John, Pat
Whereas you and I are used to systems that use 230 V, most readers of this forum are used to using 115 V systems and as a result the regulations are probably different. Also, if the trench was made of steel, would air cooling be needed - steel is probably much better. Having said that, I agree that 0.5 mm is a very tight tolerance. Regards Martin _____ From: [email protected] [mailto:[email protected]] On Behalf Of John Frewen-Lord Sent: 06 August 2009 08:50 To: U.S. Metric Association Subject: [USMA:45532] Re: I blew it! (The conversion of 2/100ths of an inch, that is) Hi Pat: I believe (any electrical experts here that could confirm this?) that cables are all based on a rational progression of their (metric) cross sectional areas. Even the cable to my electric kettle is shown in terms of its mm2 value. I would imagine that the 2 inch value is a (rough) approximation of its actual metric diameter, for the benefit of the US public. All this still doesn't answer the nagging questions in my mind how this state of affairs came about. It looks like a lot of finger pointing over some error discovered somewhere when things didn't fit, likely on the drawings or specifications and long before construction actually took place. The 0.5 mm 'error' turned out to be a convenient hook to try to hang an accusation on. Cheers John F-L ----- Original Message ----- From: Pat Naughtin <mailto:[email protected]> To: U.S. Metric Association <mailto:[email protected]> Sent: Thursday, August 06, 2009 8:04 AM Subject: [USMA:45531] Re: I blew it! (The conversion of 2/100ths of an inch, that is) Dear John, I noticed the closeness of 2.52 inches and 64 mm and then I wondered whether they were trying to fit a metric cable into an old- pre-metric space or vice-versa. On another issue from the same article, I wondered about where in Italy you could buy a 2 inch cable. This would be a most unusual size in Italy and would have to be a special order as I don't think any Italian cable maker would routinely make products to inch sizes. Cheers, Pat Naughtin Author of the forthcoming book, Metrication Leaders Guide. PO Box 305 Belmont 3216, Geelong, Australia Phone: 61 3 5241 2008 Metric system consultant, writer, and speaker, Pat Naughtin, has helped thousands of people and hundreds of companies upgrade to the modern metric system smoothly, quickly, and so economically that they now save thousands each year when buying, processing, or selling for their businesses. Pat provides services and resources for many different trades, crafts, and professions for commercial, industrial and government metrication leaders in Asia, Europe, and in the USA. Pat's clients include the Australian Government, Google, NASA, NIST, and the metric associations of Canada, the UK, and the USA. See http://www.metricationmatters.com <http://www.metricationmatters.com/> for more metrication information, contact Pat at [email protected] or to get the free 'Metrication matters' newsletter go to: http://www.metricationmatters.com/newsletter to subscribe. On 2009/08/06, at 4:32 PM, John Frewen-Lord wrote: As a surveyor in the construction industry (and having worked in both imperial and metric in the UK, the US, Canada and South Africa), something about this story doesn't quite ring true. 1. In-the-field tolerances are never less than 1/16" imperial (1.6 mm), or 1 mm metric (at least I've never come across tolerances tighter than that, and that includes a lot of precision hospital work). The 2/100ths of an inch is almost exactly 0.5 mm, a tolerance virtually impossible to achieve on a construction site. 2. The 2.52" is almost exactly 64 mm. Allowing for a tolerance of say +/- 1 mm, the trench should have been specified at 65 mm. 3. I'm no electrical expert, but I do know that cables when conducting electricity heat up and expand. Was no allowance made for this? And would it not have been wise to allow a tiny bit of airpace between the cable and trench walls to allow air circulation and help the cable to stay cool(er)? I wonder if there's more to this story than is being told? Cheers John F-L ----- Original Message ----- From: [email protected] To: U.S. <mailto:[email protected]> Metric Association Sent: Thursday, August 06, 2009 12:07 AM Subject: [USMA:45529] I blew it! (The conversion of 2/100ths of an inch, that is) OK, I got my conversion wrong. But I bet we would be using whole numbers in millimiters if we were using and familiar with metric and had adopted millimeters for construction as Pat has observed works best in industry. -- Ezra
