Rick, I think you may be right when it comes to non-detachable power cords (hard wired into unit, no IEC Inlet). We always use the IEC Inlet so it can go to different countries so have not had to get a product through safety testing with a non-detachable cord. Here is what UL 1950 section 2.5.9 says:
Protective earthing terminals for fixed supply conductors or for Non-Detachable Power Supply Cords shall comply with the requirements of 3.3. 3.3 Screws and nuts which clamp external power supply conductors shall have a thread conforming with ISO 261 or ISO 262, or a thread comparable in pitch and mechanical strength. The screws and nuts shall not serve to fix any other component, except that they are permitted also to clamp internal conductors provided that the internal conductors are so arranged that they are unlikely to be displaced when fitting the supply conductors. This last sentence does appear to indicate that it should be on top of the stack. Any thoughts from anyone else out there? Kurt Andrews Compliance Engineer Tracewell Systems, Inc. 567 Enterprise Dr. Westerville, OH 43081 Ph. 614-846-6175 Fax 614-846-7791 Email: [email protected] -----Original Message----- From: [email protected] [SMTP:[email protected]] Sent: Tuesday, January 18, 2000 11:01 AM To: [email protected] Subject: RE: Proper Protective Earth Ground Symbol I agree with Kurt's summary of the ground marking and stack-up requirements, but there is a point of clarification I would like to have. Years past, it was explained to me that an appliance inlet ground must be first on the stack-up against the chassis. The point was to ensure that any maintenance action did not compromise the grounding of the enclosure. In the case of a power cord, the opposite was true however. Since a power cord is by definition frequently replaceable (hence the specific requirements for strain relief's and terminal blocks) the ground wire must now be on top of the stack-up. This facilitates easy replacement without jeopardizing the ground. What is the consensus on this? Rick Busche Evans & Sutherland [email protected] -----Original Message----- From: Andrews, Kurt [mailto:[email protected]] Sent: Tuesday, January 18, 2000 8:26 AM To: [email protected]; Jackson; William; '[email protected]' Subject: RE: Proper Protective Earth Ground Symbol Jim, For the Protective Earth Terminal, that is the ground from the power cord or IEC Inlet that should be located just inside the equipment needs to be IEC 417, No. 5019, the circle upside down tree. Also the incoming ground MUST be the first on a stud and secured by its own lockwasher and nut. You may then stack other grounds to other parts of the equipment on top of this ground. You may use a separate lockwasher and nut for each additional ground or one for all of the additional grounds. There may also be other ground studs in the unit if you don't want to run wires to the Protective Earth Terminal. This assumes an all metal construction, which is what we use. We have used both the upside down tree symbol, IEC 417 No. 5017, and the Equipotentiality symbol, IEC 417 No. 5021 for these additional grounds with no problems. For an additional ground on the outside of the equipment we have used the same symbol as for the Protective Earth Terminal. When we sent a unit in once for safety testing to UL we had the upside down tree without the circle next to an outside ground terminal and they told us it has to be the one with the circle around it. I would think that the frame ground symbol, IEC 417 No. 5020 (pitchfork) would also be acceptable although we haven't used it. Hope this helps, Kurt Andrews Compliance Engineer Tracewell Systems, Inc. 567 Enterprise Dr. Westerville, OH 43081 Ph. 614-846-6175 Fax 614-846-7791 Email: [email protected] --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators). --------- This message is coming from the emc-pstc discussion list. To cancel your subscription, send mail to [email protected] with the single line: "unsubscribe emc-pstc" (without the quotes). For help, send mail to [email protected], [email protected], [email protected], or [email protected] (the list administrators).
