk Eat mink and be dreary! ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. Visit our web site at: http://www.ewh.ieee.org/soc/emcs/pstc/ To cancel your subscription, send mail to: majord...@ieee.org with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Michael Garretson: pstc_ad...@garretson.org Dave Heald davehe...@mediaone.net For policy questions, send mail to: Richard Nute: ri...@ieee.org Jim Bacher: j.bac...@ieee.org All emc-pstc postings are archived and searchable on the web at: No longer online until our new server is brought online and the old messages are imported into the new server.
