Charles,
Just another data point that might help you. Back in the late 80's, we had an issue with fax machines where the line interface was too often blown and returned for service in the areas with considerable lightning (Alps and neighborhood). Initial testing revealed they would fail at 500V of 10/700 surge, and I thought aaahhhaa - so I fixed it to meet 2 kV. Expecting problem to go away, I found out after a while that the rate of returned blown units stayed about the same. Then we redesigned the input to meet 4 kV and that did it. No more returned units (at least not in any number that would cause attention). Neven -------------- Original message -------------- From: "Grasso, Charles" <[email protected]> Mike - Thanks!! Great reply! _____ From: Mike Hopkins [mailto:[email protected]] Sent: Thu 4/27/2006 7:19 PM To: Joe Randolph; Grasso, Charles; [email protected] Subject: RE: Surge testing limits - research question Back in the 80's, GE and some others did experiments which consisted of forcing 10kA (8/20us waveform) into an isolated household wiring set-up consisting of some number of standard outlet boxes, a distribution panel, some light sockets and switches. The result was voltages that were limited to about 6kV by arcing in the outlets and switches. This is where the 6kV number comes >from in the ANSI/IEEE documents. It is VERY VERY unlikely you would see 10kV inside a building or residence anywhere except at the service entrance itself.... An interesting point is that when using hospital grade sockets and switches, the voltages could get higher...... Another point to remember is that the peak voltages in C62.41 are considered to be an extreme --- I don't have the document in front of me, but I do remember there is a graph in the document that shows that almost anywhere can see 1kV surges, but 6kV is very rare indeed..... Other ANSI standards do call for 10kV testing, but this is strictly for the outside world --- watt meters on the side of a building, submerged pumps, etc.... Once outside the structure, voltages can go to wherever they can during a lightning strike ----- Likewise, 5kV on a telecom line is also extremely unlikely since most of the connectors and cable used won't allow it to happen..... connectors will flash over at well below 5kV in most cases..... Another intersting point is that in most installations today, it's impossible to find surge voltages of any significance ---- I look around my office and home and there are ac protectors everywhere --- mostly MOV's.... On the telecom line, there are protectors in multiple places -- the telephone sets themselves and the telephone switch gear in the closet..... The real question is: where's the current really going during a lightning storm??? Probably through the smallest, lowest voltage supperssor in the system!!!!! Neat stuff ==== there's an IEEE SPD (Surge Protective Devices) meeting series next week in Clearwater Florida if anyone's interested --- I'll be there....... Lot's of discussion about lightning and it's effects in both ac mains and the telecom world..... Best Regards, Michael Hopkins Manager, Customer Technical Center Process Instruments Division Thermo Electron One Lowell Research Center Lowell, MA 01852 Tel: +1 978 275 0800 ext. 334 Fax: +1 978 275 0850 [email protected] From: [email protected] [mailto:[email protected]]On Behalf Of Joe Randolph Sent: Thursday, April 27, 2006 5:22 PM To: Grasso, Charles; [email protected] Subject: Re: Surge testing limits - research question On 4/27/2006, Grasso, Charles wrote: Does anyone know of ( and hopefully access to) research that documents typical surge levels found on an AC mains distribution in a home as a result of lightning activity.?? I agree that C62.41 is a good place to get some basic information. In my experience, a surge withstand of 10 KV on the AC mains is needed to provide good reliability in the field. Similarly, a surge withstand on a phone line interface of about 5 KV is needed. However, that is not the whole story. Things get interesting if the product has multiple ports or there are multiple pieces of equipment connected by a LAN or USB. I have seen some unusual failure modes where a surge entered on the AC mains port and exited through the phone line, or where it entered on the phone line of a PC modem and then traveled on a USB cable to exit through another piece of equipment. Ironically, sometimes these alte! rnative paths are facilitated by certain "protection" devices that had been installed on one or more ports. Lightning always seeks the lowest impedance path to earth, and sometimes the path it finds is not one that the designers anticipated. This is especially true if certain portions of the installation are intended to be grounded through a 3-wire AC mains plug that in some home installations may not actually be grounded. Joe Randolph Telecom Design Consultant Randolph Telecom, Inc. 781-721-2848 (USA) [email protected] http://www.randolph-telecom.com <http://www.randolph-telecom.com/> - ---------------------------------------------------------------- This message is from the IEEE Product Safety Engineering Society emc-pstc discussion list. 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