forwarded for [email protected]... Jim ____________________Forward Header_____________________ Subject: RE: Surge Testing per EN 55024/EN61000-4-5 Author: [email protected] List-Post: [email protected] Date: 3/3/00 12:16 PM
Jim, One other thing to keep in mind, the modem typically will be grounded by a serial or USB cable to the PC and then to earth through the PC power cord. I believe Surge tests to ground must be performed to determine if any real failure mechanism exists. Keep in mind that events like Lightning are Common mode in nature . Regards, Wolf "Lacey,Scott" <[email protected]> on 03/02/2000 08:51:23 AM Please respond to "Lacey,Scott" <[email protected]> Sent by: "Lacey,Scott" <[email protected]> To: "'Jim Hulbert'" <[email protected]> cc: "'emc-pstc @ieee.org'" <[email protected]> (Wolfgang Josenhans/MW/US/3Com) Subject: RE: Surge Testing per EN 55024/EN61000-4-5 Jim, You do in fact have a potential ground connection - at the phone line. In the static (on-hook) state you will have -48 Vdc, referenced to earth. If you look at your home phone service you will see a wire running to a cold water pipe, with a tag that says something like "Telephone Company Ground - Do Not Remove". PBX systems at work will be different. I have little knowledge of whether they ground or not. I have learned the hard way to look for these non-obvious ground connections. Best wishes, Scott Lacey -----Original Message----- From: Jim Hulbert [SMTP:[email protected]] Sent: Thursday, March 02, 2000 8:52 AM To: Lacey,Scott; [email protected] Subject: RE: Surge Testing per EN 55024/EN61000-4-5 Scott, The product I'm currently looking at uses a 2 -prong AC mains plug. Actually the supply is small direct plug-in type with DC leads that connect to the product. The product itself is encased in plastic and the only other connection is through an internal modem board to a standard analog telephone line. The connection to the phone line is a simple 2-wire (tip and ring) configuration. As I see it, surge tests with reference to earth ground are pointless. Others have pointed out that an "ungrounded" product may in the real world actually have a reference to ground depending on how it is installed or what other equipment it is connected to. That is a good point which I hadn't thought about. However, I don't think that in my particular situation that's that case. Thanks to all who responded with their opinions. Jim "Lacey,Scott" <[email protected]> on 03/01/2000 01:31:46 PM Please respond to "Lacey,Scott" <[email protected]> To: "'Jim Hulbert'" <[email protected]> cc: "'[email protected]'" <[email protected]> (bcc: Jim Hulbert/MSD/US/PBI) Subject: RE: Surge Testing per EN 55024/EN61000-4-5 Jim, I'm not quite sure from the description what your product looks like, but, here are a few things to keep in mind. If you use a 3-prong ac mains plug you absolutely should do the line-to-ground test. If you use a 2-prong ac mains plug you still might want to perform the test anyway, depending on how your product is used. For example, if your plastic housing may be DIN rail mounted or screwed to a wall, you may have a leakage or arc path to earth. Your customer may have deliberately grounded the DIN rail to satisfy the requirements of other vendor's equipment already mounted. Even if it only gets screwed to a plasterboard wall, it still may get grounded by accident. I have seen two such scenarios over the years. In the first instance one mounting screw went through the wallboard and touched the grounded sheath of a BX cable in an older building. In the second instance a screw penetrated a metal stud used to frame the wall. An outlet box was attached to another stud. Bingo - instant ground. I'm sure there are many who will disagree with me, but we test products not only to conform to a standard, but also to ensure a more robust product. I want to find any vulnerability first, before the product gets to a customer. Customers tend to get VERY angry when their new product "hiccups", and the nasty stuff tends to flow downhill real fast when their CEO calls yours. Scott Lacey -----Original Message----- From: Jim Hulbert [SMTP:[email protected]] Sent: Wednesday, March 01, 2000 10:32 AM To: [email protected] Subject: Surge Testing per EN 55024/EN61000-4-5 Colleagues, EN 55024 calls for surge pulses to be applied line-to-line and line-to-earth on the AC mains port and line-to-ground on signal and telecommunications ports that connect directly to outdoor cables. However, if my EUT is encased in plastic covers and has no direct earth ground connection (class 2 power supply), is the line-to-line test on the AC mains the only surge test that I need to apply? It seems to me that performing a line-to-earth test on either the AC mains port or on signal/telecommunications ports is not warranted since the basic standard EN 61000-4-5 does not specify placing the EUT over a reference ground plane. With no reference ground plane and no direct ground connection how can a test be applied with respect to ground? Jim Hulbert Pitney Bowes ------------------------------------------- This message is from the IEEE EMC Society Product Safety Technical Committee emc-pstc discussion list. To cancel your subscription, send mail to: [email protected] with the single line: unsubscribe emc-pstc For help, send mail to the list administrators: Jim Bacher: [email protected] Michael Garretson: [email protected] For policy questions, send mail to: Richard Nute: [email protected]
